Binocular combination in anisometropic amblyopia

Abstract

Using a suprathreshold binocular summation paradigm developed by J. Ding and G. Sperling (2006, 2007) for normal observers, we investigated suprathreshold cyclopean perception in anisometropic amblyopia. In this paradigm, two suprathreshold sinewave gratings of the same spatial frequency but different spatial phases are presented to the left and right eyes of the observer. The perceived phase of the binocularly combined cyclopean image is measured as a function of the contrast ratio between the images in the two eyes. We found that both eyes contributed equally in normal subjects. However, stimulus of equal contrast was weighted much less in the amblyopic eye relative to the fellow eye in binocular combination. For the five amblyopes, the effective contrast of the amblyopic eye in binocular combination is equal to about 11%–28% of the same contrast presented to the fellow eye, much less than the ratio of contrast sensitivity between the two eyes (0.73–1.42). The results from the current study have many important implications in amblyopia research and treatment.

Effects of Anisometropic Amblyopia on Visuomotor Behavior, Part 2: Visually Guided Reaching

“…Anisometropic amblyopia was defined as amblyopia in the presence of a difference in refractive error between the two eyes of Ն1 diopter (D) of spherical or cylindrical power. 20,21,[23][24][25][26] All patients had visual acuity between 20/30 and 5/400 in the amblyopic eye, 20/20 or better in the fellow eye, and an interocular acuity difference Ն2 lines. Eleven patients had mild amblyopia (visual acuity of 20/30 to 20/60) and fine to gross stereopsis, whereas three had severe amblyopia (visual acuity of 20/400 to 5/400) and no stereopsis.…”

Assessing Binocular Interaction in Amblyopia and Its Clinical Feasibility

“…It is the most common cause of monocular visual loss in children, and affects approximately 3–5% of the population [2]. While amblyopia is associated with a wide range of monocular and binocular visual deficits that include reduced visual acuity [3], loss of contrast sensitivity [4], spatial distortion [1], impaired contour integration [5], abnormal binocular interaction [6], [7], abnormal motion perception [8] and visual-motor deficits [9]–[13], visual acuity remains the main clinical measure for diagnosis and treatment outcomes. Despite the success of penalization and occlusion therapies in improving monocular acuity in the amblyopic eye, the monocular treatment approach has been challenged by high occurrences in residual and recurrent amblyopia [14], hinting that amblyopic vision cannot be fully characterized by a single visual acuity measure.…”

“…Recent population studies have shown that abnormal binocular visual experience, represented by interocular differences in refractive error and poor stereoacuity are good predictors of residual amblyopic deficits [14]–[16]. Furthermore, psychophysical studies have shown the existence of binocular summation in amblyopia under some conditions, at both threshold [17], [18] and suprathreshold levels [7], [19]–[23]. Such interactions are best revealed by compensating for the contrast sensitivity deficit of the amblyopic eye, or equating the effective contrast of the two eyes.…”

Contrast gain-control in stereo depth and cyclopean contrast perception

“…With a single parameter, the model successfully accounted for 95% of the variance for 48 combinations of phases and contrasts in their experiments. The paradigm and the model were adopted by Huang et al (2009) to study suprathreshold cyclopean perception in anisometropic amblyopia, finding that stimulus of equal contrast was weighted much less in the amblyopic eye relative to the fellow eye in binocular combination. Huang et al (2010) adopted the Ding-Sperling paradigm but measured both perceived contrast and phase of cyclopean images in 90 combinations of base contrast, interocular contrast ratio, eye origin of the probe, and relative phase.…”

“…The multipathway contrast gain-control model (MCM), previously developed for binocular contrast and/or phase combination (Ding & Sperling, 2006Huang, Zhou, Lu, Feng, & Zhou, 2009;Huang, Zhou, Lu, & Zhou, 2011;Huang et al, 2010), was elaborated to simultaneously account for disparity thresholds and perceived contrasts of the cyclopean images. The model also accounted for some challenging data on stereo depth perception in the literature (Cormack et al, 1991;Ding & Levi, 2011;Legge & Gu, 1989).…”