The Role of Peripheral Vision in the Refractive–Error Development of Infant Monkeys (Macaca mulatta)

Abstract

Abstract: : Purpose: Emmetropization is a vision–dependent process that appears to be mediated primarily by local retinal mechanisms. Given the prominence of the fovea and central vision in primates, it seems likely that the emmetropization process in higher primates is dominated by local retinal mechanisms in the fovea and that peripheral mechanisms have little impact on overall eye growth. The purpose of this study was to examine the impact of peripheral vision on emmetropization in monkeys. Methods: Bilateral, peripheral form deprivation was produced in 12 infant monkeys by rearing them with diffuser lenses that had either 4 (n=6) or 8 mm (n=6) apertures centered on the pupils of each eye to allow approximately 20 or 40 degrees of unrestricted central vision, respectively. The rearing procedures were initiated at about 3 weeks of age and continued until the monkeys were about 4 months of age. At the end of the rearing period, an Argon laser was employed to ablate the macular area in one eye of 7 representative monkeys. Subsequently, all of the animals were allowed unrestricted vision. Refractive error along the eye’s pupillary axis, corneal curvature and the eye’s axial dimensions were measured every 2–3 weeks throughout the observation period by retinoscopy, keratometry, and A–scan ultrasonography, respectively. Results: By the end of the rearing period, 9 of the 12 diffuser–reared monkeys exhibited refractive errors that fell outside the range for normal monkeys. Eight of these monkeys had become relatively more myopic than normal while 1 monkey exhibited relative hyperopic errors. The refractive changes were symmetric in the two eyes of a given animal, axial in nature, and generally larger in the animals that wore the diffusers with the smaller central aperture. Following removal of the diffuser lenses, all of the treated monkeys exhibited recovery from the experimentally induced refractive errors. No interocular differences in the recovery process were observed in the 7 animals with monocular foveal lesions. Conclusions: The peripheral retina can contribute significantly to the normal emmetropization process and to refractive errors produced by abnormal visual experience. On the other hand, unrestricted central vision is not sufficient to ensure normal refractive development nor is it essential for vision–dependent emmetropizing responses. This pattern of results suggests that peripheral image quality could contribute to anomalous, vision–dependent refractive errors in children.

Keywords: emmetropization • myopia • refractive error development