P3D Dark Vergence (was: Curious eye defect)

[Andrew Woods <andrew@xxxxxxxxxxxxxxxxxxxxx>]

Bob Wier <wier@xxxxxxxxxxxxxxxxx> wrote:
>In my last eye exam, I ran into something like this - the guy said
>something like "Is the red dot inside the box" (or whatever, I don't
>recall exactly). I replied "It can be - do you want me to do that?"
>He responded "What?", so I explained that I could freeview and cross
>eye and that basically I had no particular pre-conceived notion of
>where an image ought to be (based on convergence/divergence...).

(I may not have this absolutely correct, but...) This test is performed to
measure a person's resting point of vergence (or dark vergence).  The 
individual tightnesses of an individual's eye muscles dictate at what
eye vergence the eyes will rest at.  The only way to test this is 
to switch off a person's stereoscopic vision.  The apparatus used to test
this will usually show one eye a scale and the other eye will see a red dot
(or red line).  By asking the person where the red dot appears on the scale,
you have a measure of their rest point of vergence.

Unfortunately, the measurement is biased by the accomodative (focus)
response of the eye and whether a person is a 3D nut (like me).

If a person has an extreme value of dark vergence, it can mean that the
person will have difficulty fusing on things close or fusing on things at
infinity.  This can be corrected with prisms in the glasses.

Ok, what's the relevance to 3D?

I have a half baked theory that an individual's value of dark vergence
(also known as Heterophoria) has some effect on whether they are more easily
able to view stereo-pairs in the cross-eyed or parallel formats.
I suspect if a person has esophoria (the tendancy of the eyes to turn in
when the stimulus of fusion is removed) then they will find it easier to
cross-view.
Similarly if a person has exophoria (the tendancy of the eyes to turn out
when the stimulus of fusion is removed) then they will find it easier to
parallel-view.
Like I said, still a theory...  I'd like to do some more research in this area.

Andrew Woods             http://info.curtin.edu.au/~iwoodsa


25 days to go to the Stereoscopic Displays and Applications Conference
             http://info.curtin.edu.au/~iwoodsa/stereoscopic


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End of PHOTO-3D Digest 2485
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