T3D Re: Interocular question

[roberts@xxxxxxxxxxxxxxxxx (John W Roberts)]

>Date: Tue, 9 Mar 1999 22:26:01 -0700
>From: Bruce Springsteen <bsspringsteen@xxxxxxxxx>
>Subject: T3D Re: Interocular question

>Measuring my own interpupillary with a mirror and a ruler seemed an
>easy trick at the time, but I wonder if I was wrong.  Is that too
>imprecise a method for +/- .5mm accuracy?  Just a side question.

If the eyes are converged at a distance closer than infinity, the
interpupillary distance will be decreased, which may affect the accuracy
of the measurements. I don't know what methods people have traditionally
used, but here's a possible method to avoid convergence errors:

 1) Face your reflection directly in a mirror.

 2) "Parallel view" your eyes, so that the image of the two eyes is merged
    to form an image of a third eye in the mirror. (This orients your eyes
    so that the axes of view are parallel.)

 3) Take two pens or other identical pointed objects, and hold the points
    up against the surface of the mirror.

 4) Move the two pens so they also form a merged image in the mirror, with
    the merged point exactly over the center of the pupil of the merged eye
    image. Hold the pens there.

 5) Using a ruler, measure the distance between the two pen points. (You can
    have someone else take the measurement, or perform the experiment with the
    pens placed along the edge of a ruler, and just read the distance on
    the ruler.)

The distance measured should match the interpupillary distance with 
convergence at infinity.

Comments?

John R


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