Examination of Anti-Suppression Therapy for Amblyopia

Amblyopia, a developmental disorder associated with abnormal early visual experience, is defined by a deficit in visual acuity in the amblyopic eye (AE) which cannot be optically corrected. Although some research on amblyopes suggested visual information from the eyes is not combined, a growing body of studies report that binocular mechanisms are intact, but suppressed. Using dichoptic presentation of stimuli of relatively high and low contrasts to AE and non-AE, respectively, Hess et al. (2010, Optometry & Vision Science) demonstrated that binocular perceptual training can reduce suppression from the non-AE and improve visual acuity and stereoacuity. We examined the influence of binocular perceptual learning on the visual acuity, crowding, stereovision, binocular motion coherence thresholds, and binocular integration in five individuals with severe amblyopia. Binocular integration was measured as the contrast at which noise dots presented to the non-AE influenced the perception of the direction of motion of the signal dots in the AE. Initially, participants demonstrated visual acuity in the AE greater than 1.0 logMAR and nonmeasureable stereoacuity. Whereas 2 participants demonstrated suppression on the Worth 4-dot test, 4 participants evidenced suppression on the binocular integration task. After training on the binocular integration task for 20 to 24 hours, all participants reported better vision and increased ability to focus with the AE, which were supported by better visual acuity (t(4) = 14.3, p < 0.05) and less crowding (t(4) = 2.8, p < 0.05). In contrast, neither stereoacuity measured on the Randot tests nor suppression measured on the Worth 4-dot test improved. The influence of binocular perceptual training on binocular motion coherence thresholds and binocular integration evidenced individual variation. Our data are consistent with those of previous studies indicating that perceptual training can benefit adult amblyopes' visual experience.