Here is a very simplistic overview of some vision stuff, a bit of background.
Light from the world enters our eyes, goes through the lens, and is projected on the back of the eyeball, the retina. The image is converted to a form that the optic nerve transfers to the brain and the brain actually does the processing (kind of strange to realize that it is really the brain that does the seeing in some ways).
Most people who have “typical” vision issues have problems with the eyeball part. Often the issue is optical, something in the image -> lens -> retina pathway resulting in an out of focus image on the retina. For many of these issues there are corrective measures, most commonly glasses or contact lenses. Hence an optical solution to an optical problem.
Others have issues with the optic nerve. The nerve may not conduct the image as it should for a whole host of reasons. Cortical visual impairment (CVI) is when there is a neurological reason for the vision problem, an issue with the optic nerve or the brain itself. Again, this is a simplistic explanation, but works for now.
There are ways to evaluate the optical system. The easiest is a common eye chart, something we are all familiar with. Almost as easy is to project an image into the eye, and look (from the outside) at the retina and see how well the image is projected onto it. Cool, no? This is how to tell how well an infant can optically see.
Testing the optic nerve and brain is just slightly more complex. Electrodes can be attached to the head (as in an EEG, but fewer) that will pick up electrical activity in the parts of the brain that are involved with vision. If you have a computer monitor flash back and forth from all black to all white, your brain will react when you are looking at it. Those electrodes will respond in a synchronized way to the flashing screen, to a point. If the screen flashes to quickly all you will see is gray, and the brain electrical pattern will stay steady. There is a common flash rate that is known where you should stop seeing black / white and you see gray. Also, instead of using the entire screen to be all black or all white, how about a black and white checker board pattern where the black squares go white and the white squares go black? We can vary the size of the squares (too small and it is all gray) and the flash rate, while watching your brain. Doing all this allows one to understand the working of the optic nerves and other gray matter. This is the simplistic basis of a visual evoked potential (VEP) as explained to me, and demonstrated on my kids, by the inventor of the now mainstream technique.
Modern medicine can determine a number for your vision, optically and neurologically. That number can be the same or different. If you have completely “normal” (don’t you hate that word?) vision, so called 20/20, then your optical vision is 20/20 and your neurological vision is 20/20. (Don’t go asking your doctor about the term “neurological vision,” I think I made up the term, but not the concept.)
One other concept … limiting factor. The “limiting factor” is the item that controls a process or decision. Let’s say you are a family of five and want to buy a small, eco-friendly car. The limiting factor is that it must seat five. It can seat more, but not less. It can only be as small and eco-friendly as a five seat car, you are limited by the number of seats.
Both of my children have been evaluated by the best ophthalmology team around.
Pearlsky’s neurological vision is 20/225. Her optical vision is 20/270. The limiting factor to her vision is her neurological vision, her optic nerve limits how well she will see. If we fix her optical vision, which we can greatly improve with glasses / contacts, even if we get it to 20/20, she will still only have 20/225 vision because that is the best her optic nerve can do. There is no known way to fix the optic nerve. The question for Pearlsky is is it worth the minor improvement in vision to deal with glasses? The best we could do is go from 20/270 to 20/225. Never better, a very minor improvement.
David’s neurological vision is 20/95. His optical vision is 20/710. The limiting factor is his neurological vision, but with optical correction, the best we can do is go from 20/710 to 20/95, a very substantial improvement.
Here is the report I just received today by way of David’s residential program from the optometrist they took him to (click for full size):
And here is the yet unanswered email to the optometrist …
Attached is the Vision Consultation form that you appear to have filled out for my son, David, concerning his exam by you on January 24, 2011 of this year. I have a question and some concern about the only note that is written on the form.
It says “Eyeglasses may assist in near vision, but not mandatory” (emphasis as on the original)
The first part of that I understand says that in your opinion you do not know if optical correction with eyeglasses would assist David in his near vision. Am I correct? Obviously they would not help with his neurological issues and his partially compromised optic nerve, but he does have optical issues as well.
More importantly, you appear to say that eyeglasses are “not mandatory.” They are not mandatory for … what? For something to be mandatory it must fulfill a need or be needed to obtain a goal (i.e., meet legal requirements, enable an action, etc.). It seems to me that you are saying his glasses are no longer mandatory for him to reach some goal you have set or you are using for his vision.
SPECIFICALLY, what goal has been set for David, with respect to his vision, for which optical correction is not mandatory?
Thank you for your time and attention.
Very simply, the goal for David has always been to provide him with the best opportunity to maximize his visual potential. There is no way the staff will bother with eyeglasses when told they are not mandatory by the consulting optometrist.
I’ll keep you posted …