Visual Acuity May Not Indicate Success in Anisometropic Amblyopia Treatment

Patients treated for anisometropic amblyopia who regain normal visual acuity (VA) may have normal monocular temporal synchrony thresholds, but still exhibit abnormally large dichoptic temporal synchrony thresholds compared with individuals with emmetropia, according to research published in Ophthalmic and Physiological Optics. 

Researchers included 14 patients (mean age, 23.17 years; best-corrected visual acuity [BCVA], ≤0.1 logMAR) who underwent patching therapy for unilateral anisometropic amblyopia and 15 age-matched controls (mean age, 24.40 years) with emmetropia in the study. The team presented 2 pairs of flickering Gaussian dots (1 Hz) as visual stimuli — a reference pair that flicked synchronously and a signal pair that flicked asynchronously. Participants determined whether the position of the asynchronous pair was above or below fixation. The investigators measured the temporal synchrony threshold under both monocular and dichoptic viewing conditions and defined temporal synchrony threshold as the minimum degree of the temporal phase at which a participant could differentiate a signal pair. 

Under monocular viewing conditions, the temporal synchrony thresholds of eyes treated for anisometropic amblyopia and fellow eyes were not significantly different (P =.15). Under dichoptic viewing conditions, the temporal synchrony threshold in patients treated for anisometropic amblyopia was significantly higher compared with the control group (119.34 vs 99.78 ms; P =.009). 

There was no significant association between the amblyopic monocular and dichoptic viewing conditions in patients treated for amblyopia (r, −0.22, P =.94), according to the report.

“[T]reated anisometropic amblyopes with normalized VA still exhibit deficits when detecting the temporal asynchrony of signals between the eyes despite having regained normal monocular VA,” according to the researchers. “This questions the traditional use of VA recovery as the hallmark of therapeutic success. Residual spatio-temporal binocular deficits remain even when the acuity deficit has been resolved.”

Study limitations include a small sample size and the narrow age range of participants.