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Fatema F Ghasia, Jordan Murray, Kiran Garg; Fixation Eye Movements in Amblyopia during Binocular and Dichoptic viewing conditions. Invest. Ophthalmol. Vis. Sci. 2021;62(8):157.
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© ARVO (1962-2015); The Authors (2016-present)
Patching and dichoptic amblyopia therapies aid recovery of vision through distinct mechanisms and require different viewing conditions. We have previously characterized abnormalities of fixation eye movements of the fellow and amblyopic eye during monocular and binocular viewing conditions. The purpose of the study was to assess the fixation stability of the fellow and amblyopic eye and quantify eye misalignment in dichoptic environment when the contrast of the fellow eye was rebalanced to facilitate reduction in the inter-ocular suppression.
We recruited 20 amblyopic and 10 control subjects. Fixation eye movements were measured with high-resolution video-oculography during A) binocular and B) dichoptic viewing as the brightness of the fellow eye fixation target varied from full to low contrast. Fixation eye movements and BCEA of fellow and amblyopic eye and vergence BCEA were analyzed.
We found increased instability of the amblyopic eye during both eye viewing conditions. We also found increased instability in both controls and amblyopes under dichoptic viewing especially at low fellow eye contrasts. BCEA values increased from -0.12±0.07 at full contrast to -0.07±.12 at low contrast in the dichoptic environment in controls. Amblyopes responded more dramatically, with mean BCEA values increasing from 0.02±0.38 at full contrast to 0.1± 0.36 at low contrast for the fellow eye and from 0.32±0.29 at full contrast to 0.54±0.45 at low contrast for the amblyopic eye. Dichoptic viewing also affected eye alignment, with 4 of the 6 strabismic subjects experiencing pronounced increases in strabismus angle as compared with binocular viewing. Vergence BCEA increased from 1.93±.925 to 3.15±2.99 at 100% contrast in amblyopes, rising to 4.84±3.31 at low contrast. There was no such increase in controls.
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 2021 ARVO Annual Meeting abstract.
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