Optical Defocus Regulates Refractive Development in Primates via Local Retinal Mechanisms

Abstract

Purpose: : To determine whether the influence of optical defocus on ocular growth and refractive development is mediated by local retinal mechanisms in primates, we investigated the effects of optically imposed, nasal-field hyperopic defocus on the pattern of peripheral refractions in infant rhesus monkeys.

Methods: : Starting at 3 weeks of age, 8 infant monkeys were reared wearing -3 D spectacle lenses over one eye that produced relative hyperopic defocus in the nasal field, but allowed unrestricted vision in the temporal field (NF-3D). Control data were obtained from the non-treated fellow eyes of the NF-3D monkeys and from 7 normal monkeys. Refractive development was assessed by retinoscopy performed along the pupillary axis and at horizontal eccentricities of 15, 30 and 45 deg. Central axial dimensions and eye shape were assessed by A-scan ultrasonography and magnetic resonance imaging (MRI), respectively.

Results: : Relative hemi-field hyperopic defocus altered refractive development in a regionally selective manner. Compared to their fellow eyes, the NF-3D treated eyes exhibited relative myopic errors in the nasal field that were most obvious at the 15 (-1.29 ± 0.62 D) and 30 deg eccentricities (-1.20 ± 0.86D). Seven of the 8 NF-3D monkeys exhibited interocular differences refractive error in the nasal field that were outside the range of differences for normal monkeys. These alterations in the pattern of peripheral refractions in the NF-3D monkeys were associated with local, region-specific alterations in vitreous chamber depth in the treated hemi-retina.

Conclusions: : Like form deprivation, the effects of optical defocus in primates are dominated by local retinal mechanisms that integrate visual signals in a spatially restricted manner and exert their influence selectively on the subjacent sclera.

Keywords: emmetropization • refractive error development • myopia