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Eileen E Birch, Krista R Kelly, Reed Jost, Angie De La Cruz; The Role of Interocular Suppression in the Etiology of Amblyopia and its Response to Treatment. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3826.
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Recent psychophysical and animal model data have given rise to the hypothesis that amblyopia develops as a result of interocular suppression (IOS). This hypothesis is indirectly supported by reports that visual acuity and binocular vision can be improved with contrast-balanced binocular therapy designed to reduce IOS. To further test the hypothesis that IOS causes amblyopia, we determined whether (1) IOS precedes the development of amblyopia, (2) children who have persistent IOS despite successful treatment are at risk for recurrence of amblyopia, and (3) IOS is reduced by monocular and binocular amblyopia treatments.
70 children (4-12 y) with anisometropia, esotropia, or both (alignment <4pd on day of testing) and 20 age-similar controls were tested on 4±2 visits over 16±9 months. At each visit, visual acuity was tested with ATS-HOTV or e-ETDRS, and severity of IOS was quantified with a dichoptic motion coherence task (Mansouri et al Vis Res 2008) or a dichoptic eye chart (Birch et al IOVS 2016) and expressed as the contrast ratio (CR) at which IOS was alleviated.
Of 46 children who were nonamblyopic at their initial visit, 23 developed amblyopia during follow-up. Mean (±SE) CR was elevated relative to controls prior to the onset of amblyopia (3.95±0.60 vs 0.97±0.06; t41=4.61;p<0.0001) and compared to the 23 children who remained nonamblyopic throughout follow-up (1.22±0.08; t44=4.51; p<0.0001). Among the children who developed amblyopia were 8 children with no prior history of amblyopia (initial visit CR=4.38±1.17) and 15 with recurrent amblyopia (initial visit CR=3.80±1.50). 42 amblyopic children recovered normal visual acuity with treatment. While amblyopic, CR was 3.54±0.41, but improved to 2.73±0.41 following recovery (t41=2.10;p=0.042). Post-recovery CR for children who received binocular treatment (n=20; contrast-balanced iPad games or dichoptic movies) was 1.95±0.52 and CR for children who were treated with patching was 3.54±0.60 (n=21; t39=1.99;p=0.053).
IOS is present prior to the onset of amblyopia and diminishes when amblyopia resolves with treatment. IOS poses a risk for recurrent amblyopia if it persists when visual acuity recovers. These results provide additional support for the hypothesis that IOS plays a key role in the etiology of amblyopia and that treatments designed to reduce IOS can improve visual acuity and binocular vision.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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