Abstract: PURPOSE: To investigate whether adults with anisomyopia exhibit binocular imbalance across a wide range of spatial frequencies and examine whether this imbalance can be rectified with optical correction.
METHODS: 15 anisomyopes (24 ± 0.9 years), 15 isomyopes (23.6 ± 1.3 years) and 14 emmetropes (22.5 ± 2.9 years) participated in this study. A balance point, which is an interocular contrast ratio when both eyes’ contributions to binocular fusion are equal, was measured using binocular orientation combination task at 0.5,1,2 and 4 cycles per degree (c/d). The binocular balance was quantitatively assessed as the absolute value of BP on log scale (|BP|). Using the data, we fit a slope from simple linear regression to better capture the dependence of binocular balance as a function of spatial frequency. Moreover, we computed the area under a curve (AUC) as an index of imbalance across spatial frequency. All the subjects with anisomyopia and isomyopia were tested twice with and without optical correction.
RESULTS: |BP| of all groups significantly increased as a function of spatial frequency (P < 0.05). For uncorrected groups, |BP|, slopes and AUCs of anisomyopes were all significantly different from the two other groups (P < 0.05). The interaction between whether correction and spatial frequency was also significant (F (3,42) = 8.48, P < 0.05). |BP|, slopes and AUCs of uncorrected anisometropia were statistically larger than those in the corrected state (P < 0.05). There was no significant difference between myopes and emmetropes.
CONCLUSIONS: Anisomyopes exhibit clear binocular imbalance as a function of spatial frequency. Optical correction improves the imbalance but the degree of improvement depends on spatial frequency. Our results show that binocular imbalance in anisomyopia occurs in ocular region instead of the later sites of visual pathway.

Key words: anisomyopia, binocular balance, spatial frequency