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L.–F. Hung, Y. Qiao–Grider, C.–S. Kee, R. Ramamirtham, D.K. Coats, E.L. Smith, III; Contributions of the Fovea and Peripheral Retina to the Emmetropization Process in Monkeys . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2281.
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Purpose: Because of the prominence of central vision, it has been assumed that foveal mechanisms play an important role in the emmetropization process. Monkeys with foveal ablations, however, recover from form–deprivation myopia, suggesting that the fovea is not essential for emmetropization. The purpose of this study was to explore the contributions of the fovea and the peripheral retina to emmetropization. Methods: Photocoagulation using a frequency–doubled Nd–YAG or argon laser was employed to ablate the central 4–6 degrees of retina (n = 3) or the mid– to far–periphery (n = 5) in one eye of infant rhesus monkeys, at 3 weeks of age. Peripheral ablations extended from approximately 3 disc diameters from the fovea to the ora serrata. Fellow untreated eyes were followed as controls. The refractive status, corneal curvature and axial dimension of each eye were measured every 2–3 weeks for 5 months. Results: Foveal ablations had no apparent effect on emmetropization. As in normal monkeys, no systematic interocular differences in refractive error or axial dimension were observed. Peripheral ablations were associated with a complex series of alterations. Two weeks after the peripheral ablation, treated eyes, in comparison to their fellow control eyes, were consistently more hyperopic (+3.61 ± 1.77 D) and had shorter vitreous chambers (–0.88 ± 0.37 mm), thicker crystalline lenses (+0.26 ± 0.06 mm), and shallower anterior chambers (–0.26 ± 0.09 mm). Although some of these alterations persisted over time and were likely a direct consequence of the laser procedures, by 5 months of age the average degree of anisometropia had decreased to +1.59 ± 1.27 D, suggesting that some degree of vision–dependent emmetropization was still possible. Conclusions: Though an intact fovea is clearly not essential for emmetropization, peripheral retinal ablation, such as that employed to treat retinopathy of prematurity, can significantly alter refractive development.
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