Pablo Artal Blog

Correcting presbyopia with corneal inlays: ¿reinventing the wheel or the advantages of simplicity?

2012-01-31T11:48:00.000+01:00

Prof. Artal. I did not realize how important was my near vision until a few years ago I became a presbyope. From then, I used reading spectacles, but I also searched the internet for new solutions. I was interested in one of them called inlays. Honestly, I did not understand well their operation mode. I would appreciate some information. “A curious presbyope”, Vancouver, Canada.

Again, a long time passed since my last post… Yes, this is the first entry in 2012. Any excuses? of course, a lot of travel during the last weeks (as a reward, see some pictures below!), and even more than usual commitments requiring most of my time. So, it is not surprising that this post arrives when January is nearly over. The good news is that I have renovated energies to cover a topic that I know is of great interest for everybody, especially for those over 40 years old. I received some questions similar to this one, and although my frequent readers know that this is not a medical blog and I cannot answer any personal issues (see my disclaimer!), this particular one on corneal inlays was general enough to be of interest for a large audience. And in addition, we have been doing a lot of work on this new device recently, so this is a perfect timing!

Presbyopia is... an ocular condition characterized by the inability to focus near objects. With age, the crystalline lens losses its capacity of accommodation by changing its shape to focus objects at different distances. Presbyopia is a very “democratic” phenomenon. Nobody reported a case where accommodation was still present at certain age. The symptoms however are very variable and the impact would depend on the refractive state of each person. For instance, hyperopes would suffer earlier from presbyopic symptoms.

Of course, a search for a cure, or at least a partial solution, for presbyopia has been the Holy Grail in Ophthalmology. Optical solutions to improve near vision in presbyopic subjects can be classified as surgical or non-surgical methods. The non-surgical solutions include the use of spectacles (bifocals or progressive power lenses) and multifocal contact lenses with profiles designed to improve the depth of focus of the eye. Although widely used, progressive power spectacles typically require a custom adaptation period due to the distortions around the progression zone. We did extensive work on progressive power lenses during Eloy Villegas’ PhD thesis a few years ago (this can be a future post). Multifocal designs in contact lenses are usually limited by physical constraints that regulate the optical quality of near and intermediate focus at the expense of less quality in the primary (far) focus. Among the surgical techniques, there are a variety of intraocular lenses (IOLs) designed to improve near vision for presbyopes such as multifocal IOLs (diffractive or refractive designs) or the so-called accommodative IOLs. This is a solution only adequate when you already have cataracts, so in many cases you would have years of suffering presbyopia. All the current solutions have pros and cons. For example, diffractive lenses might suffer from glare and scatter light. On the other hand, the clinical trials with those so called accommodative IOLs present non clear results so far and possibly they do not actually accommodate. There are also some surgical interventions reshaping the corneal surface to increase depth of focus as possible solutions: presbyLASIK or intracorneal femtosecond laser. These are today non complete solutions and non-reversible and permanent.

Corneal inlays... There is another, conceptually very simple, alternative to increase depth of focus in the eye as a correction for presbyopia: intra-corneal small aperture implants, as mentioned by my correspondent. One of the devices is called KAMRA, manufactured by AcuFocus, a company in Irvine, California, USA (http://kamrainlay.com/). The operating optical principle of this device is notably simple: just a small aperture mask with a diameter of about 1.6-mm implanted into the corneal stroma provides a significant increase of the depth of focus of the eye. That is to say, objects would appear in focus at most distances. I am sure you played with this principle just by looking through a small hole you produced with your fingers… and things looked sharper.

This figure illustrates schematically the situation. A presbyopic eye focus the light coming from a point source at infinite onto the retina through a 4-mm pupil diameter (blue) and through a 1.5-mm pupil diameter (green). With the small aperture, the retinal image does not spread out so much as in the 4 mm case does when is defocused. This simple approach provides no multifocality but a theoretically large tolerance to defocus that might be sufficient for performing typical near visual tasks. A possible disadvantage of the method comes from the obvious reduction in the amount of light reaching the retina.

To reduce this effect the small aperture inlay is implemented in an annulus (see picture) and implanted only monocularly. The inlay is a polyvinylidene fluoride ring that contains particles of carbon to make it opaque. It is 0.01mm thick and has a central aperture of 1.6 mm and an outer diameter of 3.8 mm. The surface of the inlay is perforated with 25 mm holes arranged in a random pattern to allow nutritional flow through the corneal tissue. It has a 1600 random-hole pattern with an average light transmission of 7.5%.

When a few years ago, in a very hot day in the middle of the Murcia summer, I received the visit of some members of the AcuFocus management team, interested in our visual optics expertise, I must recognized that my first reaction was to think in that idea as if somebody wanted to explain you the wheel mechanism! However, although I was very skeptical initially, I noticed a lot of enthusiasm in one of the visitors who actually had implanted the inlay. Then, I decided to help and performed both optical calculations and visual testing with our adaptive optics visual analyzer (http://pabloartal.blogspot.com.au/2009/08/binocular-adaptive-optics-simulator.html). This offer the opportunity to try myself the inlay, without the need of the surgery!

We explored how the mechanism of binocular summation works in a situation like this, when one eye forms the images through a normal pupil diameter (4 mm) and the other eye through a small pupil (1.5 mm). The visual results were published last year in an article in IOVS (http://lo.um.es/publicaciones.php?cat=1&id=381) and the optical simulations results appear in the February issue of the Journal of Cataract and Refractive Surgery (http://www.jcrsjournal.org/article/S0886-3350%2811%2901796-2/abstract).Juan Tabernero, Christina Schwarz and Josua Fernandez were my co-authors in these articles.

We demonstrated that this conceptually simple solution, the small aperture, have the capability to increase depth of focus with good visual acuity. The average binocular acuity of three subjects in the study was over the J3 level (0.5 decimal acuity) from 0 to 3 D range (this covers a distance from far to 33 cm). There are certain limitations to the small aperture approach. Some of them are clearly intrinsic to the technique, like possible diffraction effects due to the pinhole size or the decrease in the light intensity reaching the retina. However, the results of acuity at best focus conditions did not show a negative visual effect. The impact of the reduction of light intensity in the retina is attenuated with the monocular implantation. A non-intrinsic problem might be related to the aperture decentration. Typically, the center of the pinhole is placed as close as possible to the visual axis, using the corneal reflex as a reference. If the aperture is not properly centered, a more peripheral part of the cornea would be used to form the retinal image and the quality of vision may be reduced.

But, it works? Yes, our results showed that this simple solution to increase depth of focus actually works. Of course, as with any medical device, you should first evaluate all the pros and cons. It actually provides reasonable vision at all distances and can be removed if necessary. On the negative size, decentration of the inlay can degrade vision and some subjects may complain under dim light.

I have to recognize that something as simple as a hole, reengineered very cleverly is a nice step forward towards a practical way to correct presbyopia. In the near future, it would be a nice advantage if each prospective patient could first try the procedure with a dedicated adaptive optics-type visual analyzer instrument.

An interesting and complementary article on the optical properties of the inlay (Tabernero & Artal) has just appeared in this month issue of the Journal of Cataract and Refractive Surgery.
http://www.jcrsjournal.org/article/S0886-3350%2811%2901796-2/abstract

And to finalize this post, as usual, some news, comments and curiosities...

Too many bicycles? The first week of the year I was in Holland. I had the opportunity to take this picture. Dozens of bicycles in the water canals!

Bart Jaeken PhD defense. Bart completed successfully his PhD a couple of weeks ago. I realized that Bart was my PhD student number 18! This is a clear indication of how old I am! The picture below was taken at the Restaurante Morales (one of my Murcia favorites with well prepared food with the best ingredients) after the defense with the jury and happy Bart. From left to right: Juan Tabernero, Frank Schaeffel, Susana Marcos, Pedro Prieto, Pablo Artal, Juan Bueno, Maria Yzuel, Alejandro Mira, Bart Jaeken and Antonio Guirao.

Antipodes. Last week I was in the north island of New Zealand during a couple of days in my return to Sydney from Spain via California. This completed a round of the earth after departing Sydney via Bangkok in Decemeber. This was my first visit to the Spain’s antipodes and I really liked very much NZ, including the local spring water with a more than appropriate name!

Tabernero, J., Schwarz, C., Fernandez, E., & Artal, P. (2011). Binocular Visual Simulation of a Corneal Inlay to Increase Depth of Focus Investigative Ophthalmology & Visual Science, 52 (8), 5273-5277 DOI: 10.1167/iovs.10-6436

Optics research and the eye in Spain during the XX century: a brief history

2011-12-27T18:19:00.002+01:00

Dear Pablo. I recently movedto a new postdoctoral position in biomedical optics. This is a new field for mesince my PhD was in laser physics. A colleague passed some of your papers and I wasa little surprised to see that many of the most significant recent contributionsin the field of the eye’s optics come actually from your lab and other groupsin Spain. Are there any reasons to explain this notorious Spanish contributionin this area of science? Li, Taiwan.

This is again (as many of the questions of thisinfrequent blog!) a common question I receive from friends and colleagues. They often askwhat is special about Spain to be comparatively so productive and innovative inthe area of Visual Optics internationally. Unfortunately, Spain tradition andcontribution to science in general is not at the level of the importance of thecountry, its size and relevance in other aspects of human activity. This hasbeen an important problem and is even more relevant now with a deepeconomic recession. However, Spanish science is significant, especially in someareas where a tradition started before the Spanish civil war (in the 30’s ofthe past century) and developed from the early 50’s steadily untiltoday. Nowadays, and just by the number of publications, Spain is ranked aroundthe number 10 country in the world. However, in terms of relative impactbased in citations, we are well below. It could be said that as a country, we wereable to produce science in reasonable quantity but not yet in good quality. Therates of transference of results from the lab to industry are also in general very poor as compared with others.But the general point I would like to make here is that in those cases (and I willconcentrate in my own field here) where Spain’s presence is significant today, this is due to individuals from the last century that actually built a tradition for us. This is an important message for young people... remember those advacing the field before you!

Science is an activity that in many aspects issimilar to wine making. It requires good conditions, special and sustained careand tradition. In the case of the eye’s optics research, there isan interesting historical revisionarticle (in Spanish) that I actually used in part as a base for this entry(Marcos, Artal, Santamaría, Aguilar, Plaza. Opt. Pura Apl. 39 (3), 189-197, 2006).

The early days. A key initial figure in the Spanish Physiological Optics was José María Otero (see portrait extracted from an issue of theJournal of the Optical Society of America in the early 50’s). Otero was thefounder of the Instituto de Optica in Madrid, where most of the action originated.He was a remarkable person (I heard that a biography was recently prepared, but I didnot have a chance to see it yet). He (with Armando Durán) did significant contributions in Vision research,rediscovering the phenomenon of night myopia (in the dark, we tend to be relativelymore myopic). By the way, I will prepare next year a full entry dedicated tothis fascinating problem (I already received several questions from readersafter my presentation in ARVO revisiting this topic). Otero had a lot ofinfluence in the development of Spanish science during the Franco regime. Hewas not only concentrated in optics, but had interest in many other areas andwas also the founder of the Spanish nuclear agency. Otero, amilitary engineer trained in Berlin, started upon his return to Spain in 1934the Navy Optics Laboratory (where he worked on optical design). Hesimultaneously joined the Rockefeller Institute of Physics and Chemistry of the“Junta para Ampliación de Estudios” (primary research institution in Spain,first presided by the only Spanish science Nobel laureate (working in Spain), Santiago Ramón y Cajal), and five years later chaired the Optical Section(Institute of Optics afterwards) of the “Consejo Superior de InvestigacionesCientíficas”. He recruited a group of young researchers well trained ingeometrical optics, optical materials or colorimetry. In the early 40’s thegroup worked in a project to design optical components for periscopes insubmarines and binoculars. They conducted measurements of visual performance underlow illumination and found a systematic myopic shift in night conditions (thementioned night myopia).

In the early 50’s, the Instituto de Optica moved to anew building and was already a rather unique scientific organization comparedwith the obscure circumstances of the time in Spain. As an example, in 1953, theInstitute hosted a colloquium on the problems of Vision as a part of theInternational Commission for Optics conference (ICO3). Yves Le Grand, W.S. Stiles, R. Granit and C. Wald (these two laterNobel laureates) gave invited lectures on binocular vision, thresholdsensitivity, chromatic vision and the chemical basis of vision. Among othersparticipants of the meeting there were some of the best known names in thefield: A. Arnulf, F. Campbell, R.A. Weale, W. Wright. G. Toraldo, M. Ivanoff, B. O’Brian.

Double-pass system: from Paris to Madrid. After some less excitingyears (Otero probably was more dedicated to other activities), in the early70’s, Lorenzo Plaza, at the time director of the institute ofOptics hired A. Arnulf after his retirement in France. Arnulf wasone of the most influential optical scientists with interest in the eye of themid XX century. It was a nice coincidence that at the same time, two young graduates moved fromthe University of Zaragoza (Javier Santamaría and Julián Bescós). Theywere nearly to finish their PhD thesis under the supervision of another influential personin recent Spanish optics (María Yzuel (Marifi), later a professor at the Autonomus University of Barcelona). They were welltrained in optical image processing and they learn about the eye with Arnulf. Thatwas an outstanding combination! They built a series of new experimental devices tostudy the microfluctuations of the accommodation based in imaging thecrystalline lens by using the Foucault technique in two dimensions with annularapertures. Although they were able to obtain nice pictures of the lens shadows,the technique was too complicated and the data difficult to evaluate. Then Arnulfsuggested analyzing the microfluctuations of the accommodation by the directrecording the double-pass retinal image of a point source after reflection inthe retina. He already had used that technique in France with a line source.The team decided to use a laser point and an image intensifier device and thenobtained for the first time dynamic recording of the double-pass retinal imagesin the living eye. These series of experiments were the precursors of many oftoday’s activities in experimental visual optics in the country and around theworld. See the pictures below of the prototype of binocular double-passinstrument (called VIRIOM at the time) and examples of retinal images (picture courtesy of Javier Santamaría). This wasclearly too advanced for that time. Even today, only monocular systems based in this concept are usedin the clinical practice.

The more recent times. I was fortunate to “land”in the Institute of Optics in Madrid in the mid 80’s. After my Universitytraining as an optical physicist at the University of Zaragoza. Optics at Zaragoza was also somehow related to the Institute of Optics inMadrid. Justiniano Casas formed that school aftermoving from there. So, in a way my trip to Madrid was not unusual, simply then inthe opposite direction. By the way, how different was traveling at those days,no so remote… I clearly remember traveling from Madrid to Zaragoza (330 km) ina night train probably taking 6 or 7 hours. Now, the AVE (Spanish high speedtrain) took this distance in a mere 75 minutes! My PhD thesis still was a clear continuationof Arnulf’s endeavors and supervised by Javier Santamaría. I was asked to record the retinal image of apoint source using a linear camera (then the available cameras were still basedin tube technology). I think we did a good job to show the potential of thedouble pass technique to characterize the eye’s optical properties. More than25 years later, these ideas have been transformed into a clinical instrumentthat is successfully used to detect cataract in an objective way. This canprovide prospective patients with a clear diagnosis that can avoid years ofpoor vision. The same instrument can be used to assess the opticalquality of the tear film. This could contribute very substantially to theevaluation of the use of different therapies with patients suffering from thisdebilitating condition. (More information in a recent post: http://pabloartal.blogspot.com/2011/11/evaluating-dry-eyes-new-optical-method.html

I am personally proud to continue the tradition of those remarkable scientists bringing together the state or the art optical technology to better understand and improve human vision.

Spanish visual optics in a paper tablecloth. A couple of years ago,during a lunch break at the European meeting on Physiological Optics in Stockholm,two colleagues and good friends, Klaus Biedermann and Vasyl Molebny asked me a similar question as Li did. I preferred toexplain them the whole process with the help of a schematic diagram in our paper tablecloth. See pictures (courtesy of Klaus Biedermann), in one I am writing the scheme with Vasyl at my left side. I am happy to tell you that today, the tradition is in a pretty good shape. A group ofyoung scientists are well trained and able to continue and move further. And the current director ofthe Instituto de Optica in Madrid is Susana Marcos. She actually was my first PhDstudent and now has a successful own group working in this field.

What’s next? I would like to see how ourefforts in basic research are moving to more real applications,ideally with our own research-based companies. I think that spin-off companies as Visiometrics and Voptica are in the good direction, but they are not enough. My personal dream is double: to maintain our role as a key worldplayers in basic research and to built a solid and succesul own optical industry. If we couldcreate teh basis for a tradition of an optical industry would be great! (I am thinking insomething such as Zeiss-type tradition of the German optics industry!).

Pictures from 2011. And as a festive end ofthis post, I selected some pictures I took in different locations around the worldduring this year 2011: Salzburg, Vancouver, San Francisco, Seville…

And my best wishes for 2012. This is the lastentry for 2011. I would like to take the opportunity to wish all my readers ofthis blog the best for 2012. This is our lab greetings card for you! A picturetaken last week with the city of Murcia behind us.

Marcos, Artal, Santamaría, Aguilar, Plaza. (2006). Research in Physiological Optics in Spain: A historical revision Opt. Pura Apl. 39 (3) 189-197

Evaluating dry eyes: a new optical method to determine tear film quality

2011-11-08T02:07:00.004+01:00

Dear Prof. Artal. Iwas diagnosed with a dry eye condition a few years ago. I routinely visit myeye doctor to be treated and evaluated. Being a scientist myself, I found alittle bit frustrating that most evaluations come from my subjective responsesto questionnaires. And it is difficult for me, and I suppose forother people, to really say if I feel my eye a little bit better or worse thatin the previous visit. It seems surprising that for a so common disease thereare not yet well established and simple objective evaluation methods. Do youknow of anything new available to follow up and evaluate dry eyes? Joanne, Los Angeles, USA.

