The effects of Monocular Training on Binocular Functions in Anisometropic Amblyopia.

PURPOSE: It's been shown that intensive monocular perceptual learning can improve visual acuity, contrast sensitivity, and vernier acuity in the amblyopic eye in adults with amblyopia. It is however not clear how much monocular training can enhance binocular visual functions. In the current study, we aimed to evaluate effects of monocular training on a variety of binocular functions.

METHODS: Nineteen anisometropic amblyopes (18.5±1.26 yrs) were trained in a grating contrast detection task near each individual's cutoff spatial frequency for 6 to 10 days (630 trials/day). Visual acuity, stereoacuity, monocular and binocular contrast sensitivity functions (CSF), binocular phase combination and binocular rivalry were tested before and after training.

RESULTS: Training substantially improved contrast sensitivity at the trained spatial frequency (by 67.8%) and a wide range of untrained spatial frequencies (84.0% on average), logMAR acuity (from 0.51 to 0.34; about 2 lines) in the amblyopic eye, and stereoacuity from 929.1" to 80.4". Training also significantly improved the dominance duration of the amblyopic eye (from 9% to 15%) in binocular rivalry through elongation of each dominant phase without changing switching frequency between the two eyes. On the other hand, training didn't significantly improve the ratio of the areas under CSF between binocular and monocular (fellow eye) viewing (1.16 vs 1.11, p>0.1) and the interocular balance point, i.e. the contrast ratio at which the two eyes contribute equally to binocular phase combination (0.14 vs 0.16, p>0.10). There was no significant correlation between improvements in visual acuity, stereoacuity, and binocular rivalry.

CONCLUSIONS: Although monocular training can improve visual acuity and contrast sensitivity and eye dominance of the amblyopic eye, the magnitudes of improvements didn't correlate with each other; the impact of monocular training on binocular phase combination was not significant. The results strongly suggest that structured monocular and binocular training is needed to fully recover deficient visual functions in anisometropic amblyopia.