astereopsis (was Re: Vision problem and Virtual Reality)

Matthew Belmonte mbelmont at sdcc3.ucsd.edu
Fri Nov 20 21:35:15 EST 1992

In article <crystal.722283589 at glia> crystal at glia.biostr.washington.edu (Crystal)

>Her post-operative treatment is an eye 
>cream that contains cholinesterase (sp?), an inhibitor to acetylcholine
>in some post-synaptic neuron that somehow strengthens the eye muscles (or
>at least that was what she told me - this could be in error - please 
>correct it)

Acetylcholinesterase catalyses the degradation of acetylcholine (the
neurotransmitter at the neuromuscular junction) into acetate and choline.  It
occurs naturally in the synaptic cleft; without it, the postsynaptic cell would
stay depolarised for a very long time.  The addition of acetylcholinesterase
would weaken the muscle, not strengthen it.  Since the extraocular muscles are
set up as opponents, though, I guess this would have the desired effect since
it'd lower the difference in tension between the two recti.

As for lack of stereopsis, it's extremely common, and many (if not most) people
who lack stereopsis don't know that they lack stereopsis.  I can't remember
where I read it, but I seem to remember some text mentioning that about 10% of
the population doesn't have stereo vision.  In most activities this makes almost
no difference; the visual system is very good at inferring the third dimension
from two-dimensional cues such as relative size, shading, and obscurement.  The
revelation that a person lacks stereopsis usually evokes surprise and a sense of
wonder about what it must be like to see `true' 3-D.

I've always had difficulty getting my eyes to point at the same place---often
when I'm reading and especially when I'm tired---and for a long time I wondered
what I was doing wrong because I never could get any of those nifty stereograms
to work.  It was only when I started studying neuroscience that I realised that
I really have no 3-D vision.  Groovy, huh?  (The eye-pointing problem seems to
have got worse as I've got older---too many late nights with the neuroscience
literature :-)
Matthew Belmonte	mbelmonte at ucsd.edu
`The Bohemian Kingdom' - Risley Residential College for the Creative and
Performing Arts, Ithaca, New York

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