This question from Joanne (again received already atleast a couple of years ago, sorry for the long delay) is actually very good.Some relatives also used to ask me about doing “something” to help people withdry eyes. I am quite fortunate to have a pretty good tear film. But I canimagine what difficult and miserable life can have millions of people sufferingsevere tear film problems, what is commonly referred as dry eye. I became moreand more interested about this problem and in particular I tried to apply someoptical (non-invasive) techniques to evaluate how good, or bad, is the tearfilm. And I am happy to tell Joanne and other readers that we started doingsomething in this direction and after several years of work we recentlypublished an article in the Journal of Cataract and Refractive Surgerydescribing a new optical method we developed to measure tear film quality.Antonio Benito and Guillermo Pérez from my lab, Sandra Mirabet and José MariaMarín from the Arrixaca Murcia hospital and Meritxell Vilaseca and Jaume Pujolfrom UPC in Barcelona were my the coauthors in this paper. (Benito, A., Pérez, G., Mirabet, S., Vilaseca, M., Pujol, J., Marín, J., & Artal, P. (2011). Objective optical assessment of tear-film quality dynamics in normal and mildly symptomatic dry eyes Journal of Cataract & Refractive Surgery, 37 (8), 1481-1487;http://www.jcrsjournal.org/article/S0886-3350%2811%2900732-2/abstract; http://lo.um.es/publicaciones.php?cat=1&id=304).

However, my interest in the tear film isactually pretty old. When I was a graduate student working for my PhD inMadrid, I spent a few months at Cambridge University in the UK. During thattime (probably around 1987) I was around the Physiological Laboratory with thelate professor Fergus Campbell. At the same time, Jeremy Prydal was building an interferometer to measure the thickness of the tear film. I helpep in his endeavor and some years later there was a paper published in the IOVS journal. (http://www.iovs.org/content/33/6/2006.abstract?sid=b2d361e0-5a41-4e67-a54d-e5999ca2f1e0).

The short time I spent in Cambridge was quiteimportant for me and my future scientific career. It surely opened my mind. Iremember myself in the early years of my PhD as a very biased physics post-graduate studentwith a clear aversion to any implication of my work being “too” biological! Although I startedmy PhD work on the eye’ optics, I used to convince myself that my approach was that ofan optical engineer. In Cambridge, I believe I began to understand that the eye’soptics was actually important as the first stage for vision. As a physicist, Iwas perhaps too much oriented to the instruments, butthat was changing, I guess for the good. In Cambridge, I was also fortunate to meetmany influential figures in vision research that were there at the time. And evenmore fortunate to become long-time friend of some other great scientists that had been there before as DanGreen or Denis Pelli. At that time my interest in the tearfilm was to know some geometricaland physical parameters by using optical techniques. I alsorealized the intimate relationship between the quality of the tear film and thequality of vision. I still clearly remember an unpublished experiment with Jeremy Prydal as subject, where vision was tested with some drugs distorting the tear were instilled in his eye. I always returned from time to time to the tear film… that beautifullyengineered first surface of the eye’s optics (when is working). By the way, I foundsome old pictures from Cambridge. Not sure if you could recognizeme in this one…

PabloArtal cycling in Cambridge (UK) circa 1987

After many years, I was again interested more inoptical approaches to evaluate the quality of the tear film. I was convincedthat a better diagnosis and follow-ups approaches were necessary in order toimprove treatments and the quality of life in those dry eye suffering patients.

Tear film quality is related to retinal imagequality…The optical qualityof the retinal image is the result of the pass of the light through the ocularstructures. The tear film is the first medium that modifies the optical path ofthe light reaching the retina. The impact of the tear film on the quality ofthe retinal image highly depends on the homogeneity of the tear pellicle. Theloss of homogeneity in the tear film modifies its thickness locally and due tothe refractive index variation across the interface air-tear, this may imposesignificant differences on the eye’s aberrations. Moreover, local small changesin the tear film increase the light scattered in the anterior surface of thecornea, affecting the overall ocular scatter. The changes of both ocularaberrations and scatter degrade the retinal image quality. The issue of scatter has been already discussed in previousposts that perhaps you are now interested in re-read:

http://pabloartal.blogspot.com/2011/05/glare-or-blur-scatter-or-aberrations.html

http://pabloartal.blogspot.com/2009/03/scatter-and-spherical-aberration-good.html

Since the quality of the tear film may have a largeimpact on the retinal image, an indirect approach could be used, based in theanalysis of the retinal image as an indicator of tear filmquality. And in fact, the objective technique we developed is based on double-pass retinal images. This has also a long time history forme, since we recorded the first retinal images of a point source were recorded using a double-pass instrument during my PhD thesis in Madrid. Sincethen, many different studies and applications of the technique (called thedouble-pass technique) have been carried out. Something specially interesting was that these ideas evolvedfrom the research laboratory to the real clinical world. A spin-off company,started in Tarrasa (near Barcelona), called Visiometrics (www.visiometrics.com), developed anddistributed all over the world a clinical double-pass instrument, called OQAS. Fromtheir beginnings, in the late 90’s, I helped the enthusiastic and good friend JaumePujol, an optics professor at the Polytechnic University of Catalonia,to convert lab prototypes into real user-friendly instruments. In this adventure, otherremarkable individuals have been also involved. Jose Luis Guell, one of the leading Europeanrefractive surgeons and Jan Bonel in the business side. (Ipromise a future post with some historical comments and details on thedouble-pass instrument and its influence in visual optics in Spain).

Schematicpicture of the double-pass principle to record retinal images

We actually used one of this double-pass OQAS instrumentsto perform the tear film analysis. In particular, we used a dynamic analysis ofdouble-pass retinal images as an indirect indicator of the relative quality ofthe tear film in two groups of normal and dry-eye subjects. In normal eyes,after blink, the retinal image remains stable for a relatively long time, wellover 20 or 30 seconds.

However, in dry eye patients, after blink, the tear deterioratequickly and then, the retinal image also is disturbed. As you can see in thispicture below, after the blink retinal images (pictured here every half seccond) is first stable (similar size and pseudo-color) and then becomes larger indicating a blurred vision caused by a deterioration of the tear film.By calculating an index from each retinal image, it is possible to determine an objective tear film break-up time. See the figure bellow as a niceexample. In most normal eyes (open symbols below the black line), after blinks the parameter remains stable (asdoes the retinal image), but in the dry eye patient (solid symbols), after about 5 seconds, very quicklyincreases.

I believe this new objective optical method to theindirect evaluation of the quality of the tear film can be of potential help. Itis sensitive to detect symptoms of dry eye and to differentiate from normalcases. The procedure may allow early detection and follow-up of tear-filmrelated patient’s complaints. My hope is that this noninvasive approach, combinedwith others, would promote a better detection, and in particular a bettertreatment of dry eye conditions. I am sure that many silent patients, as mykind correspondent Joanne, would really appreciate our efforts.

Of course, dry eyeis a very complex condition. I think this is a step in the good direction ofhaving better diagnosis methods. However, as always in science and medicine,multiple approaches are always safer. Our study adds a new and complementaryapproach that in the near future, when a norm database would be established, will bemore and more useful. At least this is my hope!

On scientists and politicians… perhaps are not so different. I have recentlypublished an opinion article on this issue (also partially discussed in a previouspost: http://pabloartal.blogspot.com/2009/11/science-and-politics-and-scientists.html).You can have a look at the article (in Spanish) at the El Pais newspaper web site: http://www.elpais.com/articulo/sociedad/Cientificos/politicos/buenos/malos/elpepusoc/20111102elpepusoc_19/Tes

Barbecue time in Australia… for somebody like, me adapted tothe northern hemisphere clock, being in November and progressing to the summerweather… it is rather bizarre. Although, of course, absolutely normal for Australians.They are nicely obsessed with open air barbecues. Last Sunday, I was in my first Australianbarbecue. The location: a peaceful and nice park in Mosman, a suburb north Sydney(see photo). What that photo does not tell you is that if you walk a few metersfrom the barbecue site, you can enjoy this magnificent view of the city…

Benito, A., Pérez, G., Mirabet, S., Vilaseca, M., Pujol, J., Marín, J., & Artal, P. (2011). Objective optical assessment of tear-film quality dynamics in normal and mildly symptomatic dry eyes Journal of Cataract & Refractive Surgery, 37 (8), 1481-1487 DOI: 10.1016/j.jcrs.2011.03.036

Optics and vision: how the eye affects your quality of vision?

2011-10-11T07:53:00.010+02:00

Hello Pablo. Perhaps one of the most interesting topics today in the area of physiological optics is the relationship between the ocular optics and vision. I know this has been a subject of study for decades, if not centuries, but I would appreciate if you could elaborate more on your current views of this exciting problem. Martha, Sydney, Australia.

How the eye limits the quality of vision is indeed a central and basic problem, but also with lots of potential applications in clinical optometry and ophthalmology. Curiously, for many people this sounds so simple that perhaps they are surprised why we should be even talking about this. As simple as this: if you have good optics you would have good vision and if you have bad eyes you will have bad vision. Why to worry? Well because, it is wrong… and as always life is not as simple.

In one way or another, my own research has been for many years directed to better understand the relationship between the eye and vision. In some earlier posts, I have already covered partially this problem. For instance, in how chromatic and spherical aberrations affects vision (http://pabloartal.blogspot.com/2010/02/chromatic-aberration-of-eye-to-correct.html). But, I agree with Martha that can be a good moment to summarize here what we know about this.

The visual system as a beautiful economical design… The visual system is an exceptional combination of different physiological elements that constitute our main window onto the world. The objective of the visual system is to analyze appropriately the images received from the outside world. The first step is the formation of these images on the retina. As an optical system, the task of the eye is to project onto the retina images of an acceptable optical quality under various conditions, which will then be processed. For me in particular, as a physicist, this is the most important stage in the visual system. If the eye, as an optical instrument forming the retinal image, does not work correctly, the entire visual system will not be operational. The images projected onto the retina are digitalized in the photoreceptors and other retinal cells at different levels: spatial (in terms of the position), chromatic (according to the spectral composition of light) and temporal. These signals are then sent to be processed and interpreted in the visual cortex. The beauty is that the capacities of each phase in the visual system appear to be well adjusted between themselves. This is an example of economy in the design of the system, which has no doubt been optimized over the course of evolution.

Eye’s optics… The human eye is a very simple optical system compared to most artificial optical instruments, but it places fundamental limits on our visual capacity. It is made up solely of two converging lenses (the cornea and the crystalline), a diaphragm (the iris) and a screen (the retina). Even when the image is formed at the right focal point, the eye, just like every other optical system, is not perfect. that is to say that the image of a particular object will not correspond to another perfect point on the retina. An eye with high optical quality will form a very small and compact image, whilst in the opposite case the point will be blurred and spread. A system that is highly affected by aberrations has poor optical quality and produces spread retinal images. It has been well known, since the time of Helmholtz in the mid-19th century, that the eye is not a perfect optical system, even when it does not suffer from any so-called refractive error (defocus and astigmatism). The type and quantity of aberrations depend on the person and on a variety of factors, such as the size of the pupil, the entry angle or the accommodation state. On average, in young people with normal eyes, aberrations for a 5mm diameter pupil are of a magnitude of 0.25 μm RMS. This is equivalent to a defocus of approximately 0.25 dioptres, what most clinical readers will consider to be low, near to the typical measurements errors.

Optics and vision… If, in a group of observers, one measures the optical properties of each eye and one makes various visual assessments, it is possible to define the way in which optics influence visual quality. The experiment is simple and, in one way or another, has been used as a basis for numerous studies. The simplest way to evaluate the effect of optics in vision is by adding defocus. When defocus reduces the quality of the image on the retina, visual acuity is reduced too. Optics and vision are indeed clearly related. However, this correlation is not as good for small defocus values, when their magnitude is similar to the other aberrations present in the eye. Various researchers have attempted to define the most appropriate optical quality parameters to predict visual quality. There exists a general agreement that the parameters calculated based on measurements on the retinal plane (such as the PSF) are more efficient that those estimated based on measurements on the pupil plane (such as the aberrations RMS). The following step consisted in understanding the exact effect of aberrations on visual quality. This phenomenon is more subtle than the impact of defocus because the relative impact of aberrations is generally much smaller. In terms of quantity, it would appear clear that if an eye is affected by more aberrations, the visual quality of the person concerned will be less. And this is indeed the case when the aberrations are above normal (more than 0.3 μm RMS for a 5mm pupil).

Different scenarios… In eyes with normal aberration values, the impact of the latter on visual acuity has to be explained according to a variety of scenarios. A purely “physical” option would suppose that eyes with less aberrations and even eyes that are perfect from an optical point of view, offer better vision. Another alternative could suggest that the best option for good vision would be an eye with specific optics affected by a given type of aberration (for example a vertical coma). The final option developed by recent studies on neuronal adaptation (already discussed here in a previous post: http://pabloartal.blogspot.com/2008/11/neural-adaptation-to-eye-optics.html) would have it that optimal optics are optics specific to each individual (to which each of us adapts over time).

The experiment... To make the distinction between these various options and to find out more about the puzzle of the relation between optics and vision, we performed the following experiment. We identified a certain number of subjects with good or very good visual quality. In practice, this was a group of young students with decimal visual acuities of between 1 (20/20) and 2 (2010). The optical quality of each of them was measured precisely. Quite surprisingly, no link was found between optical quality and visual acuity in this group of subjects. It may be concluded, therefore, that people with high visual acuity are not specifically those whose eyes benefit from the best optical quality. This demonstrates that it is not necessary to have exceptional optical quality to benefit from exceptional visual quality. It should be noted, however, that this does not mean that it is impossible to improve the visual acuity of a given individual by correcting aberrations in the laboratory. The reason why optical aberrations and visual acuity are not correlated is due to the fact that other factors exist, which we have not yet taken into account. It is right to say that the optics of the eye are not only affected by aberrations but also by intraocular scatter (see previous related post: http://pabloartal.blogspot.com/2009/03/scatter-and-spherical-aberration-good.html). In young, normal eyes, its effect may only be small, even though it is acknowledged that it increases gradually with age and may completely dominate the deterioration of images in case of cataracts (see previous post: http://pabloartal.blogspot.com/2011/02/how-can-i-know-if-i-have-cataracts-and.html).

In summary... Over these years we have made considerable progress in the knowledge of the relationship between optical and visual quality. Today, the impact of retinal image quality on vision is understood much better. In addition to the pure advances made in knowledge that this represents, this progress will have a beneficial effect in the near future on the development of new strategies and solutions for more sophisticated and, above all, more efficient visual correction.

X anniversary of the Academy of Science of Murcia… Last month during my visit to Murcia, we had a special formal evening event. We celebrated the X anniversary of the Murcia Academy of Science. I have the honor to be, since last year, the president of the Academy. During that event, Prof. Rafael Rebolo was named honorary member of the Academy. Prof. Rebolo is a worldwide recognized astrophysicist working in the Canary island and with strong ties to the city of Cartagena.

Prof. Rafael Rebolo and Pablo Artal

X anniversary of the Murcia Academy of Sciences. From left to right: Angel Campos, Alberto Aguirre de Carcer, Pablo Artal, Jose Antonio Cobacho, Felix Faura, Tomás Barberán, José Ballesta & Carlos García Izquierdo.

Omi, the dog... I received some emails asking about Omi, my dog. On his behalf, thanks for asking… is doing well (see recent picture although missing my walks)

Hey mate! Believe it or not after weeks in Australia, hearing all the time this expression that people use very often to greet each other... I was not able to recognized the spelling! Finally, I got it and I was relieved... I know now what Australians are telling me everyday.

Coogee beach pacific views… Now I am often walking (without Omi) along the coast in Coogee beach (eastern Sydney suburbs). Always some opportunities for nice pictures of the ocean.

Villegas, E., Alcon, E., & Artal, P. (2008). Optical Quality of the Eye in Subjects with Normal and Excellent Visual Acuity Investigative Ophthalmology & Visual Science, 49 (10), 4688-4696 DOI: 10.1167/iovs.08-2316

Advice to become a refined self-plagiarist. (Disclaimer: it is not ethical and will not help your career)

2011-08-31T07:00:00.012+02:00

Dear professor. I am a PhD student. As you may remember, being a student is tough. I did some original research during the last 3 years. I think is good stuff. Now is time to publish papers, secure my dissertation and start the solid foundations of my future career. I would like to have as many published papers as possible. I do not care if I repeat or manipulate something. I am not worry about what some old guys feel is or is not ethical. It is easy to talk about ethics when your salary is good and secure forever. This is my research and if I can have 7 papers, that would be better than having only 5. You are a journal editor so you should know how this world is. You do not know me, but I noticed that you spend some of your time answering people's questions. So, perhaps you want also help me with some tricks on what I should do to maximize the number of my published papers. Any advice would be welcome. I am prepared to do a lot of extra work on data and camouflage writing. I can try many different journals simultaneously. Any suggestion to avoid problems would be welcome. I would prefer a private answer, but if you cover my name and affiliation, it would be OK to have a public response too. X, XX, XXX.

This is a very bizarre question I received some time ago. My first reaction was: it is a joke!; my second reaction that this person was stupid talking so openly on doing actions that were clearly unethical and finally… I basically forget about that completely. However in the last months, I was involved in several real cases in different journals where some young (and sometimes not so young) authors were on purpose trying to act in the way described in the question. So, I decided to dedicate a post on this issue: “the refined self-plagiarist”.

