T3D Re: A Third Simple On

[abram klooswyk <abram.klooswyk@xxxxxx>]

Greg Wageman (28 Sep 1998 t3d Digest 369):
>Even though the eye's lens has lost its flexibility
>and can no longer accommodate, the muscles are still trying, aren't
>they?  So in spite of the inability to change accommodation, one might
>still experience the related eyestrain the same as though one could,
>yes?

I have pondered on that also. I remember having read a paper in which 
was said that (in elderly ?) the accommodation muscles stretch the
retina - 
I don't remember the exact wording or point of it, nor the source, but 
this indeed would mean that the muscles go on trying.
  (By the way, remember that *relaxation* of the accommodation muscles 
   in the young means a more spherical eye lens, focused nearer)

I believe that it has not been proven that the effect we considere now 
is the only or even the main source of 'eyestrain', wich in itself is a
vague notion. Visual scientists, as I know them (:-)), pay very little
attention to comfort (in their publications...). In fusion experiments 
sometimes remarkable figures come out, but hardly ever is said how many 
persons got headache.

But if the accommodation-convergence link IS important, it is illogical 
to suppose that, beacause "the muscles go on trying" elderly would not 
benefit from the decline of the accommodation range.
First, accommodation IS for providing sharp images, and the main cue for 
accommodation change is blur. 

Now if eyestrain (in stereo viewing) in young people results from two 
conflicting 'forces' on accomodation:
1. convergence-induced accommodation (although the link is not so tight
   as some people believe), leading to blur in stereo viewing,
2. blur-driven accommodation (the main 'force' on accommodation), which
   restores definition,
then obviously the latter is absent in the elderly, if they wear the
right 
glasses or adjust the viewer properly. 

But, when the accommodation muscles go on following convergence in the 
elderly, there is nothing wrong: this is normal in natural vision! But 
in *them* it does *not* lead to blur, as it would do in the younger, 
so no conflict arises, so no eyestrain. 

Be patient and go on living, I would say.

Abram Klooswyk


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