Re: An eye exam

[Ludwik Kowalski <kowalskiL@MAIL.MONTCLAIR.EDU>]

John Clement wrote:

> ... I am surprised that the effect [vision with two eyes being
> better than with each eye alone] was discovered only in the 90s...

Me too. But more surprising is the effect itself, it seems to
contradict the common "blurred retinal image" explanations.
If one retinal image is strongly blurred (due to astigmatism,
myopia or hyperopia) while another is sharp then how the
two-eyes vision can lead to a better recognition of details?
The blurred image explanation of visual defects can not be
wrong; it is validated by successful eyeglass industry. (If
I recall correctly eyeglasses were already used in Europe
in 12th century.)

But some secondary effects, not accounted by geometrical
optics, may dominate when both eyes are nearly the same.
What is the mechanism of the two eyes cooperation? I do
not know. The obvious analogy is a weight suspended by
two strings; each string would break under the load but
two strings are able to hold it. At which extreme is the
two-eyes cooperation more pronounced; when both retinal
images are very good or when they are both very bad? I
suspect that the level of illumination (day vision versus
evening vision) is likely to be a factor in this effect. An
"extra-credit" project for a group of students? Why not.
Ludwik Kowalski

> This URL leads one to expect an 11% or  a half  line
> improvement on a visual chart on average for binocular
> versus monocular testing.
>
>    <http://www.lighthouse.org/research_acuity.htm>
>
> Brian Whatcott