I already dedicated an entry sometime ago about the problem of plagiarism: http://pabloartal.blogspot.com/2009/06/plagiarism-what-can-be-done-simply.html. You can have a look if you missed then. Plagiarism is a serious problem in scientific publishing. The good thing is that mostly everybody recognizes this as clearly an unethical practice (it is bad to use other’s material without proper recognition), that, if discovered, should be punished. However, the situation with the practices of self-plagiarism is not so clear. Many people do not even would think that is a bad behavior. They could argue that after all, “I can do what I want with my results”. Self-excuses can be numerous, for example the need of disseminating the results to different communities for the benefit of the different readers. When we approach the tenuous distinction of what is appropriate in terms of your own work, these questions are not easy to answer… what is good? what is bad? What can be done without much worry? And then, there is the possible expert and refined “self-plagiarist”… he does not care about ethics, only following the idea of maximizing previous efforts.

The history is old and repeated often. A piece of research that could, eventually being performed professionally, providing correct scientific results is multiplied in the form of many published papers. The final result: instead of one publication, the author can have several. In some cases, the very sophisticated self-plagiarist can produce many papers. The multiplicative factor is quite significant. Some people talk about this situation as “salami” publications. I would probably prefer to call this as “chorizo-slices type papers”… if you only count numbers, you think this is good for you, but…the bigger picture is that self-plagiarism impedes scientific progress by flooding the system with weak and redundant information. It can also hurt your career. Sure, it seems to benefit you if you merely count the number of papers you’ve published. But whenever someone assesses your body of work more closely, they will notice the redundancy. The proof of your fault will be there forever! Some other points for the self-plagiarist to remember:

Be careful… automatic publication duplication detectors. Although every scientific journal faces this problem in one way or another, not many openly address it. So, I liked an editorial of the journal ”Anaesthesia”, where the editor recognized that they detected an increased number of duplicate submissions (see link below). He was not sure if that was by chance or simply because the journal (as others) started using a specific software to look for repeated parts in publications. It is called “CrossCheck” (I do not have myself a direct personal experience on how it works). Then with this type of software being routinely used, life will be a little bit more complicated for the folks such as my correspondant… but still, there is some hope. A refined self-plagiarist is not so naïve to simply copy-paste same parts of an existing paper in other multiple ones. Such a clever person will do something more sophisticated, of course. For example, you have your data, whatever they are, and then you produce sets of different figures. You know that exact replica of figures in different manuscripts will help editors to recognize duplications. Then, you know that is possible to write a different introduction, although telling the same ideas basically, also you can have one paper with more details of the methods, other with more mathematical descriptions, and of course, you will be careful with the titles and the names of sections. You can do this very differently if you are clever enough… Here you have just one example:

Title paper 1: Facial tissues: a study on relative comfort

Title paper 2: Subjects responses on soft paper in contact to face skin

If you know the area, you can write a lot of different titles, with no use of the same words… so automatic software detectors would not be a problem for refined self-plagiarism.

How many you want?

But, always we will have clever and dedicated reviewers! Yes, you are initially (at least) right. You can do a lot of work to reorganize you research in several pieces that will not be detected by machines and even by human non experts… but, it is likely that one reviewer will notice. And the chances are reasonably high. The same reviewer perhaps received your manuscripts from different journals nearly simultaneously. Even if you are so refined to play with submission times, it would be also possible that the reviewer still remember. I have to say that this happened to me as a reviewer several times… and it is a joy for reviewers to say to the editor… here you have a clear duplicated publication. We all love that... And most editors will be always following the reviewer's advice in these cases… so you can be safe from machines, but you will never be safe from your colleagues in the field. And the good and bad thing about peer reviewer publication is that even if you manage to have the multiple papers... somebody, and sometime in the future will discover this. The proof of your fault will be there forever!

Supervisors… You were not mentioning in your letter a very important issue. You pretend you did your work alone, but I assume you have a supervisor. Then, your supervisor’s role is to be sure the papers you submit are all really independent and without overlapping. I should say that every paper should contain a significant amount of new science to be publishable. He will have the last word. You should not go ahead without his approval. Well, what may happen is the following. A too-nervous student or post-doc decides to submit a paper containing some duplication with the name of the supervisor and other colleagues but without telling them. Now, this is very unlikely to happens, since most journals inform all the authors on the submission quickly. It is however possible that in some cases to avoid other problems, a supervisor will not contact the journal and basically would agree with the submission after asking (or not?). In my opinion, this will be a big mistake… Other possibility, the student will submit a paper alone (without any other co-workers). Then he will embark in solitary in a difficult adventure… and in some cases as happens in other aspects of life, trying to go too fast will end in going nowhere! So, senior scientists are the best medicine against potential self-plagiarism (of course assuming full moral integrity).

Another legal but dubious practice… Although in this case is not unethical per se, I would not recommend you as a beginner scientist to embark in those activities. It is widely practiced… you do countess variations of a problem, with different results, yes; but little, very little interest, but enough to merit another paper in a non very good, but peer-review publication. Doing this will be also bad for you. Remember that more often now, your future career will be jugged more on the impact of your research (citations, invited talks…) than in the actual amount of what you produced. Always, quality will be better than quality.

Be a refined scientist instead of a refined self-plagiarist. So, dear friend… I believe you have the full capabilities to be a refined self-plagiarist. You know what to do, you are probably clever (very clever) and you can work very hard in multiplying your results. Then, my real advice… use all your skills in having a few good and solid papers and use the extra time to keep doing original and interesting research.

Eye pupil shapes (I). To conclude with this rather unusual question and answer entry, some fun... I will be adding to the next posts some examples of pupil shapes in different animals. Let's begin with a (near) SLIT pupil in a really "green" type of frog (picture taken by my son Luis).

And a couple of aerial views… Let me show to you a couple of pictures I took from planes in my recent trip over the Pacific ocean from Australia to California (an interesting and really long trip). Here you have some clouds with early morning light and a view of Sydney city and harbour after take-off.

Yentis, S. (2010). Another kind of ethics: from corrections to retractions Anaesthesia, 65 (12), 1163-1166 DOI: 10.1111/j.1365-2044.2010.06557.x

A new LO•UM web page design: information on our research in Optics at Murcia now better than ever…

2011-08-15T03:35:00.004+02:00

This is going to be a special and short post… simply to announce you that the web page of my laboratory, the “Laboratorio de Optica de la Universidad de Murcia, LO·UM"; has been fully redesigned and is now active on line!

http://lo.um.es

New web page look and same updated content. The main purpose of the LO·UM web page is to provide any interested visitor with all the relevant information on our lab. Our location, members, research projects, open positions, news on the lab and access to all our publications. This site follows the history of our lab and helped with many of the events we organized during the years and to better disseminate our research milestones.

One of the oldest active web page (16 years old!)… perhaps you would be surprised to know that actually this web page is one of the “oldest” permanently active web page in the Murcia region and in the whole Spain. The first active version dated 1995... yes, already 16 years ago. In one of the earliest repertories of web pages, we were the only one mentioned in the Murcia region. I always believed that for a lab in a "peripheral" region of a "peripheral" (scientifically) country... the internet would offer a lot of advantages. So, very soon after I was installed in Murcia in 1994, when web pages were a real "rarity", I asked Ignacio Iglesias to produce the first version. In fact, despite the changes during the years, the main idea and content was already the same then. Looking back in retrospect, we were in this aspect clear pioneers. Many other people included institutional web pages later, but not too many can be proud of having one active and providing useful servicesbeing for visitors for so long!

Many (if not all) different lab members have contributed occasionally to the web page. But I should mention specifically Pedro Prieto. He was instrumental and did a lot of work to have the previous version of the site ready and updated for many years. For this newly redesigned version, Guillermo Pérez and Astrid Luque did a tremendous job. In particular, Astrid has been working in the transference of the information for months. Thanks to all of you.

The creation of a word: LOUM. It is curious that during all these years of presence in the web, our acronym (LOUM) is actually indexed in many different repertories. In Wikipedia (http://en.wikipedia.org/wiki/Loum) or in this encyclopedia, (http://www.nationmaster.com/encyclopedia/Loum), where we are referred as: "The LOUM (Laboratorio de Optica Murcia) in Spain, a major world centre for advanced optics research.)!

Time flies... and yes, 16 years is really a long time. I am personally aware of this because when this page was already active in 1995, my daughter Lucia was not born yet (and she will be 16 years old next November!). The pictures below surely would help to realize the impact of time. The photo on the left is from 2000 in Queensland, Australia (the LOUM web page was already 5 years old) and she was not very happy with that hat... and a photo on the right that I took a couple of weeks ago overlooking Sydney harbour...

Why to worry about the optics of the human eye in the peripheral retina? (...also open PhD positions and expensive bananas!)

2011-08-02T05:05:00.005+02:00

Hello Pablo, I follow some of your posts and I always learn something. Thanks for your time writing this. Now, I have my own question. I understand the importance of measuring the eye’s optics on axis. It is directly related to the quality of vision of a particular person. However, I cannot understand the reason some researchers, including your group, are interested in measuring the properties of the eye off axis, in the peripheral areas of the retina. Outside the fovea, vision is simply limited by the retina and essentially any optics would do basically the same job. Why to worry about the off-axis optics then? Vance. San Francisco, California, USA.

Dear Vance. Thank you for your comments and this very good and interesting question. With this post, I actually resuming the “traditional” type of posts of this blog, based in questions from readers. Your question is actually quite direct… why to be worry about how is the optics of the eye in the periphery? Or why to be worried on how the eye forms the images of peripheral objects, considering our poor resolution peripheral vision?

For readers with less technical expertise, I should say first that the optical properties of any lens get worst when light is coming at larger angles. Most systems are designed to be optimized on axis, and off-axis (oblique) aberrations blur significatively the peripheral areas of the images. Good optical instruments are then designed to keep a reasonable good image quality off-axis. In cheap cameras, it is easy to distinguish this problem. In many pictures you could notice clear distortions appearing at the edges. I am sure you have noticed your gain in weight (fortunately "temporary" due to the optical distortion, so no real...) in a group photo when you were at one side of the group (i.e., your image was formed at an off-axis angle for the lens)… My advice: use a better optics, or try to be always at the central part in a group photo!

So, in general, off-axis optics matters… a lot! And it is extremely important. In fact, it is producing historically headaches to every lens designer. So, why Vance seems to be so sure that in the case of the eye is not that important?

Optics and vision in the periphery of the retina. He is right, at least in his initial, general thinking. In the case of a camera, the resolution of the film (or the electronic chip) is the same all over the sensible area. Then the pictures will show the peripheral blur. However, the human retina has a high spatial resolution in the central part (fovea) that decreases quite fast across the peripheral retina. So, blurred images off-axis would not be distinguished since the resolution of the retina is poor.

I has been intrigued with this problem for many years. In fact, I spent hours and hours doing (seriously tedious) visual experiments in a visit to Andrew Derrington’s lab (at the time at the University of Newcastle, UK). From that research, we published a paper in Vision Research in 1995 (with Andrew, Elisa Colombo and myself as co-authors). In that study, we corrected in part the peripheral optics (defocus and astigmatism) and then we measured grating detection and recognition. At that time, we were very interested in the possible “aliasing” (undersamplig) of gratings when imaged with good optics in the periphery. Artal P, Derrington AM, Colombo E. “Refraction, aliasing, and the absence of motion reversals in peripheral vision.”, Vision Res. 1995 Apr;35(7):939-47.

See retinal images at 40 degrees eccentricity (for different relative defocus) in the right eye of Andrew. Yes, you are right… oblique astigmatism (large) is the dominant aberration.

In fact, having eyes with very good optics could be a problem for the visual system. So, initially, our interest for the peripheral optics was in that direction: a better understanding of the relationship of optics and vision at different eccentricities.

Peripheral optics and… myopia development. More recently, our interest in the optical quality of the eye in the periphery goes beyond the simple scientific curiosity since it was suggested that a relative peripheral hyperopic defocus might drive an eye to grow myopic and this was confirmed in monkey eyes. I devoted an earlier post to this topic: http://pabloartal.blogspot.com/2009/08/can-myopia-progression-be-controlled.html . Future clinical studies to verify this hypothesis in human eyes would require methods and instruments providing fast and reliable measurements of the eye’s peripheral optics.

Measuring the optical quality of the human eye on axis was the first objective of most techniques during the last decades. In fact, to measure the image quality of the eye at different eccentricities was possible, for example, by sequentially using a Hartmann-Shack wavefront sensor when the subject is asked to fixate to a defined location. This type of approach provided useful information on the peripheral optics of the eye, but limited to a relatively small number of angles and after long and tedious experimental sessions.

Measuring the peripheral optics FAST, VERY FAST… We have recently developed a fast scanning peripheral Hartmann-Shack wavefront sensor which is able to measure the eye’s aberrations over a range of 80° of visual angle in less than 2 seconds with an angular resolution of one measurement per degree. This has been recently fully reported in an article published in the journal Optics Express: B. Jaeken, L. Lundström, and P. Artal, "Fast scanning peripheral wave-front sensor for the human eye," Opt. Express 19, 7903-7913 (2011). http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-8-7903 Remember that Optics Express is an open access journal, so you can download this article freely. Bart Jaeken, a PhD student from Belgium in may lab (and also an excellent tri-athlete!), together with Linda Lundstrom (a former post-doc in my lab and now an assistant professor at the Royal Institute of Technology, Stockholm, Sweden) were the co-authors of this amazingly detailed paper.

In the system the high speed and large scanning angle can be reached because the system is based on a rotational movement, keeping the distance between the eye and the instrument equal at all angles. This is a quite significant improvement over previous the sequential systems with a time consuming measuring process and low angular resolution. The new instrument is robust, fast and conformable for the subjects. A wavefront sensor is mounted on a rotational movement stage and while the subject fixates a central spot, a synchronized recording of a series of 80 Hartmann-Shack is obtained in 1.8 seconds. To take the same amount of aberration measurements with a standard static procedure would take about 4 hours (the video clip shows an example of the operation with me as a subject!). The instrument is reasonable compact (see schematic figure) and most components are off the shelf available and is controlled by a conventional laptop computer.

This unique instrument has the capability to be used in a clinical environment for population studies. Due to its characteristics, it is perfectly suitable to be used in the investigation of myopia development and in the design of peripheral optical corrections. It could be used in the future either for basic experiments on the optical properties of a large group of eyes in the periphery as in clinical application where the control or modification of the peripheral eye’s properties are required, such as with different spectacles, contact or intraocular lenses. In fact, Bart is now collecting tons of data in different eyes. When the work is finished, I will report more on that.

OPEN PhD positions in my lab in Murcia, Spain! Interested in doing a PhD in these research topics? If you already have a degree in Physics, Optics, Engineering, etc… and you want to do pioneering work on how the optics of the eye affects how we see… you should have a look on the additional information and apply:

http://lo.um.es/opportunities/Marie%20Curie%20Early%20Stage%20Researcher%20ad_murcia.pdf

Bananas and parking: Australian prices. I am not usually very lucky with currency conversions when I travel or I spend time in a country with a different currency. I remember that when I did a sabbatical in Rochester, NY, in the US in the late 90’s, the US dollar was very strong in relation with the Spanish “pesetas”... our national currency before the euro, and perhaps, if things continue so badly as now our “future” currency again.. (I hope this will not be the case!). Now, in Australia, I experienced again a similar situation. The Australian dollar never was so strong as compared with the euro as is now: 1 Euro is “only” 1.3 Australian dollars! Because I am using my Euros to live here… I really would like to have a stronger Euro… and, yes, everything seems to be very expensive here in Sydney. But, if I have to select two partcular items that are just incredibly expensive: bananas (around 15 dollar per kilo), I suppose 10 times more expensive than in Spain (at least I do not like very much bananas…) and car parking in the city… (as ridiculous as in some cases 24 dollars each half an hour!). The good thing… incredible beautiful views of Sydney are not as expensive (of course it depends on where you parked).

Jaeken, B., Lundström, L., & Artal, P. (2011). Fast scanning peripheral wave-front sensor for the human eye Optics Express, 19 (8) DOI: 10.1364/OE.19.007903

3rd anniversary post

2011-07-12T08:17:00.006+02:00

Yes, it is hard to believe, but this blog is already 3 years old. The first entry was posted on July 12, 2008. I remember well I did this in a very hot night in my house near Murcia city (the area I live there is called Altorreal). Now, I am writing this anniversary entry in a sunny winter day in Sydney. Many things happened in these three years. And actually, today was not precisely a good day for me… I had my first Australian parking ticket… and I learn why every street corner was available to park… and I had a flat tire in the car the Institute offered to me for these first days. All happens in the same morning... so, I am glad is over. Well, now all this is solved (paid ticket and changed tire…).

Greetings pictures: coma. Instead of celebrating the anniversary with a picture of a cake with 3 candles, I found more appropriate this “analogical” (not computer simulated, so real…) pictures of coma, in form of both a point spread function and interferogram. They are really nice, do not you think? These pictures are from the old (nearly 50 years old) book: “Atlas of optical phenomena”, by Cagnet, Francon and Thrierr. They are very nice, remember, actually produced and recorded in the dark room! For the non specialists, coma is a defect (aberration) presents in optical systems that produce distorted images. In this particular case, the image of a point has a distinctive comatic shape (and that is the reason for the name!).

