On the maintenance of normal ocular dominance and a possible mechanism underlying refractive adaptation

Abstract

Purpose. Do humans with uncorrected anisometropia who have not developed anisometropic amblyopia exhibit a shift in ocular dominance nonetheless, reflecting a more subtle form of deprivation? Also, is such a change in dominance, if it occurs, permanent or could it be rectified by an extended period of optical correction? Methods. A total of 25 normal controls (27.5 ± 2.1 years; mean ± SD); 28 anisometropes (20.7 ± 5.6 years) who were fully corrected for more than 16 weeks prior to this investigation; and 24 anisometropes who had never been corrected (21.2 ± 9.8 years) participated in this study. Sensory eye dominance of observers was measured using the binocular phase combination paradigm to find an interocular contrast ratio at which the contributions of each eye to the binocularly fused percept were equal (i.e., the balance point measure of ocular dominance). Results. Controls exhibited a balance point close to unity (0.91 ± 0.05), while the two groups of anisometropes exhibited a clear binocular imbalance (uncorrected anisometropes, 0.51 ± 0.28; corrected anisometropes, 0.70 ± 0.19); both were significantly different from controls (P < 0.001). The imbalance was less severe in corrected anisometropes compared with uncorrected anisometropes (P = 0.004). Conclusions. We find that anisometropia is associated with an ocular imbalance even in the absence of amblyopia. This abnormality is weaker in anisometropes who have worn an optical correction for some time, suggestive that a better optical status leads to a better binocular status.