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MiYoung Kwon, Emily Wiecek, Steven C. Dakin, Peter J. Bex; A novel method to quantify spatial-frequency dependent binocular imbalance in amblyopia . Journal of Vision 2014;14(10):958. doi: https://doi.org/10.1167/14.10.958.
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© ARVO (1962-2015); The Authors (2016-present)
Abnormal binocular experience during early development often puts the visual system at risk of developing amblyopia. Binocular imbalance of the amblyopic eye is a core deficit in amblyopia. While studies of contrast detection-threshold have suggested that amblyopic eyes show more pronounced deficits at high than low spatial-frequencies, supra-threshold apparent contrast may be unaffected at any spatial-frequency (Hess & Bradley, 1980). Recent evidence suggests that binocular imbalance may be visual-field dependent (Babu et al., 2013), but little is known about its spatial-frequency dependence. We therefore introduce a novel method to assess binocular imbalance rapidly with a dichoptic letter-identification task. Test stimuli were band-pass filtered Sloan letters with peak spatial-frequencies of 1 to 15 cycles per degree. The letters are arranged in a layout similar to the ETDRS acuity chart (4 rows of decreasing letter size by 5 columns of varying letter contrast) on a gray background. A different letter chart is presented to each eye of an observer via stereo-shutter glasses. At each position, the identity and interocular contrast-ratio of the letter on each chart differs while the spatial-frequency content of the letter remains the same. Subjects were instructed to read aloud the chart in top-to-bottom and left-to-right order. The relative contrast of the letter in each eye is adjusted across several charts to determine the critical contrast-ratio of the amblyopic eye: defined as the interocular contrast-ratio required to report the letter in each eye with equal probability. The critical contrast-ratio of amblyopic eyes was significantly greater for high than low spatial frequencies (from 0.75 to 0.95) while no significant spatial-frequency dependent changes were found in normally-sighted subjects (from 0.55 to 0.60). Binocular imbalance in amblyopia is therefore spatial-frequency dependent. The finding suggests that our novel quantitative method holds promise for characterizing spatial-frequency dependent binocular imbalance in amblyopic vision.
Meeting abstract presented at VSS 2014
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