Some facts about the blog: 59 entries, including this one, so about 20 per year. I believe this was worth the effort. The blog is known and appreciated, not only by scientists in visual optics, also by independent readers. I also used the blog recently to report a nearly live coverage of the two meetings we had in June. Some of the posts related to careers in science were reproduced in the Optical Society of America blog: “Bright Futures”.http://www.osa-opn.org/BrightFuturesBlog/post/Tips-for-Having-a-Successful-Career-in-Science.aspx

The most important… this has been a way of communication with many people around the world. And I hope some of the information has been useful. To maintain a reputation that all data presented here are solid and based in the best scientific evidence is the key. Of course, there are also a lot of personal opinions on many different aspects. I hope is clearly separated and every reader knows exactly what type of information is reading here.

The most successful post... yes, you may already know. The definition of angle kappa in the eye! http://pabloartal.blogspot.com/2008/08/on-definition-of-angle-kappa.html This was one the first posts, and because there is a lot of confusion on ocular axis definitions, it clearly became (and still is like that now) the number one visited post! In this line, I will prepare a future post with some useful numbers...

The post I like more... well, it is difficult to select just one, but the one devoted to my (personal) rule of 8% can be one. http://pabloartal.blogspot.com/2010/03/empirical-rule-of-8.html

Some comments from people that apparently felt themselves indentified was a curiosity. If you miss then, I am sure you will enjoy it (either if you are in the 8% or 92% groups). This number (8%) generated some discussions with different colleagues. Some suggested that 10% (fraction of people you will find that you should not trust) would be more accurate than my 8%. To be honest, I confess that there little science behind my number…

Comments. I know I have much more readers that people that actually decided to send some comment. In any case, I keep welcoming your comments even if they are not nice to me. I still value, although I do not agree, that “friend” that simply post anonymously that everything here was basically self-promotion materials, a kind a perpetual advertisement. The person asked me to stop writing such a poor blog. So far, I did not consider seriously his advice... and this keeps alive!

Awards. I am not actually writing this thinking in any awards. I am not a professional science writer. I am a professor and a scientist and I only dedicate to this work some extra time in a very un-professional manner. So, I know I cannot compete with a plethora of spectacular professional science blogs out there. However, the value of this type of personal blog is that I can give the real scientists perspective that professional writers would miss in general. In any case, this was selected as finalist in the “Research blogging”, http://researchblogging.org,specialized science blogs. Some of these entries are posted there.

Name. Yes, this blogs was initially called “Optics Confidential” and later became simply “Pablo Artal blog”. Why I changed the name? it is easier to identify the blog with me now, but the main reason was that I liked initially the first name, but with time, it seemed not the best name, so I changed…

Something I wanted to cover, but I did not (yet). Not really… perhaps I suggested a few times to write about the Spanish economical and political situation, but finally I did not. Also some readers asked me for more details on my private live, but I supposed that was not of real interest for most people… In any case, you already have lots of pieces of information on my personal live in the posts. A nice anecdote… in a recent radio interview, the journalist knew where I was because the blog. So it was an odd moment since to make things easier I did not tell them I was not in Spain at the time of the interview. What also happens some time is that if I meet somebody in a conference, when I start talking about something that happened to me… he already knew it (yes, because it was reported in the blog). So, my conversations are now even more boring (for those friends reading these posts).

A new blog. A companion blog just commenced. I called “The other blog of Pablo Artal”. The name itself is an indication that this will be the primary, most important blog. The other http://visiondelejos.blogspot.com/ will be in Spanish and I hope it will be simply complementary. As you can imagine, I am much better writing in Spanish than in English (obviously...). In that line, some of my critics were mentioning my poor English here in this blog. Sorry for that, I know it should be better and I will try. But, for me (a non professional writer...), English is the "lingua franca" and although we should try our best, I ask English speakers readers to be nice with me on this... and if something is really bad or make cause some confusion, please let me know. I would really appreciate.

And finally, please have fun and enjoy the summer (if you are in the north). I hope you will keep reading this during the next coming years… and greetings from the south winter!

My best regards, Pablo

A new companion blog: "Vision de lejos. El otro blog de Pablo Artal"

2011-07-07T11:36:00.008+02:00

I decided to begin a new blog as a complement to this one. It will be in Spanish and with a more general scope. The name: VISION DE LEJOS. EL OTRO BLOG DE PABLO ARTAL (Far vision. The other Pablo Artal blog!): http://visiondelejos.blogspot.com/

Of course, this blog (http://pabloartal.blogspot.com) that will be 3 years old in a few days, will continue better than ever!

Sabbatical in Sydney, my new home 17000 km south-est Murcia…

2011-07-02T15:33:00.009+02:00

Some of you probably knew that I was planning a sabbatical year in Sydney, Australia. Since time is really flying… that moment is already here! I arrived to Sydney last Wednesday after a long (although relatively smooth) trip via Bangkok.

Views of Bangkok airport and the Australian land in my way to Sydney... and my silhouette with the Sydney bridge

I will be at the BrienHolden Vision Research Institute of the University of New South Wales (UNSW) (http://www.brienholdenvision.org/research). During the next 12 months, I will collaborate with Arthur Ho's group on different aspects of the possible optical control of myopia. This is a topic we have been interested for several years in relation with the optical properties of the eye in the periphery of the retina: http://pabloartal.blogspot.com/2009/08/can-myopia-progression-be-controlled.html).

Of course, during this year I will continue with all the different projects that are in progress in my lab in Murcia… and also I hope to have time to explore and discover this part of the world. This is my second time in Sydney. I was here before in the year 2000 (when I did a short time visit to the Quensland University of Technology in Brisbane). This is a remote (for us in Europe!) location, but very attractive. You can really feel the distance... Early this week, still being in Spain, I suffered quite extreme hot temperatures, so now the Sydney winter (quite mild in any case) is very welcome. Surely, I would need some time to adapt to several of the differences:

- the “wrong” side driving

- the 8 hours ahead and the feeling of distance (today reduced by Skype, of course…)

- seeing so many people without shoes…

- to notice that most people is in better shape than you and than most people is younger than you!

You know that Sydney is great city, perhaps one the most beautiful cities in the world. I noticed this time (ten years after my first visit) that the city is more multicultural, with a large diversity of people from all over the world.

Eternal good views (walk from Coogee to Bondi beaches) and a Sydney winter beach day (it is amazing how many people is swimming in July here, what is the European equivalent of January!).

The UNSW has a compact campus located in a Sydney eastern suburb. I am living in a nice house (probably from the 40’s) at a walking distance from the campus in Randwick. And some famous beaches are nearby (Coogee and Bondi beaches). I hope all this nature and entertainments distraction will not prevent me of hard work!

UNSW campus and Coogee beach

You can consider this as a special post, just to announce the new situation of my sabbatical. However, this in fact following a series of also unusual posts related to the two meetings I organized in June: AOIM (http://pabloartal.blogspot.com/2011/06/live-reporting-on-8th-international.html) and EEIII (http://pabloartal.blogspot.com/2011/06/live-reporting-on-engineering-eye-iii.html). Actually, June was a very busy, busy... nearly chaotic month. So, I am glad it is over now and everything went really well.

And... an interesting interview to Pablo Artal today at RADIO EXTERIOR DE ESPAÑA. It is amazing that because this blog, the radio journalist, Alberto Martinez, cleverly discovered that I was already in Sydney! Listen...
http://www.rtve.es/alacarta/audios/puntos-de-vista/puntos-vista-pablo-artal-catedratico-fisica-optica/1145824/

AND A JOKE from Jay Pepose, a Professor of Clinical Ophthalmology at the Washington University School of Medicine in St. Louis, Missouri, USA. Jay anticipated my possible transformation in Australia as "Pablo Dundee" (hard to believe specially considering the muscles...).

I will resume (I hope soon) the normal type of posts of this blog. I have already several questions and topics to be covered.

And, by the way, the 3rd anniversary of this blog will occur in a few days (12 July 2011).

Greetings from Sydney!

Two of my old newspaper articles on the history of visual optics and the situation of physics

2011-06-21T19:00:00.004+02:00

Pablo. I am really enjoyed your recent opinion article in "El Pais" newspaper on the situation of science in the Spanish universities. I wonder if you published something else in the past on any related topic. A style for a general public would be prefered. Of course, spanish is ok for me. Angelo, Miami, USA.

Angelo, thank you for your interest. Yes, in addition to the recent article in "El Pais" that you already knew (http://www.elpais.com/articulo/sociedad/Universidades/ciencia/ranking/Somos/realmente/malos/elpepusocedu/20110607elpepusoc_8/Tes), I published one with Susana Marcos decribing the history of Physiological Optics in Spain. This apereared in the same newspaper in 2006. Here you have copy:

And before that, I explored the situation of physics in another article that still you can find on line the "El Pais" web site: http://www.elpais.com/articulo/futuro/fisica/ciencia/peligro/elpepisupfut/20050202elpepifut_5/Tes

And yes... these three articles were in Spanish and I hope quite easy to read for any educated person.

And talking about the newspaper "El Pais", Malen Ruiz de Elvira a science journalist has published a nice article reporting on the EEIII meeting. You have the link below:

http://www.elpais.com/articulo/futuro/ojo/maquina/tuneable/elpepufut/20110629elpepifut_1/Tes

and a copy of the actual paper...

LIVE REPORTING on the Engineering the Eye III (EEIII) from Benasque, Aragon Pyrenees , Spain

2011-06-10T12:11:00.015+02:00

Friday 10 June, 11:00 am.

“Engineering the Eye III” (EEIII) has just started a couple of hours ago in Benasque. I am quite happy to welcome to this fantastic location all the participants: 100 scientists that travelled long distances to be here.

Some of the attendees were also attending the AOIM meeting in Murcia earlier this week. They were the most fortunate since they enjoyed the best of both meetings. For those not attending the Murcia meeting, you can visit a summary of what happened there:

http://pabloartal.blogspot.com/2011/06/live-reporting-on-8th-international.html

But, let’s now focus on EEIII. This is a high quality and unique scientific meeting dealing with aspects of the Physics and Engineering of the human eye. This meeting is the third in a series that started in Rochester (USA) (organized by David Williams) and Galway (Ireland) (organized by Chris Dainty). Both, David and Chris joined me as the organizer to this EEIII.

EEIII enjoys the fantastic facilities of the “Centro de Ciencias de Benasque”.

Friday 10 June, 12:30 am.

First pictures of the opening of EEIII by the organizers, David Williams, Chris Dainty & Pablo Artal. (Iphone photos provided by Guillermo Perez).

Friday 10 June, 8:00 am.

Sorry... too busy during the whole day to keep this page updated. Too many things going on and so interesting! I promise I will keep you updated later on what happened today. Now, after two sessions dedicated to imaging and treatment with femtosecond lasers... is time for the poster session and the reception.

This is the group photo:

Sunday 12 June, 11:00 am.

YES, I know you were waiting for some information yesterday but nothing happened! Sorry... I had not anyl time... What happened yesterday here at EEIII in Benasque? During the morning we completed the excursion from La Besurta area to the Forau de Aigualluts and beyond. We were really lucky and the weather was good enough to have a great walk. You can see below some pictures of some parts of this nice morning.

Unfortunately, David Williams had a an accident and he had to return to the village. In this picture, he is with Jennifer Hunter minutes before that happened. I am happy to inform that David is recovering well and he is already now in the session.

One important moment of our walk was when we arrived near to the first patch of snow. Then Austing Roorda from University of Berkeley and a canadian... quickly run to the snow and wrote the EEIII logo on the snow (including the eye). See picture, the snow logo is on the right.

Austin (below) is returning to the path...

And we arrived to the Forau...

and continued to Collado del Toro...

We were lucky and Aneto (the highest peak in the Pyrenees) appeared suddenly...

We finalized after the 4 hours walk with a nice lunch at the Hospital de Benasque

(http://www.llanosdelhospital.com/)

Sunday 12 June, 3:00 pm.

But, what about the science in the meeting? Plenty of interesting, exciting and new things. It is amazing to see what can be done now in the lab as compared with 20 years ago. What a long way we walked!

Two topics were the main of the meeting: Two-photon techniques and adaptive optics. Yesterday we also had a session on classical issues in visual optics.
Now the last session of the meeting is starting.

Sunday 12 June, 4:00 pm.

Trying to recover some time in this reporting... I am writing now during the last session. Later today, we will also have an unique event. A concert by pianist Saya (by the way the piano is already in the room in the second floor!).
The first day of the meeting (Friday) was mostly devoted to applications of 2photon techniques both for imaging, treatment or manipulation. I am convinced that 2photon techniques will be playing a very important role in many aspects of ophthalmology in the next decades. Let's wait!

But, what are 2photon techniques? A simplified answer... Under normal 1photon absorption, one photon (typically a UV photon) would be absorbed in a medium (for instance tissue in the cornea or the retina). The same energy level in the same medium could eventually absorb TWO photons of double wavelength (half energy) corresponding to IR light. There are many advantages when this happens, IR light seems to be better suited for biological imaging as compared to UV, and also because the 2photon process has a very low probability, we would need a very high density of photons. This can be obtained using femtosecond lasers. An additional bonus is that this process will only occur at the very localized spatial area where the laser is very well focused. So confocality and optical sectioning would occur naturally...
Josef Bille (Heidelberg) and James Jester (Irvine, USA) talked first on 2photon imaging of the retina and the cornea respectively.

... and Tuesday 21 June.

The meeting was so intense and interesting that... of course, I had no time to report on the details of the presentations and discussions.

And more than a week later, I prefer to simply close this post with some additional videos and photos.

From a scientific point of view, there was tons of interesting issues discussed. I will cover some of them soon in future posts. Enjoy now some interesting material below...

FOOSBALL... During the nights pf the meeting some were ansxious looking for a couple of bars on town with this exciting activity.
This video features Pablo Artal and Jose Ignacio Latorre playing against some locals...

A concert to celebrate the end of EEIII...

And even a "Happy birthday" celebration... Two of the organizers, David Williams and Pablo Artal, celebrated their birthday during the meeting...

AND FINAL THANKS TO ALL THE PARTICIPANTS IN THE MEETING. YOU ALL WERE THE RESPONSIBLES FOR A GREAT AND UNIQUE EVENT!

Wednesday 29 June 2011.

Malen Ruiz de Elvira a science journalist has published a nice article on the EEIII meeting in "El Pais", the leading spanish newspaper.

http://www.elpais.com/articulo/futuro/ojo/maquina/tuneable/elpepufut/20110629elpepifut_1/Tes

Info added November 2011:

Abstracts of the EEIII are now available to download and cite at:

http://congresos.um.es/eye/eye2011

Spanish universities and science… are we as bad as the ranking are showing?

2011-06-08T18:47:00.001+02:00

Perhaps some of you can be interested in an opinion article that I published today on the situation of scientific research in the Spanish universities in "EL PAIS", the Spain’s leading newspaper (In Spanish).

You have the link here:

http://www.elpais.com/articulo/sociedad/Universidades/ciencia/ranking/Somos/realmente/malos/elpepusoc/20110607elpepusoc_8/Tes

LIVE REPORTING on the 8th International Workshop on Adaptive Optics for Industry and Medicine (AOIM) from Murcia

2011-06-05T12:59:00.036+02:00

Prof Artal, for personal reasons I was not able to attend the adaptive optics meeting you are organizing in Murcia. Perhaps you could provide me and other interested readers of your blog with some information on this event. Hans, The Netherlands.

Yes, for Hans and anybody interested, I will be providing with information on the AOIM meeting in this post, the first of this blog that will not be completed at the moment of posting (in this case until the meeting is finished on Wednesday). So, this will be an opeen post... Of course, this is not the same as attending the meeting here in Murcia… but at least you could have some flavor of what is going on.

http://lo.um.es/events/aoim2011/AOIM2011.html

NEW (and better quality) PHOTOS AT THE BOTTOM OF THIS POST. DO NOT MISS!!!!!!!!!

Sunday 5 June, 1 pm

Beautiful sunny day in Murcia (now 23 degrees) to welcome the meeting delegates.

Access to meeting abstracts (AOIM droplets, nicely prepared by Pedro Prieto) is already available at: http://congresos.um.es/aoim/aoim2011/

Sunday 5 June, 4 pm

First (anonymous) delegate with the official AOIM t-shirt!
Do not miss tonight the reception at 8:30 pm at the 7 Coronas hotel in the center of Murcia city. http://www.hoteles-silken.com/hotel-siete-coronas-murcia/

Sunday 5 June, 11 pm
Spanish food (tortillas, calamari, gazpacho, gambas...) and drinks at the welcome reception. Good company, talking about jet lag (the good thing of not travelling overseas for a meeting, it is avoiding jet lag!) and good weather... in preparation for tomorrow' official opening of the meeting at 9:15 am!

Monday 6 June, 11 am

We are on! The meeting was officially opened by the rector of the University of Murcia, Prof. Jose Antonio Cobacho, the vicerectors for research, Profs. Juan Maria Vazquez and Gaspar Ros and the chair of the program committee (this reporter, Pablo Artal). See picture below of the official opening of AOIM.

AOIM is featured at the main University of Murcia web page today (as well as in several local newspapers). And... flags in the meeting auditorium!

The first session, chaired by Alexis Kudryashov on AO for high power lasers is now under way. Luis Roso, from Salamanca and Sven Verpoort from Munster are the invited speakers for this interesting session.

Monday 6 June, 10 pm

Luis Roso opened the meeting with an exciting talk describing the potential (in some cases near to science fiction!) of extremely high power lasers. PettaWatt lasers would required dedicated AO. These are good news for our field. Without good AO those enormous power would not be possible. The future is approaching!

