Temporal synchrony discrimination is abnormal in dichoptic but not monocular visual processing in treated anisometropic amblyopes.

Purpose: To evaluate whether temporal synchrony processing deficits remain when normal visual acuity is restored in adults with unilateral anisometropic amblyopia.

Methods: We recruited 14 clinically treated anisometropic amblyopes (mean age 23.17 ± 2.53 years) with best-corrected visual acuity ≤ 0.1 logMAR and 15 age-matched emmetropes (mean age 24.40 ± 1.92 years) with normal vision to participate in our experiment. We presented two pairs of flicking Gaussian dots (1 Hz) as visual stimuli: one pair of dots was synchronous (reference), and the other pair of dots was asynchronous (signal). Subjects were asked to determine the position of the asynchronous pair. We applied the constant stimuli method to measure the temporal synchrony threshold under monocular and dichoptic viewing conditions. There were eight temporal phase lags in the asynchronous pair. The minimum degree of the temporal phase at which a participant can discriminate a signal pair is defined as the temporal synchrony threshold.

Results: Under monocular viewing conditions where both the reference and signal pairs were presented to one eye, the temporal synchrony thresholds of previous amblyopic eyes and fellow eyes were not significantly different (p = 0.15). Under dichoptic viewing conditions where both the reference and signal pairs were dichoptically presented to both eyes, the temporal synchrony threshold in the treated anisometropic amblyopes was significantly higher than that of the controls (119.34 ± 20.43 vs. 99.78 ± 16.60 ms, p = 0.009). There was no significant correlation between the monocular and dichoptic viewing conditions in the treated amblyopes (r = -0.22, p = 0.94).

Conclusions: Temporal synchrony discrimination is abnormal under dichoptic but not under monocular visual stimulation in treated anisometropic amblyopes with normalised visual acuity.