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Howard S Ying, Vivian Xu, Robert B Geary, Boris I Gramatikov, David L Guyton, Kristina Irsch; Disconjugacy of eye alignment is greater with near fixation during binocular viewing in amblyopia. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3193. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To determine whether ocular disconjugacy in amblyopic subjects is dependent on viewing condition.
Binocular eye movements were recorded at 500 Hz using the EyeLink 1000 eye tracker (SR Research Ltd., Ontario, Canada). Twenty subjects (nine normal and eleven amblyopic; age: 8-45 years) were asked to fixate on a blue cross subtending 0.5° at a near distance of 57 cm or at a far distance of 4 m for 20-second epochs of binocular or monocular viewing. Disconjugacy of eye alignment was estimated by 1) the area of the 68% bivariate contour ellipse (BCEA) for the difference between right and left eye positions, 2) the percentage of fixation time within a 0.1°x 0.1° range, and 3) microsaccade characteristics. Mean ± standard error of the mean were calculate, log(BCEA) was used to normalize the distributions, and significance testing was performed with the Student’s t-test.
Normal subjects during binocular viewing showed a 68% BCEA of 0.75 deg2 ± 0.09 deg2 with near fixation and 0.81 deg2 ± 0.14 deg2 with far fixation (P=0.69) while subjects with amblyopia during binocular viewing showed a 68% BCEA of 5.60 deg2 ± 0.78 deg2 with near fixation and 3.08 deg2 ± 0.31 deg2 with far fixation (P=0.01). Mean percentage of conjugate fixation time for normal subjects was 99.5% ± 0.3% for near fixation and 99.6% ± 0.1 for far fixation (P=0.66), and for amblyopic subjects was 98.4% ± 0.2% for near fixation and 99.2% ± 0.1% for far fixation (P=0.02). Disconjugacy was associated with more microsaccades and more square wave jerks. Monocular viewing trials showed more disconjugacy than binocular trials for normal subjects but not for amblyopic subjects.
Disconjugacy increases with near fixation for amblyopic subjects during binocular viewing due to increased slow drift and microsaccades. Further research is required to determine which metrics have greater diagnostic utility in amblyopia.
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