Sven Verpoort showed the path for this type of applications. A new design of unimorph deformable mirror for high power lasers. After the first coffee break, Andrew Forbes from CSIR in Pretoria (South Africa) described the potential of liquid crystal spatial light modulators. The applications for vortices were really beautiful. The versatility of these devices is really remarkable. Pedro Prieto followed on this topic. The pros and cons of SLMs compared with mirrors were discussed. After some polemics, most people probably agreed that SLMs and DMs are more complementary, than competing technologies for AO. Ulrich Wittrock chaired this second session (see his silhouette below!).

In the afternoon session, Askan Arianpour from UC San Diego showed the nice capabilities of fluidic lenses with huge dioptric range. Real applications for zoom imaging systems in minimally invasive surgery were shown. Juanma Bueno chaired this session (photo below with Askan).

A lively poster session followed by a reception on site completed this long and exciting day. (of course, this picture was taken when everybody was attending the session!). More to learn tomorrow!

Program committee members, Gordon Love, Sergio Restaino and Alexis Kudryashov seems to be paying attention to the presentations.

And a vodka gift from Russia...

Tuesday 7 June, 8:00 am.

The second day of the meeting is about to start. The morning session dedicated to deformable mirrors and control strategies. After lunch, industry will have time to show the most recent advances. Alpao, Adaptica, Thorlabs, Boston Micromachines, Zeiss, Scimeasure and Voptica are represented in the meeting. (See Voptica booth with Guillermo Perez).

Tuesday 7 June, 11:00 am.

The session on deformable mirrors is now in progress. Check the abstract web page for details on interesting new ideas: a photocontrolled DM, a liquid DM... Sergio Restaino, from Albuquerque, USA, is chairing this session.

Tuesday 7 June, 3:00 pm.

The session on wavefront sensors chaired by Gordon Love, Durham, UK, was full of nice results. Sergio Restaino presented an invited overview on his AO-test bed. Diego Rativa, Dublin, showed an idea for using photonic crystal fibres as wavefront sensor. Quite interesting, but perhaps still far from a real application. Although some questions and interesting discussions on the limitations of the Hartmann-Shack wavefront sensor are always present in every meeting (and this is not, of course an exception), today this is a fantastic tool, robust and well adapted for most problems. The simplicity of the Hartmann-Shack sensor renders this practically unbeatable today (of course, this is only in my opinion!). Now, the industrial session is in progress. A good oportunity to learn more about the recent products of the leading world companies that are here in Murcia. Josua Fernandez is the chair of this special session.

Wednesday 8 June, 9:00 am.

Not too many people in the room yet… probably they are still recovering from last night conference dinner. This was in Lopagan, a small village at the Mar Menor, after a visit to the Cartagena roman theater and a short boat cruise from La Manga to Lopagan. Although it was (unusually) raining in Murcia city, the conference attendees were able to complete the excursion more or less dry! See picture below of the boat arriving to Lopagan ready for the dinner.

Great food at the restaurant at the “Club nautico”. I believe most people enjoyed the “Dorada a la sal” and the calamari. Program committee members, Chris Dainty (Galway, Ireland), Ulrich Wittrock and Pablo Artal at a moment during the dinner. Gordon Love at the other side of the table took this picture.

Wednesday 8 June, 11:30 am.

The first session of the morning chaired by Ignacio Iglesias on AO microscopy was really excellent. Beautiful 3D images of AO guided microfabrication were showed by Martin Booth (Oxford, UK) in his invited presentation.

After the group photo (I will tell you more later on the difficulties to find a proper spot...), now the session on AO vision science is just starting.

Wednesday 8 June, 4:00 pm.

The group is now visiting our laboratories at LOUM. In a few minutes, the final session of the meeting will start. Sadly, we are really reaching the end of the meeting! Three intense days of AO science and applications!

The final session is chaired by Chris Dainty (by the way, the current president of the Optical Society of America). Talks by Michel Verhaehen (Delf, Holland), Manuel Cagigal (Santander) and Gouquiang Li (Sant Louis, USA) will complete the meeting. Well, not completely... we still have the presentation of Andrew Forbes on the possible venue for the next meeing, the 9 AOIM: South Africa!

Wednesday 8 June, 6:30 pm.

The meeting is over! THANKS TO ALL THE PARTICIPANTS!

See you in South Africa in 2013!

Some more pictures (including the group photo) will be added later.

My best regards to all, Pablo

Tuesday June 14. NEW (and better quality!) PHOTOS HERE!!!!!!!!!!!!!!!!!!

AOIM 8 GROUP PHOTO!!!!!!!!!!!!!!!!!!!!!!!!!

Wave... group photo

Official opening of 8AOIM!!

Alexis and Pablo opening the first session of AOIM8.

Glare or blur? scatter or aberrations? How these optical effects actually degrade vision?

2011-05-31T00:22:00.006+02:00

Prof Artal, I was quite fascinated by your video demonstration of the optical simulation of what a person sees. My question is if you can go further and show the differences between glare effects and those related to aberrations. I am 71 and now having difficulty with night driving because of star burst glare. I ordered glasses with wavefront correction hoping this would ease the glare problem. However, they performed little if any better than my original glasses with only astigmatism and myopia corrections. The causes of star burst glare in the older eye may be well known but I have not been able to find any information. Paul B. USA.

Paul pointed out here a very important issue typically not well understood by the general public… but even in some cases also confusing for eye care professionals. I will try to further explain the differences between aberrations and scatter in the retinal image and their relative impact in vision. In fact, I already covered this problem in different previous post, but now I will try to answer Paul’s specific question in more detail. Optical aberrations and intraocular scattering in the eye are two different phenomenon causing different effects inthe retinal image and in visual quality. They can be somehow related or not. During normal aging, both aberrations and scatter increases. Typically, increased aberrations produce blur and higher scatter induces glare and a reduction in contrast at the retinal image. The actual situation in the eye is that both optical factors appear together with more or less intensity.

These pictures below graphically explain how both aberrations and scatter affect the retinal image. These are slides that I have been using for my teaching and lecture presentations for many years. In fact, I used a picture of my daughter Lucia when she was a little girl (as an indication of how fast time is passing… she is now taller than me and 15 years old!).

An increase in aberrations, including defocus (myopia or hyperopia) and astigmatism blur the retina images. If the blur is caused by defocus and astigmatism, it can be corrected with spectacles and/or contact lenses. If the main degradation is caused by higher order aberrations blur could not be corrected by conventional means. Several approaches, such as surgery or specialized wavefront spectacles has been proposed, but in my opinion this methods are not practical. As I have mentioned here in several occasions, higher order aberrations can be corrected in the laboratory.

A larger amount of scatter in the eye induce a reduction of contrast in the retinal image, although the details in the image are not necessary lost (as happens with the effect of blur). Glare disturbances are a direct consequence of an elevated scatter. Severe scatter produced by cataracts is solved with surgery. Smaller amount of scatter associated with normal aging cannot be corrected.

And of course, the real situation in every eye is that both aberrations and scatter are acting together, inducing some blur and some contrast reduction.

We also demonstrated an interesting relationship between aberrations and scatter: they could be somehow coupled (see a more detailed previous post: http://pabloartal.blogspot.com/2009/03/scatter-and-spherical-aberration-good.html).

In the future, the optimum approach will be to measure objectively in each eye both aberrations and scatter. Measuring aberrations is nearly a routine now using wavefront sensors. Measuring scatter is more complicated. We tried many years ago with direct recording of double pass images. This is a good approach when the amount of scatter is relatively elevated (actually we proposed a method to classify the severity of cataracts: http://pabloartal.blogspot.com/2011/02/how-can-i-know-if-i-have-cataracts-and.html). We are now working in a more sophisticated approach to determine objectively minor changes of scatter. I will keep you informed in the future developments of this research, that hopefully would help practicioners to actually detect elevated scatter.

In summary, the optical quality of the retinal image is affected together but “differently” by two factors: aberrations causing blur and scatter causing glare. In some cases, one is predominant, for instance, blur in a myopic young eye, or glare in an emmetropic older eye with early cataracts.

In a week… AOIM 8, from Russia to Murcia. In just a week, we will have here in Murcia more than 150 delegates from many countries attending the international workshop on adaptive optics in industry and medicine. It promises to be an exciting event… I will report you on the main finding of the meetings. Interestingly, delegates will be able to arrive the Campus de Espinardo from the city center by tram. The new line is finally open just on time for our meeting!

An interview... opinions and some facts. Perhaps you are interested to read this interview recently published in the PRINUM web page covering research news of the Murcia University (in Spanish). http://www.um.es/prinum/index.php?opc=entrevistas&ver=39

A palm tree in front of our building. The view of our building on campus changed after we planted a 10 meters palm tree last week. Unfortunately, it seems that the palm tree will not survive… (I avoid you the picture now, but I will keep you posted…).

Lorca earthquake. In a recent post, I mentioned my condolences to the Japanese people for the terrible earthquake and tsunami they suffered. A few days ago, we also had an earthquake very near, affecting mainly the town of Lorca about 70 km from the city of Murcia. Although the earthquake was not very strong (5.3), there was a lot of damage in that town and 9 persons were killed. I was in the lab (it was around 7 pm) and I noticed clearly a strong vibration of my office. We did not have any damage, although some of our optical systems lost their fine alignment. I would like to thank friend and colleagues interested in our conditions when they knew about the earthquake in the international news.

Murcia optics lab research at ARVO, vintage 2011

2011-04-25T11:58:00.006+02:00

Dear Prof. Artal. I am PhD student working in vision research and I will be attending the ARVO meeting for the first time next week. What you think I should not miss? Perhaps you can recommend some of your own presentations? A. London. England.

As you probably already heard, ARVO is a quite large scientific meeting covering broad aspects of Vision research and Ophthalmology. So, it is difficult to recommend you something specific. However, I can point out what we will be presenting there. Lots of exciting stuff that I am sure you will enjoy! I hope I will see you there…

But first, I will tell something about ARVO for those readers not so familiar with this meeting. ARVO is the acronym for the Association for research in Vision and Ophthalmology (www.arvo.org), the scientific society organizing this large and famous scientific meeting in vision research and ophthalmology. The ARVO annual meeting is held every late April/early May in Fort Lauderdale, Florida (USA). Unfortunately, the meeting will move in 2013 to a different location. I am afraid this was a very bad decision from the ARVO management and would probably kill the main charm and characteristics of the meeting. I believe this is the typical decision than organizations make without considering what their members prefer! The meeting in the current location is fantastic for students to attend and to present their research. It is very informal and usually combined with beach parties after the hard work in the conference center. In a future location, such as Seattle, I am afraid this atmosphere will be definitively lost. And for us, Europeans, the relatively easy access through Miami and the inexpensive motel prices in the Fort Lauderdale area will also disappear! Nothing last forever!

In any case, for this year 2011, we still have the opportunity to enjoy a real ARVO meeting and of course some of our recent research: vintage 2011!

To facilitate your navigation through the convention center at correct times, I will mention our contributions in chronological order.

On Sunday May 1^st, the first day of the meeting, Eva Acosta, a long term collaborator of the lab, and now in a sabbatical year at the University of Arizona in Tucson, will present a poster with results on aberrations of isolated human crystalline lenses measured with an interferometric method (with a very high precision). The evaluation of what are the most important aberrations, with special interest in the asymmetric terms will be discussed. These results provide a better insight into the aberration structure of the human crystalline lens. See picture with a real human crystalline lens and interferogram.

In the aberrations poster’s session on Tuesday 2^nd morning, you cannot miss Juan Tabernero’s poster describing a sophisticated optical modeling in real eyes of the effect of a small aperture to increase depth of focus (the AcuFocus corneal inlay). Although this is a simple and effective solution to increase near vision, Juan offered some important clues for better optical outcomes. In eyes with small astigmatism and aberrations the optimum centration of the aperture was near the corneal reflex position. For improved optical outcomes, some small residual myopia and correction of corneal astigmatism might be required.

We will have a prominent presence in the Wednesday 3^rd afternoon session on peripheral refractive errors. First, Bart Jaeken will be presenting our exciting new results of high resolution peripheral refraction and aberrations in a large population. We have been using a new and unique instrument: the scanner peripheral Hartmann-Shack wavefront sensor (see video of the operation below). This system allows to measure refraction and aberrations every one degree for 80 degrees of visual field in a couple of seconds with very large accuracy. I believe this system will play an important role in better understanding peripheral optics (Watch for a future post dedicated to this issue very soon).

The role of peripheral optics in myopia development is still a controversial issue. If actually controlling peripheral optics con affect the development of myopia we will need instruments like the peripheral scanner and devices to manipulate the off-axis optics. In the same session. Linda Lundstrom, a former post doc in my lab, and since them a collaborator will describe how several commercially available contact lenses actually modify the peripheral refraction. A presentation full of interesting practical details for those interested in the practical control of myopia manipulating the off-axis optics.

Also on Wednesday, in the 3:45 session on the effect of optical blur on vision, we will have a couple of talks you should not miss. Christina Schwarz will be using our binocular adaptive optics vision analyzer (http://pabloartal.blogspot.com/2009/08/binocular-adaptive-optics-simulator.html) to evaluate in a non-invasive manner the effect of the small-aperture concept (AcuFocus inlay) to increase depth of focus. This talk nicely complement Juan’s poster with the optical predictions. In the same session, I will be describing some exciting results on night myopia). In summary, we used a modified adaptive optics instrument with invisible measuring light to re-evaluate the phenomenon of night myopia. We found large individual variability and an average modest (less than 1 D) myopic shift for low light conditions. We confirmed that the main underlying reason for night myopia is the accommodation shift occurring for low light levels. Chromatic and high order monochromatic aberrations have a minor effect in this mechanism. (I also promise a full post on this topic soon).

The last day of the meeting (Thursday 4th) will be also very busy for us. A pity that some people that usually start returning home that day will miss them. As a recommendation, do not miss Thursday. Some of the most interesting optical papers and poster are actually scheduled that day (perhaps to convince attendee not to leave!). For Europeans with most flights departing in the evening that day it would not be a problem. In the morning sessions, we have will present some of our highlight in the meeting.

Our new approach to measure objectively scatter light in the eye. Measuring intraocular scatter is like a “last frontier” in visual optics. I have been personally interested in this topic since a long time. We have recently described an optical standard double pass method to be applied to detect cataracts (http://pabloartal.blogspot.com/2011/02/how-can-i-know-if-i-have-cataracts-and.html). But now, we have gone much more further! Haris Ginis, a friend and collaborator) from the University of Crete that spent several months in my lab recently, will describe a clever approach to register the wide-angle PSF in the living eye. A little bit complicated to describe the full procedure here, but in summary, series of disks with different diameters were projected onto the retina and the images recorded. With appropriate processing, we were able to reconstruct PSFs up to 10 degrees of eccentricity with an intensity dynamic range of more than 6 orders. Impressive? Wait until you see the results. (See picture of Haris with a scatter halo from a light bulb and a few beers!).

In the same session, Guillermo Perez will present an extension of the same instrument operating with different wavelengths. We were able to separate out the different scatter contributions (for different colors) from different ocular structures.

As some readers already know, we have been working during the last years to improve the performance of light adjustable intraocular lenses (LALs) (http://pabloartal.blogspot.com/2009/04/light-adjustable-intraocular-lenses.html). In the Thursday morning poster session, we will present to interesting poster on the continuation of this study. Encarna Alcon will show the latest results on how we can induce negative spherical aberration in these lenses to increase depth of focus. Amazing good results providing patients with good vision at most distances. In a companion poster, Ines Yago, a resident in ophthalmology at the Hospital Virgen de la Arrixaca will show how we used the LAL to optimize the refractive and aberration outcomes in post-LASIK cataract patients. This type of adjustable technology is especially well suited for these type of patients who may present large refractive surprises and have large corneal aberrations induced by the previous LASIK procedures.

In the same session, Carmen Cánovas, a former PhD student in my lab, and now an employee of AMO in Groningen (Holland) will describe an interesting and complementary study. She used ray-tracing approaches to improve IOL power predictions for myopic post-Lasik patients.

And finally, Juanma Bueno, will present some impressive images of multiphoton microscopy (http://pabloartal.blogspot.com/2009/05/ultrafast-lasers-to-see-and-treat-eye.html) applied to study the retina in chicks. This is an ongoing project in collaboration with Frank Schaeffel aimed to better understand the changes in the retina during myopia induction in chicks (a widely used animal model in myopia research). As an appetitive, see a 2-photon 3D reconstruction of the normal chick retina and wait for Juanma’s talk for more amazing images.

I hope you enjoy these contributions and the meeting. See you in Fort Lauderdale!

And if you want to know more about the Murcia Optics Lab... have a look to this video in Youtube:

(Version de este video en español: http://www.youtube.com/watch?v=F4NK_nVGwzw)

The optics of the eye in old people is not as bad as you would think…

2011-03-15T20:27:00.005+01:00

Dear Pablo. I would like to know how the human eye, after all an optical instrument made of living tissue, is still working relatively well in people as old as me (turning 80 years old soon…). Andres, Seville, Spain (original question received in Spanish).

Dear Andres, I am happy to have senior readers as you interested in these infrequent posts… and I fully agree with you. It is rather remarkable that an optical system made of biological tissues, such as our eye, is still properly working in many cases after a very long time… This a question I specially like, since I have been interested in the topic of how and why the eye changes during normal aging. We know now more details that I can share with all of you here. But I can advance something… similarly as with other functional capabilities, there are many balances and compromises that renders the eye’s optics quite practical even when we get older.

