Pattern reversal VER as a tool for evaluating unbalanced visual inputs between the two eyes

Abstract

We studied the effects of unequal or unbalanced visual inputs on the binocular system of normal subjects by measuring the amplitudes of the binocularly and the monocularly recorded VER and determining the value of binocular summation. The stimuli used were patterns that were either fused or not fused, of unequal luminosity and of unequal image size. When identical patterns were delivered to each eye and the patterns were fused, the binocular VER demonstrated a larger amplitude than the monocular VER, resulting in a binocular summation that was prominent in the low-contrast stimulus pattern. With stimulus patterns of higher contrast, the amplitudes of the binocular and the monocular VER did not differ greatly, and the value of binocular summation was significantly decreased. When fusion was disturbed with a base-in prism, the binocular VER displayed smaller amplitudes than the monocular VER, indicating binocular interaction or inhibition. With a small interocular luminosity difference, the binocular VER exhibited a larger amplitude than the monocular VER (binocular summation), but as the difference exceeded a certain level (0.6 to 0.8 log units), the binocular VER amplitudes were smaller than those of the monocular VER (binocular inhibition). With very large luminosity differences, the binocular VER amplitudes were almost similar to those of the monocular VER (suppression). When the perceived image size of the retina was altered with an aniseikonic lens, the binocular VER displayed larger amplitudes than those of the monocular VER (binocular summation) in aniseikonia equal to or less than 3.0%. At 5.0% aniseikonia, the binocular VER amplitudes were almost equal to the monocular VER (zero summation). At aniseikonia equal to or larger than 8.0%, the binocular VER amplitudes were significantly smaller than those of the monocular VER (binocular inhibition or interaction).