BINOCULAR CONTRAST SUMMATION AND INHIBITION IN AMBLYOPIA - THE INFLUENCE OF THE INTEROCULAR DIFFERENCE ON BINOCULAR CONTRAST SENSITIVITY

The monocular contrast sensitivity loss in amblyopia is well documente d. We investigated the influence of interocular sensitivity difference on binocular contrast sensitivity in amblyopia. Monocular and binocul ar contrast sensitivity functions of six amblyopes (three strabismic a nd three anisometropic) were measured. The monocular contrast sensitiv ity loss depended on the type of amblyope. Anisometropic amblyopes gen erally showed high frequency losses. Strabismic amblyopes showed losse s at both low and high spatial frequencies. Binocular performance was assessed in terms of binocular ratios (binocular/non-amblyopic). A bin ocular ratio greater than 1 indicates binocular summation (binocular > monocular) while a ratio less than 1 shows binocular inhibition (bino cular < monocular). In all subjects, the binocular ratio depended on t he difference between the amblyopic and the non-amblyopic eye. Minimal interocular difference produced binocular summation, the magnitude of which decreased as the difference between the two eyes increased. Fur ther increases in the monocular difference produced binocular inhibiti on. Anisometropic amblyopes showed a greater degree of binocular summa tion at low spatial frequencies compared to strabismic amblyopes. Both types of amblyopes showed binocular inhibition at high spatial freque ncies. Clinical implications of binocular summation and inhibition in amblyopia are discussed.