What... you do not agree? Well… please, keep reading before complaining (if you are an older reader) on all the “disasters” that may occur in your eyes when you are getting older. It is true that after a continuous declining, at the age of around 45 years old, we all note the effect of presbyopia. This is the lack of a functioning accommodation mechanism. Near objects cannot be at clear focus and we need to use reading glasses or other possible solutions (this can be the topic of a future post). Another common age related issue (and recently mentioned here: http://pabloartal.blogspot.com/2011/02/how-can-i-know-if-i-have-cataracts-and.html) is cataract. The crystalline lens suffer a progressive degradation inducing more light scattering reducing the contrast in the retinal images and obviously impairing vision. The solution is a simple and the most common surgery today: removing the cataractous lens and placing an artificial intraocular lens instead. Some recent innovative alternatives have been already discussed here before (http://pabloartal.blogspot.com/2009/04/light-adjustable-intraocular-lenses.html).

Well, sure, these two problems (presbyopia and cataracts) are serious, but be prepared to know the good news too. Normal aging affects in many different aspects our visual system. For example, spatial vision (or how well we see details and contrast) declines throughout the life span. Several reasons are responsible for this deterioration, ranging from the purely optical degradation to retinal and neural losses. In the aging eye, there are a higher light absorption by the ocular media, with different spectral contribution (what can affect the perceived color), a smaller pupil diameter (that is called senile miosis) and an increment of intraocular scattering.

We studied the problem of the eye’s optical properties (optical aberrations) as a function of age for the first time nearly 20 years ago. We showed that the ratio of contrast between the object and the retinal image, for a given spatial frequency, in a group of older subjects was lower than in a group of younger subjects. This result suggested that the ocular aberrations, besides intraocular scattering, increase with age. This indicates that the degradation in the quality of the retinal image in older eyes may play a role in limiting spatial vision. Different factors contribute to this increase in optical aberrations with age: possible modifications in the aberrations of the cornea, in the lens or their relative contributions. The corneal optical quality seems to be rather constant with age, but the aberrations of the crystalline lens changes due to the continuous modification of the lens shape with age. As the lens grows, its dimensions, curvatures and refractive index change, altering the lens aberrations. In addition, as the aberrations of the lens change with age, the compensation of aberration between cornea and lens (present in the young eye) is, partially, or completely lost. This may explain the overall increase in aberration and the reduction of retinal image quality throughout the life span.

The young eye is a paradigmatic example of an aplanatic optical system (http://pabloartal.blogspot.com/2008/09/eyes-aplanatic-answer-commentary.html). An aplanatic optical system forms images with minimal spherical aberration and coma. It is rather extraordinary to realize how the optical design of the young human eye resembles these characteristics, with the crystalline lens acting as an aspheric compensator providing a (partial) correction of corneal spherical aberration and avoiding major generation of off-axis coma. Because the angle κappa tends to be slightly larger for hyperopic eyes compared with myopic eyes, it is expected that a larger compensation effect exists for hyperopic subjects. This special design of the human eye is able to maintain constant optical quality independent of some alignment variables, thus making the design more robust and tolerant. So, the young eye approximates to an aplanatic optical system, only affected in general by small amounts of spherical aberration and coma. But… what happens to this mechanism with age? The eye becomes more aberrated on average. In particular, spherical aberration and coma tends to increase in older eyes. A factor to understand the age-related variation in the balance of horizontal coma might be angle kappa. For those of you that do not remember what is angle kappa in the eye, check this early post: http://pabloartal.blogspot.com/2008/08/on-definition-of-angle-kappa.html. Perhaps you would be surprised that this is the most visited post of this blog ever! So, the interest from readers to know about this ocular angle is quite curious!

Recently (http://www.journalofvision.org/content/10/14/34.full), Esther Berrio, Juan Tabernero and I, have just published a detailed and careful study on this topic: what are the reasons of the changes of the eye’s optics with eye in relation with the alignment properties. First, angle kappa seems to be stable with age (see picture below).

As a consequence, lateral coma remains compensated in most of the older eyes due to angle kappa remaining stable and the lens shape factor only experiencing small changes. Slight variations in the geometrical factors of the crystalline lens with age (radii and, perhaps, asphericity) produce modifications in its aberration structure that reduces the compensation mechanism, explaining most of the measured increment of ocular aberrations with age.

However… part of the aberration compensation is still present in older eyes with some older eyes behaving as a nearly aplanatic system. In addition, although the optics of the eye is moderately worst in older persons… the typical reduction in pupil diameter helps to keep a retinal image with a quality as good as in younger fellows. This is another nice compensatory effect. It is good to know that although things change with age (and usually for bad...) the balance is still good even at a late age… of course with cataract permission!

June meetings in Spain... do not miss the unique opportunity. Last days for a extended deadline for pre-registration and submission at:

The 8^th Adaptive Optics meeting in Murcia city... http://lo.um.es/events/aoim2011/AOIM2011.html.

The 3^rd Engineering the Eye meeting in Benasque (Pyrenees)... http://benasque.org/2011eye/

You can re-read some of my past post (nicely edited by Christina Folz) in the Optical Society of America "Bright Futures" blog... http://www.osa-opn.org/BrightFuturesBlog/post/Tips-for-Having-a-Successful-Career-in-Science.aspx

And finally a tribute to Japan and the Japanese people after the terrible earthquake and subsequent consequences. A special dedication to our Japanese optical and vision scientists colleagues, friends and blog readers. My best wishes to all of you and good luck! I took the picture below in my 2005 trip to Japan and I hope to visit the country again this summer!

Berrio, E., Tabernero, J., & Artal, P. (2010). Optical aberrations and alignment of the eye with age Journal of Vision, 10 (14), 34-34 DOI: 10.1167/10.14.34

How can I know if I have cataracts and its severity?

2011-02-07T16:58:00.011+01:00

Prof. Artal. Although, I am still in my late 50’s, I was having some visual disturbances, so I visited my doctor. After some visual inspection of my eye, he simply told me that I probably had some early cataracts. His recommendation was to wait until is more mature and then have surgery to implant an intraocular lens. It is hard to understand why with all the medical sophisticated technology available today, doctors cannot assess more precisely cataracts. This would help patients a lot. Any comment or advice? Anonymous. Portland, Oregon, USA.

This is one of those question that has been sitting on my desk for years… so my reader probably already had his cataract surgery done!, Sorry about that!

But, now is a perfect time for a revision of this extremely important, and typically not very much appreciated, problem. The reason is that I have just published on this topic an article in the open access journal: Public Library of Science One (PLoS One).
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0016823

We described a unique and objective optical approach to evaluate cataract. Antonio Benito, Guillermo Perez, Encarna Alcon, Alvaro de Casas, Jaume Pujol and Jose Maria Marin are the co-authors of this study. Those readers that prefer a simplified and shorter description, should keep reading this post... and those asking themselves the question: do I have cataract?... too.

Cataracts affect lens optics in ways that are not quantified by standard visual acuity measures. The most important is the induction of light scatter, which degrades the retinal image and places the patient in an increasingly foggy world. In addition, the developing cataract can produce a progressive yellowing of perceived light resulting from a discoloration and loss of transparency the crystalline lens. And although early signs of cataracts can degrade a patient’s visual experience, the same patient may score reasonably well on visual acuity tests performed under the bright conditions of an in-office testing room. Then, the chart acuity is an inadequate measure of the visual disability associated with developing cataracts. Cataracts that are less than fully mature vary in their optical effects and can degrade a patient’s visual experience in ways that standard tests fail to capture.

A usual complement to visual acuity testing is direct imaging of the lens at the slit lamp and subsequent grading. Unfortunately, direct imaging of cataracts has two major limitations. First, is subjective, and second, it failures to directly assess the forward light scatter that determines an eye’s retinal image. Instead, a slit lamp image of the lens represents backward light scatter reflected from the lens. However, forward and backward scatter do not correlate. In this scenario, objective measures of a patients’ visual disability due to cataract could be really important. We have proposed a more accurate assessment with a double-pass ophthalmoscope that directly records and analyzes reflected retinal images of a point source light. The concept is very simple (already mentioned in some previous post here). A low-power diode laser beam passes into the eye to produce a light spot on the retina; the reflected light then passes back through the eye to be captured by a digital camera. (See schematic picture below).

Computer analysis of the reflected light reveals the impact of lower and higher order aberrations, as well as a measurement of forward light scatter in the retinal image. Since the initial source is a point, a small and compact reflected image indicates good visual quality, while an extended, or blurred, point reveals degraded optics. From the double-pass images, the instrument’s software quantifies scatter to provide a numerical measure that we called the objective scatter index (OSI). An OSI score of 1 or less represents good vision quality; between 1 and 2 indicates early degradation that remains within the realm of “normal”; scores greater than 2 represent significant light scatter that can likely be improved with cataract removal; and values over 4 indicate severely compromised visual quality and an unambiguous indication for surgery. The value of these scores is greatest in situations where visual acuity and slit-lamp scores fail to account for a patient’s visual complaints. In these situations, a low OSI score can rule out cataracts as the underlying cause, while a high score can facilitate both a confident diagnosis and a clear explanation for the patient. The first situation is likely to correspond to my correspondent. See picture below with examples of slit-lamps and double-pass images in patients with different cataract severity.

In combination to standard tests of visual acuity and lens opacification, recording of double-pass images would represent an advance in the quantification of cataract diagnosis. I am quite happy to my personal contribution to this practical procedure. It is a nice example of an initially basic research that was actually initiated at the time of my PhD thesis supervised by Javier Santamaria (so, a long time ago...) in Madrid and that has been continued to the real world application as a clinical instrument (OQAS, Visiometrics) by Jaume Pujol and colleagues.

Note added. In January 2012, this study was reported in the Spanish National Television (TVE1). You can have a look of the video at: http://www.rtve.es/alacarta/videos/la-manana-de-la-1/saber-vivir-20-01-12/1299544/
(Go to minute 27. It is in spanish, but I am sure you would be able to follow and see the instrument under operation).

AND… DO NOT MISS the Adaptive Optics Workshop to be held in Murcia in June 2011. Abstract submission is NOW open (deadline February 28, 2011). http://lo.um.es/events/aoim2011/AOIM2011.html

What is happening in Spain?

Several international readers are asking me about the (difficult) economic situation we are having in Spain. Of course, my expertise is not Economy, but considering the “precision” of some of the economical predictions during the last years... I believe I could also talk about Economy… in an Optics blog! However, the topic probably deserves a full future post. For now, just have a look of the picture below that I took a few weeks ago. Dozens of unfinished (and aparently abandoned) houses in the Murcia region may represent well what is happening... But if you want to know my personal opinion on why we are here and what can happen next… please wait for the next post.

Artal, P., Benito, A., Pérez, G., Alcón, E., De Casas,, Pujol, J., & Marín, J. (2011). An Objective Scatter Index Based on Double-Pass Retinal Images of a Point Source to Classify Cataracts PLoS ONE, 6 (2) DOI: 10.1371/journal.pone.0016823

How a change of gaze affects the eye optics?

2010-12-28T10:16:00.008+01:00

Because of my profession I have a special interest in your posts dealing with the eye. In general, I find them too technical for my background and far from the clinical reality. I understand, however that your research will be important for the future. I know it is possible to measure the eye’s optics very carefully with aberrometers. In the case of refractive surgery, doctors can even drive the surgery from the eye’s measurements. My question to you, Dr. Artal, is the following: when you change gaze direction, the mechanical properties of the eye would change and then the optical properties. If this is true, the eye’s aberrations would strongly depend on the particular gaze direction. If this is not controlled, the eyes measurements will be simply be wrong. Am I correct? Optometrist. Bradford, UK.

I am happy to have professional optometrists, as you, from all around the world following my posts. I hope that at least some of them can be of potential interest even for the clinical practitioner. To be honest, I do not want to be too far from reality! However, my main interest is basic research and the development of instruments for the future. A friend told me once that this blog will probably have more readers in TEN years! In any case, your question is very relevant and a nice topic to be discussed in my last post of this year 2010!

During normal activities we change the direction of gaze all the time. You can look at an object in one direction with a fixed position of your head or you can try to look at the same object but when your head is turned. Teenagers and young people are remarkably good at looking with quite forced gaze directions (especially boys to girls and vice versa when they do not want to be noticed!). See the cartoon below (the first example here of my own drawing abilities), and imagine what he is looking at...

I was personally interested in this problem for a long time. How do eye optics (aberrations) change with gaze? In principle, it can be expected that the stresses exerted on the eyeball by the extraocular muscles, especially in extreme gaze positions, should affect ocular shape to a bigger or lesser extent, inducing somehow changes in the eye’s aberration pattern.

Around 10 years ago, I measured my own eye's aberrations with one of our wavefront sensors with a strongly forced gaze. The aberrations changed and I always assumed the effect could be somehow important. I prepared and used a slide for many of my courses and presentations during the last years (see below).

More recently, we took a detailed look at this problem. In fact trying to ask your question on how important this effect of gaze change could be in optical measurements of the eye. We measured aberrations in a group of subjects for different gaze directions using one of our fast Hartmann-Shack wavefront sensors. Our colleagues and friends from the University of Santiago de Compostela (Paula Prado, Justo Arines and Salva Bara) performed an in deep analysis of the statistical relevance of the results. In that study, published last year (Prado P, Arines J, Bará S, Manzanera S, Mira-Agudelo A, Artal P. Changes of ocular aberrations with gaze. Ophthal.Physiol.Opt. 2009 ;29:264-71;http://onlinelibrary.wiley.com/doi/10.1111/j.1475-1313.2009.00652.x/abstract), we took into account horizontal changes in gaze (as you know, we can do more complicated gaze changes). In abductions (horizontal eye movements toward temple) the lateral rectus muscle contracts and the medial rectus relaxes, while in adductions (horizontal eye movements towards nose) the medial rectus contracts and the lateral rectus relaxes. These extraocular muscles exert their action over the eyeball and it seems reasonable that if there is any distortion in the eye shape, it should produce some amount of astigmatism and coma-like aberration terms with axes oriented along the direction of the resulting stresses. We analyzed the changes in individual aberration terms, testing their statistical significance.

As expected, we found changes in aberrations with the change of gaze. However, this apperared to have little relevance, since the changes were smaller than the experimental variability. This is important from a practical point of view and, I believe answer your question: you should not be very worried if during the measurements the gaze direction is not properly controlled. Of course, that would add more error variability but it would not be very significant in most cases.

What is also quite interesting is that the eye appears to deal reasonably well with the different stresses produced by the orbit muscles when turning to a variety of gazes. Our eyes are mechanically prepared to keep a good retinal image even under strong tensions. You should know that if somebody is looking to you furtively… his retinal images would be still good!

In front of the White House… Juanma Bueno just passed this picture that somebody took us in 1998 when we were attending a conference of the Optical Society of America. At the time President Bill Clinton was still living there in his second term… It looks a little “prehistorical” now.

An hour of cross-country skiing after my March accident... I had the opportunity to practice a little of sky today in the mountains near Madrid. The place is a small and peaceful (except during weekends) miracle very near Madrid ( a mere 80 km).

Nice cross-county tracks with beautiful vistas to the Segovia valleys. Cross-country skiing is not very popular in Spain, and not too many people know there are nice places so close to the capital. This place is called "Puerto de Navafria" (http://navafriaesqui.com/). After my knee was injured in March, today was the first day I put on skis again… so I was excited and nervous. The temperature was great (not too cold) and the day sunny. The tracks are easy so I managed reasonably well. See the picture below of myself (well you need to believe it!).

And the LOUM 2010 greetings card for all of you. It is a recent group photo with the city of Murcia behind us and a collection of some of our experimental systems: our multiphoton microscope, the binocular adaptive optics visual simulator and the scanner peripheral wavefront sensor…

I take the opportunity of this last 2010 post to wish all the readers an excellent new year 2011.

Prado, P., Arines, J., Bará, S., Manzanera, S., Mira-Agudelo, A., & Artal, P. (2009). Changes of ocular aberrations with gaze Ophthalmic and Physiological Optics, 29 (3), 264-271 DOI: 10.1111/j.1475-1313.2009.00652.x

Optics & stereopsis: how 3D vision is affected by retinal image quality?

2010-12-12T23:02:00.009+01:00

Dear Pablo. I am a college professor enjoying your infrequent posts. I would be happy if you can discuss the problems of stereopsis after refractive surgery. I underwent surgery a few months ago and I had what is called monovision: one eye was set for good distance vision and the other for near vision. My visual acuity is acceptable both for near and distant objects, but… I clearly lost my 3D vision. I suppose the reason is the differences between my two eyes. How can be this tested in advance? Thanks, Andrew. Boca Raton, Florida, USA

Andrew’s case is very common and I am happy to elaborate on this problem. Human vision is a really remarkable process with many different features. As usually happens with other aspects in life, we only tend to value something when is already missing. This is what typically happens with stereopsis or depth perception (3D vision). Although we use this capability all the time, we are not usually aware. In reality, there are many people with poor stereo vision but they do not know about that. The recent popularization of 3D movies may change this situation since some people is often surprised not seeing 3D…

Stereopsis is the ability for discerning relative distances or separation in depth as a consequence of binocular disparities between the images formed on each retina. So, first obvious fact: we need the two eyes, where slightly different images of the scene are formed. The brain analyzes these differences extracting useful depth information. If one eye is forming bad quality images, this capability will obviously fail. However, as you can easily experience by covering one of your eyes, people with stereovision problems still can have some estimation of depth. Both experience and monocular clues might provide some information on depth. But, the exquisite fine details of 3D perception are obviously lost. Despite the general lack of recognition, the functional benefits of stereopsis in everyday tasks, in particular in certain motor skills, seem to be of importance.

