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Sara Carroll, Guido Maiello, William Harrison, Peter Bex; Myopic Eyes See Better in a Crowd. Journal of Vision 2016;16(12):233. doi: 10.1167/16.12.233.
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© 2017 Association for Research in Vision and Ophthalmology.
The eyes of myopes are larger, both wider and especially longer, than the eyes of normally-sighted, emmetropic individuals. Even with best-corrected foveal vision, myopic peripheral vision is generally found to be worse than emmetropic peripheral vision. However, the functional vision of the periphery is limited not by acuity or contrast sensitivity but by visual crowding, the phenomenon by which visible targets become harder to identify in clutter. Because of the stretched myopic retina, objects projected onto the peripheral retinal surface of myopic eyes subtend the same retinal angle, but are spaced farther apart than on an emmetropic retina. We ask whether retinal angle or retinal spacing determines crowding. We measured letter acuity as well as radial and tangential crowding zones at 5, 10, and 15 degrees of eccentricity in emmetropic and best-corrected myopic observers. Consistent with previous results, peripheral letter acuity was worse in myopic than emmetropic subjects. We also confirmed the radial/tangential crowding asymmetry in both myopic and emmetropic observers: radial crowding zones were larger than tangential crowding zones by a factor of 2. Critically, our data show that both radial and tangential spatial interference zones in myopic eyes are smaller than in emmetropic eyes. This finding suggests that crowding zones may be determined by retinal spacing rather than by retinal angle. Although myopia is generally thought of as a visual impairment, and clearly hinders sensory aspects of visual function, our data suggest that the elongated retinal surface of myopic eyes may provide a functional benefit by extending the spacing within which peripheral targets are crowded. Our findings raise the possibility that at the supra-threshold object sizes and contrasts that dominate natural vision, interactions between central and peripheral vision might differ between myopes and emmetropes. These differences might play a neglected role in the development and progression of myopia.
Meeting abstract presented at VSS 2016
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