Spatial-frequency dependent binocular imbalance in amblyopia.

Miyoung Kwon,Emily Wiecek,Steven C Dakin,Peter J Bex

doi:10.1038/srep17181

Abstract

While amblyopia involves both binocular imbalance and deficits in processing high spatial frequency information, little is known about the spatial-frequency dependence of binocular imbalance. Here we examined binocular imbalance as a function of spatial frequency in amblyopia using a novel computer-based method. Binocular imbalance at four spatial frequencies was measured with a novel dichoptic letter chart in individuals with amblyopia, or normal vision. Our dichoptic letter chart was composed of band-pass filtered letters arranged in a layout similar to the ETDRS acuity chart. A different chart was presented to each eye of the observer via stereo-shutter glasses. The relative contrast of the corresponding letter in each eye was adjusted by a computer staircase to determine a binocular Balance Point at which the observer reports the letter presented to either eye with equal probability. Amblyopes showed pronounced binocular imbalance across all spatial frequencies, with greater imbalance at high compared to low spatial frequencies (an average increase of 19%, p < 0.01). Good test-retest reliability of the method was demonstrated by the Bland-Altman plot. Our findings suggest that spatial-frequency dependent binocular imbalance may be useful for diagnosing amblyopia and as an outcome measure for recovery of binocular vision following therapy.

Highlights

While amblyopia involves both binocular imbalance and deficits in processing high spatial frequency information, little is known about the spatial-frequency dependence of binocular imbalance
The balance point (BP) was estimated by fitting the data with a Weibull function and finding the contrast ratio corresponding to a 0.5 proportion of weak eye responses
We found that the BP of the amblyopia group significantly differed across different spatial frequency (SF) (F(3, 33) = 14.11, p < 0.001) while that of the normal control group remained constant across different SFs (F(3,33) = 2.55, p = 0.073)

Summary

Introduction

While amblyopia involves both binocular imbalance and deficits in processing high spatial frequency information, little is known about the spatial-frequency dependence of binocular imbalance. Recent treatment regimens designed to reduce suppression by promoting an exposure to binocularly balanced stimuli have been shown to improve visual acuity and stereoacuity[28,29,30,31] These observations suggest that addressing the imbalance in monocular signals may restore normal binocularity in amblyopia. A considerable literature indicates that core amblyopic deficits such as contrast sensitivity loss and spatial distortion exhibit spatial-frequency dependency. Hess and Bradley[39] reported that amblyopia does not influence supra-threshold apparent contrast at any SF, suggesting that gain control mechanisms compensate for deficits at detection threshold[40] This distinction between threshold and supra-threshold contrast perception in amblyopia raises fundamental questions concerning the SF dependence of binocular interactions. No clinical assessment is currently available for quantifying such SF-dependent binocular imbalance

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