It seems obvious that the image quality in each eye will affect the quality of the stereopsis. One simple, but important case is monovision. As Andrew clearly described this is a common practice in Ophthalmology to alleviate presbyopia. One eye is corrected for distance and the other is left slightly myopic, i.e.; having the near objects in good focus. Binocular summation and image suppression in the brain will work together to provide reasonable visual acuity for all distances without the need of spectacles. Some people are very happy with this simple solution. However, for a fixed range of distances, the image in one eye will be in focus, but not in the other eye… and then the sterovision system will not work properly. This is a typical trade-off for this solution of presbyopia.

In general, we do not know exactly the amount of relative blur that significantly impairs 3D vision. In this direction, we have recently developed a new instrument which can provide full experimental control of the eye's optical aberrations binocularly, while visual testing for obtaining stereo-features is accomplished. The system is a direct evolution of our binocular adaptive optics simulator (already reported in a previous post: http://pabloartal.blogspot.com/2009/08/binocular-adaptive-optics-simulator.html). You can find all the details of the instrument and some first experiments in a recent paper that Josua Fernandez, Pedro Prieto and myself published in the November issue of the Journal of the Optical Society of America A (http://lo.um.es/publications/PDFs_main/2010_JOSA_EJ_BinocularStereopsisFernandez.pdf). See below a schematic diagram of the instrument.

The binocular adaptive optics visual simulator can be used as a demonstrator to show the potential effect of a particular correction in a subject’s eyes. This use can be of particular interest in refractive surgery, where the instrument provides a method for non-invasively testing the potential outcome of the procedure before the subject actually undergoes surgery. Also in the case of intraocular lens implantation, the potential benefit of a lens incorporating high order aberration profiles or diffractive features could be tested in advance and in real time, to help in the decision-making process.

In the case of Andrew, he could had tried first the monovision condition and evaluate the benefits, but also the associated problems. For instance, the reduction in stereo acuity and perhaps deciding a smaller difference in refraction between the two eyes.

This figure shows an example of testing monovision in my own eyes with the AO simulator. One eye is well focus for distance targets, so has a good visual acuity (around 1 decimal, or 20/20), but visual acuity for near objects is very poor (around 0.2 for objects placed at 30 cm). These are the black symbols. The other eye was left myopic, so it has a good visual acuity for objects placed near, and bad for distance (red symbols). The binocular visual acuity (green symbols) nearly follows the best eye for each distance. Incidentally, my stereoacuity was reduced significantly.

The possibility of presenting stereo images in the instrument, producing true 3D perception of the scene, might open the door to an advanced method for finding the best binocular refractive correction based not only on spatial acuity. Stereopsis could be incorporated in the procedure, allowing subjects to perceive the impact of the eye’s optics in their 3D vision. This could be presented to presbyopic patients proposed to undergo a monovision-type treatment (such as the case of Andrew), so that the potential impairment in their three-dimensional perception could be assessed. Other potential application would be finding optimal solutions for subjects requiring special needs of stereopsis, as occurring for those involved in fine or precision manual tasks.

Meeting in the Pyrenees in June 2011. Together with David Williams and Chris Dainty, I am organizing the next Engineering the Eye III (EEIII) meeting. It will be held in Benasque, the spanish Pyrenees in June 2011! Do not miss this exceptional and unique scientific meeting. The program of invited talks is already available at the meeting we page: http://benasque.org/2011eye/

EEIII venue is the brand new and cozy Centre for Sciences of Benasque, directed by enthusiastic physics professor Jose Ignacio Latorre. Magnificent mountains nearby are a nature lover paradise. A combination of world-class science and pure fun that you should not miss! 15 March 2011. DEADLINE for pre-registration and abstract submission!

And a video... A few years ago, our laboratory was awarded with an excelence grant from the Murcia Regional government. Now, the regional agency for science has produced a nice video featuring us. Have a look at this link: http://www.f-seneca.org/seneca/html/GERM/video_germ.html#15_P

I prepared this post in Coimbra, the historical University town of Portugal. I was invited to give a lecture at the IBILI annual meeting. IBILI (http://www.aibili.pt) is a biomedical research institute of the University of Coimbra founded by Prof. Jose Cunha-Vaz. Rui Bernardes and Manuel Castelo-Branco, together with Prof. Cunha-Vaz, now officially retired, although still very energetic, were my hosts in Coimbra. I always enjoy visiting Portugal. So close, but so far from us in Spain, so similar and so different in many aspects. I specially like the old-time atmosphere. As a detail, have a look to the picture of a Coimbra paved sidewalk.

Fernández, E., Prieto, P., & Artal, P. (2010). Adaptive optics binocular visual simulator to study stereopsis in the presence of aberrations Journal of the Optical Society of America A, 27 (11) DOI: 10.1364/JOSAA.27.000A48

“Virtual cataract surgery”: advanced optics helping surgeons… and patients

2010-10-08T19:42:00.009+02:00

Hi Pablo, I am curious to know if the optical properties of the eye can be controlled before and after performing cataract surgery. Is possible to predict what may happen with the eye in optical terms? Angelo. Atlanta. USA

With normal ageing, crystalline lenses tend to become less transparent diffusing light and degrading the retinal image. In advanced stages of this situation, a condition called cataracts, the lens is nearly opaque leading to lower quality of vision. The standard, and successful, surgical procedure consists in the replacement of the cataractous natural lens with an artificial implant, called intraocular lens (IOL) that restore the eye’s ability to form clear images on the retina.

Cataract surgery is probably one of the most widely practiced surgical procedures worldwide and clearly the most directly affected by optics! As the readers of this blog already know, the optical properties of the eye are already well understood (for new readers see first, for instance the previous post: http://pabloartal.blogspot.com/2009/01/easy-description-of-eye-cross-country.html). The implanted IOL during surgery will couple optically with the patients’ cornea. Depending on different parameters, IOL centration after surgery and positioning will result the final eye’s image quality... and the quality of vision of the patient.

Based in this ideas, we developed a few years ago a computational procedure to actually predict the optics of the eyes after cataract surgery within different possible situation. In a sense, this would be like performing multiple possible real surgeries, but in the computer! We called this approach “Cataract virtual surgery”. This idea was published in 2006 in the scientific journal IOVS by Juan Tabernero, Patricia Piers, Antonio Benito, Manuel Redondo and myself (http://lo.um.es/publications/PDFs_main/2006_IOVS_juan.pdf).

It is based in a customized and realistic modeling of the pseudophakic eye's optics. To build up our customized computational model we need to know the cornea, which is approximated by a one surface model constructed using real data derived from corneal topography, the specific IOL design and also how tilted and decentrated the IOL was after surgery together with other ocular biometric data. The customized modeling produced data of the eye’s aberrations and retinal images. See figure as a schematic description of the procedure.

What was nice with this approach is that when compared the aberrations predicted by the modeling with those actually measured after the REAL surgery were extremely well correlated. This was considered a validation of our procedure that permitted its application to study any type of IOL design and different structural configurations. In others words, we were able to perform a customized “virtual surgery” for each particular cataract patient.

Using this modeling we were able, for instance to compare lenses or to study the maximum IOL decentration that could be acceptable. For design purposes this is a extremely useful tool that other groups, both academic and industrial, have followed. For the particular case of aspheric IOLs (se previous post: http://pabloartal.blogspot.com/2009/01/aspheric-intraocular-lenses-mimicking.html), we demonstrated by using this procedure that the tolerances were large enough to provide an optical benefit from an aspheric design IOL within the limits imposed by modern cataract surgery.

In the near future, we can speculate that with even improved surgical techniques, it will be possible to incorporate all patients data and performed many virtual surgery procedures until the optimum optical choice is achieved. Then, the real surgery will be actually performed. Surgeons and patients will be relieved to know that at least optically everything will be perfect!

This blog re-printed in OPN, the magazine of the Optical Society of America. I was happy having some of my previous posts dealing with research careers issues reprinted in the new OPN blog: Bright Futures. I hope this will be of help to OPN readers! http://www.osa-opn.org/BrightFuturesBlog/

I was interviewed for “La Verdad”, the leading Murcia newspaper. Last Sunday, a long interview was published, covering some aspects of our research activities, research policy in Spain and the situation of our university ... I have to tell you that not everybody seems to be happy with my opinions... If you want to have a look, here is a direct link (in Spanish): http://www.laverdad.es/murcia/v/20101003/region/ciencia-politica-encajan-20101003.html

Picture of Pablo Artal in the lab taken to ilustrate the interview published in "La Verdad" newspaper.

Juan Tabernero’s wedding! Juan (the first author of the article featured in this post) get married last Sunday in the center of the city of Murcia with his longtime girlfriend, Estela. See group picture with lab members and families. I wish Juan and Estela the best for the future and good luck!

Tabernero, J. et al. (2006). Predicting the Optical Performance of Eyes Implanted with IOLs to Correct Spherical Aberration Investigative Ophthalmology & Visual Science, 47 (10), 4651-4658 DOI: 10.1167/iovs.06-0444

Seeing double? Perhaps is simply optical diplopia

2010-08-31T19:41:00.009+02:00

Prof. Artal. My mother is recently complaining of seeing double images. I know this condition is called diplopia. I checked the internet and I was terrified since this can be produced by many very severe illness. I am a physics student myself and I have the impression that this could be also due to the eye. Do you have some experience on this topic? Ernesto. Cordoba. Argentina.

Ernesto, you are completely right. Diplopia can be produced by the eye when affected by severe optical aberration or scatter. Your question is also timely, because we recently studied in detail one patient complaining of diplopia. I believe this can be illustrative as an example. One typical situation that tends to produce diplopia is the development of cataract. The sclerosis of the crystalline lens imposes changes in the eye’s optics that, in some cases, can even induce monocular polyopia (as refereed to seeing multiple images, when diplopia indicates the perception of two images).

The best way to determine if a condition of diplopia is due to the eye's optics is to directly measure the retinal image of a point source. This can be done directly by recording the double-pass retinal image, projecting a point source into the retina and recording the light after reflection and passing two times through the eye, or indirectly by measuring the optical aberrations using, for example, a Hartmann-Shack type wavefront sensor (http://lo.um.es/publications/PDFs_main/josa_HS_ago00.pdf).

As an example, I will show to you here images obtained in a real patient (a case that we recently published in the Journal of Refractive Surgery:

http://lo.um.es/publications/PDFs_main/2010_JRS_Cause%20of%20monocular%20diplopia_GM%20Perez.pdf

A patient complaining about monocular diplopia in both eyes was referred to the Ophthalmology service of the "Virgen de la Arrixaca Hospital" in Murcia. Our clinical collaborator, and co-author of this paper, Jose Maria Marin is the medical director. Other co-authors were Salome Abenza and Alvaro de Casas, at the time residents in the hospital and Guillermo Perez, then a PhD student in my lab. The patient complained about a secondary image which appeared displaced mainly vertically but also slightly horizontally from the primary image. What was peculiar, although also a common phenomena, was that the double image was only visible when the conditions of luminance were low.

We used our own wavefront sensor to measure the eye's aberrations for pupil diameters of 3 and 6 mm (this would corresponds approximately to conditions of bright and dim light). From the optical aberrations, we calculated the simulated retinal images of a point source and an object test. See the figures below. The image of a point for a small pupil diameter (3 mm) and for a large pupil diameter (6 mm). In this case, for the larger pupil, the image of a point source in the retina has two clearly separated maximum that could produce the pupil dependent diplopia.

The best way to see the effect is to calculate the retinal image of a letter chart as described in a previous post (http://pabloartal.blogspot.com/2008/10/to-be-cited-or-not-to-be-cited.html). This is actually done by computing the convolution of the image of a point (above) and the perfect letters image. The images below nicely shows the duplication of the letters and then the diplopia for the large pupil (note that the image in the retina for the smaller 3-mm pupil is not duplicated).

This exploration nicely showed the optical origin of the problem. The direct visualization of these images does resolve the diagnosis because it makes evident that the vertical diplopia responds to the changes on the aberrations pattern due to the existence of an optically inhomogeneous area. The dependence of the double vision with the pupil diameter is also explained. The diplopia becomes evident only for the pupil diameter of 6 mm since the responsible inhomogeneous area is localized in the upper part of the crystalline lens which is not affecting vision when the pupil diameter is smaller. In this patient, cataract surgery was programmed and successfully performed. Diplopia disappeared completely in the exam one week after surgery.

This case nicely reveals that modern optical analysis methods are quite useful to first identify potential optical problems in the eye. And you can see that in many cases... double vision can be easily explained by optical concepts.
However, for most people double vision is often associate with too much alcohol... and of course our optical tools cannot help for that conditions!!!

European Visual Optics meeting in Stockholm. I attended last week this nice and interesting meeting (http://www.myeos.org/events/stockholm), in this occasion organized by Linda Lundstrom (a former post-doc in my lab) and Peter Unsbo from the Royal Institute of Technology (KTH) in Stockholm, Sweden. Klaus Biderman, the retired Optics Professor at KTH was also there and organized a nice photo group that I hope I can link from here when is available. The meeting was lively, full of interesting lectures and old friends. I discussed about the issue of night myopia (as some of you asked about this, I promise to treat this topic in a complete future post). The next meeting in this series will be in Dublin, organized by Brian Vohnsen, another former post-doc here in Murcia. See picture below of a grey August day in Stockholm. As an anecdote the same day in the morning in Stockholm we had around 15 degrees Celsius and late at night when arrived home in Murcia (in one of the most hot days in the summer) was 38 degrees... hopefully the summer is nearly over!

Catalina. Some readers asked me for an updated photo of my cat. So, here you have one recent picture... and going back to the eyes, look at the elongated pupil. In a future post I will dedicate some space to talk about the different shapes of the eye’s pupil in different species. By the way, other discussion topic in the Stockholm meeting was the optics of the eye in the periphery... and in that conditions, when we look eccetric objects, our pupils are actually elliptical!

Some of these posts are linked at Research Blogging http://www.researchblogging.org/, a collection of blog posts based in peer reviewed research. It was nice to be one of the finalists in the 2010 awards (category best expert-level science blog).

Pérez, G., Abenza, S., De Casas, A., Marín, J., & Artal, P. (2010). Cause of Monocular Diplopia Diagnosed by Combining Double-pass Retinal Image Assessment and Hartmann-Shack Aberrometry Journal of Refractive Surgery, 26 (4), 301-304 DOI: 10.3928/1081597X-20100218-05

Frequency of posts, comments... and Omi

2010-08-06T17:36:00.006+02:00

I like your posts, but I have a question: why are you writing less and less? Last year you published two posts per month. And now this is less than one. Please, write more. Anonymous comment.

My anonymous correspondent is certainly right. In this year, the frequency of posts is around one per month. Two main reasons:

a) I like to have new and different full histories for each post... and this takes time.

b) I need some time to prepare each post… and often I cannot find it!
In any case, I will try my best to keep (at least) the current frequency. Some good news: I added two new utilities to the blog. A search bottom that will allow readers to explore within the posts for specific details; and labels for each post in different categories.

With this one, there are already on-line 44 different posts. It is not bad even considering the slow writing! So, I think labels will help new and frequent readers to select what they want to see.

Comments. I always encouraged readers to leave comments on each post. That is the reason that I keep that option always open and anonymous. However, in the last months I have been receiving more and more comments that tried to promote some products or services, both directly and indirectly. Curiously in some cases, completely non-scientific products, what it is a paradox for a science blog! I had to spend some time going through those comments to delete them.
So… I decided to incorporate a moderation of the comments. This would change very little to the readers wishing to post normal (non commercial) comments. The only difference will be that the comments will not appear immediately, but after a few hours. I tried to avoid this decision, but I believe is the right one. I hope this DO NOT prevent any of you to leave more comments in the future. In fact, the beauty of blogs is the communication using comments.

And finally, OMI. Some of you ask me often about my dog Omi, mentioned in some previous posts. I wanted to share with you a short video clip of Omi running near my house a few days ago.

How a changing world affects senior scientists?... and summertime pastimes

2010-07-30T20:27:00.004+02:00

Prof. Artal, I guess my situation is very different from most of your typical readers. I am an university professor near the retirement age. But, to be honest I feel confused on how other scientists (of course, younger than me) behave these days. I should not say that many actions look to me unethical… but not too far. Do you have the same experience? C.A.S. Poland.

Dear C.A.S., I am still relatively far from my retirement age, but I fully understand what you said to me (Note to readers: C.A.S. sent to me a longer letter with more specific details). It is obvious that as the world is changing in so many aspects, science and scientists are also continuously evolving.

Prof. S. mentioned that he cannot recognize any more the collegiate atmosphere and now competition is the norm. I have to say that this can depend on different fields. In my own, Optics, I think many people still highly values long time friendship with colleages. It is true that competitions and pressure for funding and permanent positions are always there. But in my experience, young scientists should look more with long-term perspective. Good relationships (friends) are better than short-term apparent victories that produce angry future potential enemies!

In what I fully agree with S. is in the changing approach to publications. In the old days, people wanted to have solid papers, typically very long and serious ones, reporting quite meditated and validated results. Papers that should last very long and that eventually would become classic references in the field. I still have personally that ambition permanently… but the common tendency, unfortunately is to have a lot of short papers, produced quickly. In some cases, some people are not worry if eventually the data reported were even wrong! What can you do as a senior scientist? Well, little, or a lot! You should try to keep your original (high) standards. I do not believe you should try to adapt some bad habits to your final career years! In any case, you should balance your students ambitions to publish very, very quickly. After all, they will be grateful if you stop some weak paper that could be rejected, or even worst, published with some defaults.

Something that is really changing fast and adaptation can be tough is the different way on how science is communicated. Some young scientist are really very good in using alternative channels to publicize their results beyond traditional approaches. Blogs, social networks, connections to science journalists. I believe this is OK, and well, you should try to emulate then or if not, not to complain.

