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Jasmine Junge, Deborah A Orel-Bixler; Effect of Contour Interaction on Visual Acuity in Cerebral Visual Impairment and Retinal Disorders. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2238.
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© ARVO (1962-2015); The Authors (2016-present)
Contour interaction has been defined as a reduction in visual acuity as affected by the distance of flankers from the central target. The underlying mechanism is unclear, but studies suggest that crowding occurs early in the visual cortex. Individuals with cerebral visual impairment (CVI) exhibit a reduction in visual acuity in the presence of increased contour interaction. The goal of this study was to examine the contour interaction effect in individuals with retinal disorders - achromatopsia and oculocutaneous albinism.
Binocular visual acuity was measured during a comprehensive vision examination for 43 subjects presenting with a diagnosis of CVI (ages 3-23; mean 9.13 years) and 25 subjects with achromatopsia or oculocutaneous albinism (ages 3-29 years; mean 7.6 years). Single Lea symbols with contour flanker bars at 50% and 100% spacing were presented in a two-alternative forced choice manner using the apple and the house as the test optotypes. Visual acuity thresholds were determined using the modified acuity card procedure by observation of the subject’s eye gaze, pointing, and/or naming of the optotype.
A Bland-Altman analysis compared the difference between the Lea visual acuity with 100% to 50% spacing versus the mean of the two measures. The average difference (bias) between the two acuity measures was -0.16 logMAR for the CVI (range 0.08 to -0.41) and -0.11 logMAR (range 0 to -0.3) for the retinal disorders groups, respectively, indicating worse acuity obtained with 50% spacing for both groups. However, the regression equations indicate a trend for a larger effect of contour interaction with worse mean acuity in the CVI group (y = -0.13x -0.08) but no trend in the retinal disorder group (y = 0.09x -0.18).
When comparing Lea visual acuity with 100% and 50% spacing between the central symbol and flanker bars, both the CVI and retinal disorder groups show worse acuity with increased contour interaction similar to normally sighted individuals. However the CVI group shows an increasing deleterious effect accompanying poorer visual acuity suggesting a greater cortical than retinal contribution to contour interaction.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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