The Effect of Long Term Monocular Occlusion on Vernier Threshold: Elasticity in the Young Adult Visual System.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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Five subjects ages 19-22 were monocularly occluded for six days. Their verneir thresholds and fixation integrity measurements using a modified Haidingers brush were determined at pre-occlusion, two, four, and six days of monocular occlusion, and 24 hours after patch removal. The occluded eye demonstrated a significant rise in vernier threshold after the two day occlusion period.l The threshold continued at that level throughout the six day occlusion period before returning to normal within 24 hours after removal of the patch. The non-occluded eye did not show a matching enhancement effect characteristic of the competition model. Every subject also manifested an amount of eccentric fixation in the occluded eye. The eccentric fixation did not generally increase with time occluded, but did show an elastic response by returning to normal foveal fixation in 24 hours. The decrement in verneir performance in the occluded eye is probably best explained as a temporary elastic eccentric fixation rather than the loss of channels as theorized in the competition model. Our data did indicate a faster drop off of verneir acuity with retinal eccentricity than did the interpolated data of Westheimers 1979 postulating that a secondary process was also contributing to the rise in threshold. The secondary process could possibly be either a loss of neural channels or an instability of fixation after patch removal.
- Anatomy and Physiology