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Alexandra Benavente-Perez, Ann Nour, David Troilo; Asymmetries in Peripheral Refraction Change with Emmetropization and Induced Eye Growth. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2731.
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Imposing full-field defocus on the retina of marmosets triggers compensatory changes in eye growth and refractive state that lead to asymmetries in the refraction of the peripheral retina. In this study we explore how these asymmetries change with age during untreated emmetropization and after induced changes in ocular growth to imposed peripheral defocus.
Nasal-temporal asymmetries in relative peripheral refraction were analyzed in untreated marmosets between 7 (N=16) and 19 (N=9) wks of age. We compared data from eyes treated with single vision contact lenses ¬-5D (SVN, N=14), +5D (SVP, N=18), bifocal contact lenses with a 3mm plano central zone with -5D or +5D in the periphery (3pl/-5, N=10; 3pl/+5, N=10), and bifocals with a 1.5mm plano central zone with +5D (1.5pl/+5, N=10). Refractions were measured at 7, 11, 15 and 19 wks of age using an IR photorefractor (MultiChannel System). Nasal-temporal asymmetries were calculated at 20 and 40 deg on the sagittal, tangential and spherical equivalent (SphEQ) image shells.
Results for each image shell were similar. We describe the changes in SphEQ here. During emmetropization in untreated marmosets (mean±se change in axial refraction: 4.19±0.45D), the mean asymmetry in peripheral refraction at 20 deg shifted significantly from relative hyperopia on the temporal retina at wk 7 to relative hyperopia on the nasal retina at wk 19. Marmosets treated with SVP or any bifocal contact lens showed a similar change in asymmetry. Marmosets treated with SVN experienced the greatest refractive asymmetry changes of all groups, also towards more nasal hyperopia, at both 20 and 40 deg.
Marmosets normally exhibit nasal-temporal asymmetries in near peripheral refraction that change with age toward relative nasal hyperopia. Similar shifts in asymmetry were observed in response to all experimental conditions, but were greatest when animals were treated with full-field negative defocus. These results suggest that the observed changes in the asymmetry of near peripheral refraction are related to increasing eye growth as seen during emmetropization. These changes increased significantly with compensation for imposed hyperopic defocus, possibly providing a stimulus for additional growth, but did not decrease with compensation for imposed myopic defocus, supporting the conclusion that the shift is related to increasing growth.
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