You also mention than in some cases you can see some unethical behavior in younger colleagues… well, again in my personal experience, unethical or inappropriate behavior is more or less equally distributed among scientists of any age. And perhaps even more in the older cohort! Fair play in this game of science is fundamental.

And one final comment. It is obvious that as we get older our roles in science change and we need to know how to adapt, both to survive and to do even better. Your experience is increasing with time and you need to use that experience in combination with a reasonable flexibility to adapt the new situations. An exposure to younger colleagues is a good way to keep you younger (at least in mind!). I like to be challenged by younger colleages!

Summertime. We are navigating through the deep summer. As you know, this period of the year is specially hot here in Murcia, but of course, not only here… I was recently in Helsinki, giving an invited talk at the Euro-American workshop in Information Optics. I was curious to visit Helsinki in the summer. I was there in February this year and the experience of cold weather was a impressive shock. Well… Helsinki in mid July with temperature around 35 degrees Celsius… was also a shock! With no air condition in most places (including the conference room), you can imagine. In any case, it was nice to compare. The same city looks so different... See pictures of the same spot in Helsinki in February and July! (I suppose, no big problems to distinguish!).

In early July, I was also lecturing in the Aegean Summer School in Visual Optics, held near Heraklio in Crete, Greece. This year I went with my children and, instead of flying from Athens, we took three ferries with day stops in the islands of Milos and Santorini. I really enjoyed and I would recommend specially Milos (see picture).

A summer reading recommendation. Unfortunately, I have not time to read novels often, so my recent personal experience is limited. But, I just read, and I am really liked, “Summertime” by JM Coetzee. (The title is really good for this time of the year!). I was a reader of Coetzee before he won the Nobel prize in 2003 and after the prize he is still doing very,very well. This is a semi-fiction biography, interesting and also very tough at some points. I can often indentify with the main character (Coetzee himself). After all, we, scientists are probably not so different than writers! I read the Spanish translation of the book (“Verano”). Highly recommended reading!

Partridges and coral fossils… just a few meters from my office!

As some of you already know, our laboratory is at the edge of the Campus overlooking the city of Murcia at the distance without other buildings on one side. From time to time, I can see “happy” partridges less than 3 meters from my office window (see picture). But this area was clearly covered by the ocean millions of years ago. Josua Fernandez discovered many nice well preserved coral fossils just a few meters from our windows (see one below). It is nice to see the partridges walking around the fossils…

A recent paper. A few months ago, a nice paper reporting 2-photon microscopy images of ocular tissues was published in the Journal of Biomedical Optics. I already mentioned this work with Juanma Bueno and Emilio Gualda as co-authors in a previous post (http://pabloartal.blogspot.com/2009/05/ultrafast-lasers-to-see-and-treat-eye.html). Now the complete paper is available: http://lo.um.es/publications/PDFs_main/2010_JBO_2photonRetina.pdf

Gualda, E., Bueno, J., & Artal, P. (2010). Wavefront optimized nonlinear microscopy of ex vivo human retinas Journal of Biomedical Optics, 15 (2) DOI: 10.1117/1.3369001

The exploration of the eye as an optical instrument: the latest 400 years

2010-06-30T15:57:00.003+02:00

I found fascinating how the eye operates as a simple optical instrument. I am not a scientist by I am curious to know how the main discoveries on the eye occurred. Marcelo. Tel Aviv, Israel.

As I have discussed often in these posts, the human eye is a paradigmatic example of a very SIMPLE optical instrument providing EXCEPTIONAL functionality. I personally like very much how these two words combine in nature, and in the particular case of the eye. The eye as an optical instrument is simple and robust but provides the required capabilities. This is a lesson of practical engineering!

Although the interest for the eye is intrinsic to human nature, it is around Galileo’s time when the scientific exploration of the eye began. Then, there was already a basic understanding of some of the refractive errors of the human eye. It was evident that a normal emmetropic (perfectly in focus for objects at infinite) eye was most comfortable viewing light originating from a far distance. This observation was one of the reasons why the Galilean telescope worked adequately when a secondary negative lens was placed in combination with a large focal length positive lens. In the case of the telescope, the impact of Galileo´s discoveries, generated a “telescope race” improving quickly the optical quality of the instrument; increasing the field of view with Kepler´s eyepiece design, suppressing chromatic effects with Newton´s reflective designs, minimizing aberrations with the adequate surface shape calculated after Snell´s law, etc….

But in the case of the human eye, the understanding and correction of the ocular aberrations followed a slower evolution. Previously to Galileo´s times, spectacles for the correction of presbyopia and myopia were already known and sold by Italian glassmakers in Florence based on empirical testing, until Kepler correctly described how spherical lenses correct myopic and hyperopic refractive errors. However, it took a long way to characterize and correct astigmatism. At the beginning of the 19th century, Thomas Young correctly described the astigmatism of his left eye and it took almost 30 years to find the appropriate astigmatic correction. It was Airy in 1827, who suggested the use of cylindrical shaped surfaces to compensate for refractive errors along certain meridians, a spectacle design that is still very common today.

The ocular spherical and chromatic aberration were both well known due to the limitation they imposed to telescopes and microscopes. The first observation of spherical aberration in the human eye seems to be made (again!) by Thomas Young in his famous 1801 publication “On the mechanism of the eye” and later by Helmholtz in his “Treatise on Physiological Optics” in 1855. The chromatic effects in the eye were initially mentioned by Newton and later by Young. However, the correction of chromatic aberration by using achromatizing lenses was only tried in the mid of the 20th century and some variations of corrector providing wide-angle performance were proposed even recently. We worked together on this with Erez Ribak, and her student Yael Benny, from Technion in Haifa several years ago. If some of you are more interesting in this topic, you can read our 2007 article: Y. Benny, S. Manzanera, P. M. Prieto, E. N. Ribak,P. Artal, J. Opt. Soc. Am. A, 24, 1538-1544 (2007). "Wide-angle chromatic aberration corrector for the human eye".

http://lo.um.es/publications/PDFs_main/2007_JOSAA%20Chromatic%20corrector.pdf

Continuing with a simplified historical revision, Kepler, Scheiner and Descartes, contributed to the initial understanding of the eye as an optical instrument realizing that the image on the retina was inverted and providing the first description of the optical components. Later, Huygens built a physical eye model made of two hemispheres filled with water and a diaphragm. But, it was only at the beginning of the 19^th century when Thomas Young produced the first geometrical optics description of the cornea and the lens. The radii of curvature of corneal and lens surfaces, as well as the anterior chamber depth and the refractive index values were strikingly well estimated for those times. Later, Moser (1844) and Listing (1851) built schematic eyes using spherical surfaces to describe the cornea and lens. The Listing eye model was improved by Helmholtz modifying the positions of the lens surfaces. Those schematic eyes were three surface models, one for the cornea and two for the crystalline lens. The radius of curvature of the posterior corneal surface was measured for the first time by Tscherning, and he described the first four-surfaces schematic eye model in 1900. After that, based on the improvement of the techniques for measuring the eye curvatures and axial distances, several eye models were proposed in the last century, and some of them became very popular like the Gullstrand, Le Grand and Emsley eye models. The use of these spherical models should be restricted to the paraxial geometrical optics.

However, these simple models could not be used to fully understand the aberrations of each component. Since the surfaces used were rotationally symmetrical spheres, ray tracing through the schematic eyes would immediately show that the predicted values did not agree with the measurements. The accuracy of the models was restricted to the paraxial optics. After nearly 350 years, the actual aberrations of the cornea and the lens were largely unknown until our recent studies we performed to better understand the eye as an aplanatic eye (see previous post: http://pabloartal.blogspot.com/2008/09/eyes-aplanatic-answer-commentary.html).

This has been an exciting history leading us to a situation where we know “nearly” everything on the eye’s optics. And the best is that we, and others, are using this information to develop better lenses mimicking the eye. http://pabloartal.blogspot.com/2009/01/aspheric-intraocular-lenses-mimicking.html

Juan Tabernero and I put together review paper recently published in the journal “Applied Optics” in a special issue celebrating on the 400 years from Galileo’s time. You can have additional information on the history of visual optics in this article.

http://lo.um.es/publications/PDFs_main/2010_AO_galileo_eye_history_Artal.pdf

As you can easily see from the dates of my last post, again I am slow in keeping my writings… Again as some excuses, the last weeks were quite busy and I had some extra travel. I was in Berlin and I visited the Pergamon Museum. My second visit after more than 25! In that visit to Berlin (still with the wall), everything was so different… (except for the masterpieces at the Pergamon! see picture…).

Some of you asked privately about my knee accident. Yes, I had a sky accident in March and I damage my knee… so my sky days seem to be clearly over! Perhaps I can do some cross-country skiing… not sure. (http://pabloartal.blogspot.com/2009/01/easy-description-of-eye-cross-country.html)

That was the reason I had to cancel several trips and I was even more behind schedule in everything. So far I had physical therapy and avoided surgery, but I am not sure what will happens finally (I cross my fingers…).

I am in my way to the Visual Optics Summer School in Crete (http://www.ivo.gr/en/education-conference/summerschool/summer-school.html). This is a traditional gathering of visual optics researchers and students in a fantastic location. I always enjoy visiting Greece. I hope this year strikes are not affecting us too much! (See my picture walking within a Cretan gorge a few years ago during one of the previous Summer schools).

Artal, P., & Tabernero, J. (2010). Optics of human eye: 400 years of exploration from Galileo’s time Applied Optics, 49 (16) DOI: 10.1364/AO.49.00D123

Why kappa angle is larger in hyperopic eyes?

2010-05-05T16:45:00.003+02:00

HelloPablo. I have to confess that I am more and more confused about the concepts ofangles in the human eye. I know that the kappa angle is larger in hyperopes ascompared to myopes, but I do not understand what the reason is for this. Isthere any simple explanation? An anonymous ophthalmologist in residence. London, UK.

Thesedays I am receiving more anonymous questions (well, in fact persons asking meto be maintained as anonymous). Honestly, I do not understand the reason. Inthe case of this particular question, most ophthalmologists and many visualscientists have problems understanding the quite confuse terminology on ocularangles. So, it should be normal to ask openly!

I recognizeone important problem in science (and in life in general): to pretend we knoweverything… big mistake! Once you recognize you do not know something you arein the good path to understand it. In any case, coming back to kappa angle andthis question...

In one ofmy first posts (and still one of the most popular since many people search theweb for accurate descriptions of the kappa angle), I discussed the definitionsand differences between angles kappa and lambda (http://pabloartal.blogspot.com/2008/08/on-definition-of-angle-kappa.html):The angle kappa is the angular distance between the lineof sight and the pupillary axis.

And yes, hyperopiceyes tend to have a larger angle kappa than myopic eyes. It is relatively easyto understand the reason for this tendency (keep in mind that large individualvariability may occur). This can be explained by a simple model of axialgrowing of the eye. It is well known that one of the mechanisms for thedevelopment of myopia is an abnormal axial grow of the eye. Therefore, it isexpected that the fovea would remain relatively unchanged in its position withlittle migration in this direction, since the main growing of the eye is axial.Assuming that the foveal position is stable in the growing eye (see figurebelow) and also that the change in the approximate nodal points of the eye issmall in comparison to the change in the axial position of the retina, it canbe deduced a simple model of how angle kappa might change with the axial lengthof the eye.

By direct inspectionof this figure, you can see that the angle in the longer (myopic in blue) eyeis SMALLER than in the shorter (hyperopic in red) eye.

Of course, thevariation among subjects can be large and probably there are importantindividual differences that cannot be predicted with this model. However,simple geometry explains (at least partially) the influence of eye elongationon the values of angle kappa.

And this hasimportant implications for the eye’s optics. See for instance for moreinformation: http://www.opticsinfobase.org/abstract.cfm?URI=josaa-24-10-3274

EarlyMay… and unexpected cold weather. Iusually mention here the weather, for good or bad. In Murcia, warm weather iscommon since late March and of course, in May can be real, real summer withtemperatures well over 30 degrees Celsius. Well… after an unusually long andcold winter, we have this week temperatures that are more common in February…and for the first time since I am living in Murcia (already 16 years…) I usedthe heating in my house in May. Random fluctuations on the tendency of global warming? like a hyperope with small kappaangle? In any case, I confess I like this fresh weather!

And havea closer look of my lemon tree blossom (I hope I will have some lemons thisyear)…

Why should I pay taxes to fund (basic) science?

2010-04-30T20:23:00.004+02:00

I believe I pay too much money in taxes. Some of that money I suppose is used to pay your salary and your equipment; and the salaries, trips, assistants, of many other scientists and professors. Please, give me one single reason why this can be good for me (a normal citizen). I would prefer that ophthalmic companies (in your particular research area) do all the science privately and simply charge the costs to the final consumer. AA.

This is a “classical” question. Why taxes should pay some activities that may appear as "superfluous"… Why not leave all the research and developent activities to the private enterprises? This would surely save money (although I am not convinced that your taxes would be reduced in any case!!!). In an extreme position, why suporting any research at all??? Of course, my views on this are quite biased. I could give you many reasons. For instance, you seem to be reading my blog... well, many of what is described here is the result of my (mostly) government funded research.

But I think it can be more effective to describe here a practical and real example from my own research. Basic results obtained for the pure pleasure of understanding how the eye works that had significant impact in the development of solutions and products already in use. I do not believe that we would be in this situation in a scenario where all the research were performed without public funding. You must know that in every case, industrial research uses massively government funded basic research. So, perhaps your (our) money could be better distributed, but it is really necesary to promote science to offer people a better life. And, keep in mind that every good new applications you like to have are always based in previous good basic science.

A practical example: from the understanding of the eye´s optics to better ophthalmic corrections...

The fact that corneal and crystalline lens optical aberrations are partially balanced (a topic already covered in one of my first posts: http://pabloartal.blogspot.com/2008/08/eye-as-optimized-aplanatic-optical.html) generated research about the hypothetical situation where this fine tuning might be disrupted. And this happened only because we gained that basic understanding first! The eye is a very simple instrument (see picture below compared with an objective lens).

Certainly, some modification of either the cornea or the lens can occur in ophthalmic surgery situations, like refractive or cataract surgery. Standard refractive surgery procedures can disrupt the aberration compensation, especially in hyperopic corrections leading to the idea that improved ablation profiles, inducing less aberration may be required.

Cataracts are opacifications of the crystalline lens that typically occur with age. The common current solution is to replace the opaque lens by an artificial intraocular lens. The first experimental works on the in-vivo optical quality of eyes implanted with intraocular lenses showed an apparent paradox. The retinal image quality appeared to be similar to that of normal patients of the same age. Intraocular lenses are manufactured with high optical quality standards, better than isolated older human lenses. However when implanted into the eye, the resulting optical quality was not significantly improved. The compensation of aberrations in the normal eye provided an explanation to this paradox, and more interestingly, a potential solution. The best intraocular lens is not diffraction-limited, but a lens with opposite aberrations to that of the cornea, mimicking the situation in the young crystalline lens. This actually opened a new era for the optical design of intraocular lenses (http://pabloartal.blogspot.com/2009/01/aspheric-intraocular-lenses-mimicking.html)

And the most important, the current better understanding of the eye’s optics will surely contribute to new potential practical applications. Virtually, every future idea for visual correction will need to consider carefully the optical properties of the eye. Combining new materials and surgical technologies with optics have the potential for improvements in every approach. In the study of the human eye, there is a convergence of optical physics and photonics together with materials, instrumentation and surgery. Ideally, a combination of all these disciplines will make possible to provide patients with a better assessment, evaluation and correction in the future.

This will be much better for the patients… and eventually you will need a cataract surgery. If the lenses based in our basic science provide you a good vision… I am sure you will think that the cost (your taxes) were a really good investment.

Accidents… In the last weeks, we suffered in the lab several accidents. Pedro Prieto was very unlucky and when exploring around our building (still under permanent construction works that seems to be never ending) seriously damaged his back and hand. He had surgery and will need some time to fully recover. I wish Pedro the best and a quick and complete recovery (I will share with him privately a picture I took when the paramedics rescued him). And I suffered a ski accident a month ago. I severely damaged my knee and I am recovering very slowly… too bad!

As some readers may remember, I like cross-country skiing (http://pabloartal.blogspot.com/2009/01/easy-description-of-eye-cross-country.html)... but I made the mistake of joining my children one day doing downhill ski in the Aragon Pyrenees… my poor ski technical abilities and my attempts to follow them… caused the disaster. I may also need (not sure yet) surgery and I had to cancel my trip to the ARVO meeting in Florida (http://pabloartal.blogspot.com/2009/01/arvo-fellow-unexpected-award-and-real.html) and I also cancelled a couple of other business trips. Just life…

Panoramic pictures… I always liked panoramic pictures and I used to compose myself with not very good results. You may know that in same new compact cameras there are some powerful tools to take really good panoramic pictures in a very, very, simple way (as easy as moving the camera around). See below an example of a more than 160 degrees view picture I just took from my kitchen window!

And a recommended movie… this is my first movie recommendation here! A relatively long movie in German and in black and white… perhaps this sounds difficult, but you should try. “The white ribbon” directed by Michael Heneke is the type of movie that grows more and more the days after you watch it. A history from the early XX century in rural north Germany, but in fact as universal as human behavior. I particularly liked the multiple options you have to interpret what actually happened…

Tabernero, J., Benito, A., Alcón, E., & Artal, P. (2007). Mechanism of compensation of aberrations in the human eye Journal of the Optical Society of America A, 24 (10) DOI: 10.1364/JOSAA.24.003274