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R.G. Bosworth, E.E. Birch; Binocular Function and Optoype-Grating Acuity Discrepancies in Amblyopic Children . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3183.
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Purpose: Amblyopic adults have greater deficits in optotype acuity than in grating acuity. The optotype-grating discrepancy is larger in strabismic than in anisometropic amblyopia. This may result from sparse or irregular neural sampling associated with abnormal binocular competition in strabismus but not anisometropia. However, since binocular function can be compromised in both disorders, it is possible that amblyopic patients with poor binocular function will have large optotype-grating acuity discrepancies regardless of etiology. Here we evaluate binocular status and the optotype-grating acuity discrepancy in a large prospective cohort of amblyopic children. Methods: Acuity and stereopsis were evaluated in 57 children (2.6-11 yrs of age) with amblyopia (≥3 lines) due to anisometropia (N=7), strabismus (N=33), or combined (N=17). Most patients were treated with occlusion, glasses, or surgery; alignment was within 8 pd at the time of testing. Optotype acuity, grating acuity, and stereoacuity were assessed on the same visit. In addition, 36 of the patients performed a monocular vernier acuity task with the amblyopic eye. Results: Overall, amblyopes had 2X worse optotype acuity than grating acuity; the mean optotype-grating discrepancy did not differ as a function of etiology (F=1.7; p=0.19). The optotype-grating acuity discrepancy was smaller for children with stereopsis (N=13; 0.05 logMAR) than for children with nil stereopsis (N=43; 0.33 logMAR); t=6.7; p<0.001. A strong association between stereoacuity and the optotype-grating acuity discrepancy was found even when the analysis was limited to a single etiology or to only moderate amblyopia (20/40 to 20/80). Moreover, the optotype-grating discrepancy was highly correlated with poorer performance on the vernier task (r=0.65; p<0.001). Amblyopic children with preserved stereopsis had vernier thresholds within 0.13 log unit of mean normal while those without stereopsis had an mean vernier deficit of 1.3 log units (t=1.8; p=0.04). Conclusions: Regardless of etiology, amblyopic children with nil stereopsis had large optotype-grating acuity discrepancies, consistent with undersampling/disarray of binocular cortical cells. The larger vernier deficit also found in amblyopic children who lacked stereopsis supports a link between impaired binocular function and neural undersampling/disarray.
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