Perceptual learning improves stereoacuity in amblyopia

Abstract

Purpose: Amblyopia is a developmental disorder that results in both monocular and binocular deficits. Although traditional treatment in clinical practice (i.e., refractive correction, or occlusion by patching and penalization of the fellow eye) is effective in restoring monocular visual acuity, there is little information on how binocular function, especially stereopsis, responds to traditional amblyopia treatment. We aim to evaluate the effects of perceptual learning on stereopsis in observers with amblyopia in the current study.

Methods: Eleven observers (21.1 ± 5.1 years, six females) with anisometropic or ametropic amblyopia were trained to judge depth in 10 to 13 sessions. Red-green glasses were used to present three different texture anaglyphs with different disparities but a fixed exposure duration. Stereoacuity was assessed with the Fly Stereo Acuity Test and visual acuity was assessed with the Chinese Tumbling E Chart before and after training.

Results: Averaged across observers, training significantly reduced disparity threshold from 776.7″ to 490.4″ (P < 0.01) and improved stereoacuity from 200.3″ to 81.6″ (P < 0.01). Interestingly, visual acuity also significantly improved from 0.44 to 0.35 logMAR (approximately 0.9 lines, P < 0.05) in the amblyopic eye after training. Moreover, the learning effects in two of the three retested observers were largely retained over a 5-month period.

Conclusions: Perceptual learning is effective in improving stereo vision in observers with amblyopia. These results, together with previous evidence, suggest that structured monocular and binocular training might be necessary to fully recover degraded visual functions in amblyopia. Chinese Abstract.

Keywords: amblyopia; perceptual learning; stereoacuity.

Figure 1

(A) Three textures used in the experiment. (B) Schematic illustration of stereo training task. In this example, the red component of the upper texture was shifted to right relative to its green counterpart to create an uncrossed disparity; the lower texture has zero disparity. The correct response is to press the down key in the keyboard to indicate the lower texture is the nearer one.

Figure 2

Individual and group average learning curves. Stereo training significantly reduced disparity threshold for 9 of 11 amblyopic observers over 10 to 13 training sessions. The group data were computed by averaging across the 10 common sessions of the 11 observers. Data were fitted with a Log-linear function. Error bars: ±1 SE.

Figure 3

Posttraining measures of visual acuity and Titmus stereopsis versus pretraining counterparts. The dashed line is the identity line (slope = 1; i.e., no improvement).