Binocular luminance summation in young kittens and adult strabismic cats.

Normal adult cats show a 35% increase in pupil diameter when one eye is illuminated and the other occluded, rather than when both eyes are illuminated. Young kittens show significantly less binocular luminance summation than adult cats (14%). Since these kittens also show a significantly reduced pupillary response to luminance decrements, the postnatal development of binocular luminance summation reflects an increase in pupillary motility, rather than a development of binocular function. Binocular luminance summation is much reduced in esotropic cats (6%), but not in exotropic cats (33%). This finding casts doubts on the usefulness of binocular luminance summation as a measure of binocular function.