# Optical Forums > Ophthalmic Optics >  Surprising(?) results from best visual acuity study

## rinselberg

_... the lesson of this study is that it was not the subjects with the best optics in their visual systems who had the [highest] 20/9 vision, it was the people with the best "computer software" in their sensory systems filtering out the optical aberrations. 

The computer software is evidently the limiting factor in our vision, not the optical performance and the aberrations present in our eyes ... This is a big shift in our concept of how the visual system works, and it has practical implications on what we should be doing._

The figurative term "computer software" is used in the article to describe the neural processing that takes place within the occiptial cortex of the brain - processing that is a neural response to the visual sensory data that the brain receives from the retina(s).

The article is fairly summary, and just about two or three pages long:
http://www.osnsupersite.com/default.asp?ID=11906

If you click on this link (above), it will probably ask you to register online (it's free of charge) before you can access the article. They send you a daily email with a summary of what's new on the website. I haven't noticed any increase in my email spam since I registered at this website several months ago.

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## Darryl Meister

How did they measure the optics of the eye? Did they consider the density of the retinal receptors (Hartridge's criterion), the diffraction limits of the optics (Rayleigh's criterion), the aberrations of the optics, or the scatter of ocular media of the eye for each subject?

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## rinselberg

_Recent work by Pablo Artal, PhD, and colleagues in Spain has shed interesting light on the process of neural adaptation, Dr. Holladay noted. He said Dr. Artal held a contest at his university, offering a $300 award for the person with the best visual acuity. Anyone with visual acuity of 20/20 could enter the contest. More than 300 students participated, and among those three people with 20/9 vision were identified. (The best vision ever recorded was 20/8, Dr. Holladay said.) 

Dr. Artal performed two studies with these subjects. He began by measuring their wavefront aberrometry and plotting each persons point spread function (PSF) vs. their visual acuity. 

The PSF should look like a point, Dr. Holladay said, and if it looks like a cobweb or a triangle, thats what the patient actually sees when they look at a star or a single LED, rather than a point. 

He continued, The remarkable thing is, those people with the best PSF were not the ones that had the 20/9 visual acuity. In fact, people with cobwebs as their PSF were the ones that had the 20/9 visual acuity. Those with the single point PSF were downstream, with visual acuities between 20/16 and 20/20. There was no correlation between performance by wavefront aberrometry and the best visual acuity._

More from the article for you, Darryl ...

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## Ian Jordan

Everyone optical professional should know that refraction and lens design is only part of the optimisation of vision. There are many cases in which some lenses are inappropriate and standard treatment involves trying to make the system work better e.g. using contact lenses in equalising image size in amblyopia treatment.
There is much more to a presciption than the refractive power and lens design - otherwise why are there non tolerance to seemingly identical lenses. The Rx is *not* an accurate refraction in all circumstances, only those in the eye examination room e.g. myopic shift - it is in fact a "best interpretation" of the best lens for most applications.
Those who can will also take into account retinal and cortical mapping, temporal processing, sequencing, LMS pathway modification etc, parvo and magno integration, fusional area plasticity. Acuities are often markedly better than with the "best" design lenses.

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## Darryl Meister

It sounds like the author took little more than the point spread function into consideration. This is certainly a good start, but not the sole factor that affects the quality of the retinal image. The PSF will also vary with pupil size, accommodation, and so on, but they might have factored this in. Still, additional physiological considerations, such as the density of the receptive fields, will also play a role. While there is no doubt that the neural processing involved with vision accomplishes some pretty extraordinary feats, I don't know that the author has investigated this critically enough to draw any conclusions, one way or the other. Still a good discussion though.

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