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Jordan Michael Murray, Fatema Firoz Ghasia; Gaze holding in Amblyopia: Binocular versus Dichoptic Viewing conditions. Invest. Ophthalmol. Vis. Sci. 2020;61(7):512.
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© ARVO (1962-2015); The Authors (2016-present)
Amblyopia is increasingly regarded as a binocular disorder with increasing interest in newer dichoptic therapies that encourage the coordinated use of the two eyes, which have produced mixed results. We have previously reported abnormal fixation eye movements particularly of the amblyopic eye. The purpose of the study was to assess the fixation stability of the amblyopic eye in dichoptic environment when the contrast of the fellow eye was rebalanced to facilitate reduction in the inter-ocular suppression.
We recruited 8 amblyopic and 4 control subjects. Eye movements were measured with high-resolution video-oculography during binocular and dichoptic viewing conditions. In the binocular gazeholding task, a white dot subtending .5 degrees against a black background was displayed 55cm in front of a subject who fixated on the dot for 45 seconds. In the dichoptic gazeholding task, the dot is presented independently but coincidently to each eye using a haploscope. The brightness of the fellow eye dot is varied over four 45 second intervals. Fast and slow eye movements and BCEA of fellow and amblyopic eye were analyzed. Vergence BCEA, a measure of disconjugacy, was computed.
We found increased instability in both controls and amblyopes under dichoptic viewing in both eyes, especially at low fellow eye contrasts. BCEA values increased from .751 (.13) to .850 (.08) at 100% contrast in the dichoptic environment with no significant change as contrast was decreased in controls. Amblyopes responded more dramatically, with mean BCEA values increasing from 1.67 (.94) to 2.94 (1.38) 100% contrast and 6.46 (3.84) under low contrast conditions. Dichoptic viewing also affected eye alignment, with 4 of the 6 strabismic subjects experiencing pronounced increases in strabismus angle compared with binocular viewing. Vergence BCEA inreased from 1.93 (.925) to 3.15 (2.99) at 100% contrast in amblyopes, rising to 4.84 (3.31) at low contrast. Controls dropped from 1.004 (.314) to .863 (.107) at 100% and to .622 (.264) at low contrast.
Even for simple stimuli dichoptic presentation presents challenges for amblyopes. Although the contrast rebalance to the fellow eye is likely reducing the inter-ocular suppression, the eye misalignment and disconjugacy are increased in the dichoptic environment for amblyopic subjects. This could account for the variability of treatment outcomes seen with dichoptic therapies.
This is a 2020 ARVO Annual Meeting abstract.
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