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.pdfA 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!!!
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
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4 comentarios:
Pablo, this is really interesting. I am confused however. In my mind, diplopia is a binocular phenomena. Each eye have different images and then the brain fail to combine them. But you are talking here as I understand only on one eye. Is this correct? Thank you. B.
This is a very good point. Thank you B. You are right, I forget to mention clearly that in many cases, diplopia is a BINOCULAR effect. However, it may also occur in only one eye, what is referred as monocular diplopia. This is the case I detailed in this post with a pure optical origin.
Hi there, was searching for diplopia and found your item. I'm from the other end of the line. Now 53 yrs, I (mail) first noticed the effect when driving in a tunnel in Austria, about 15 yrs ago. The red lights alongside the road were double at far distance (300 mtrs) and turned out to be single at 20 meters. With both eyes I have a second image above the normal image, left eye counter clockwise – right eye clockwise (I think – or just opposite, might check tonight ;-), both about 10 degrees. The more dark, the more effect. The more white the color of the light the less hinder of the effect, blue lights (black lights) are extreme.
By now I notice some effect during daylight but not too much. The image ‘feels’ not fully steady. When concentrating on the image it ‘feels’ steady. According to diagnoses at the local hospital the lens is clear – that’s what I’ve been told. We will see (!) for the coming years.
I can control if I see one or two images. I've been able to sence birth. I can control it to the point where I can pull the two images apart so hat there is no fuzzyness. Should I be concerned?
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