Cross-sectional sample of peripheral refraction in four meridians in myopes and emmetropes

The study of peripheral refractive error is of growing interest as degradation of the retinal image quality in the periphery is known to affect central refractive error development and ocular shape in animal models. The purpose of this study was to measure peripheral refraction across the horizontal, vertical, and two oblique meridians in a group of myopic and emmetropic adults and to investigate retinal asymmetry in the human retina.

Thirty-one myopes (spherical equivalent between -2.00 and -9.62 D) and 20 emmetropes (spherical equivalent between -0.50 and +0.50 D) with astigmatism less than -0.75 D, participated in the project. Noncycloplegic peripheral refraction measurements were captured with an autorefractor (NVision K-5001; Shin-Nippon, Tokyo, Japan) at the fovea and up to 30° eccentricity in the horizontal, vertical, and two oblique meridians in 10° steps. RPR was calculated by subtracting the foveal spherical equivalent refraction from that obtained at each eccentric location.

Along all measured meridians, myopic eyes showed a relative hyperopic shift in the periphery, with the superior-temporal portion of the retina exhibiting the smallest shift. Emmetropic eyes, however, exhibited a relatively consistent refractive profile across all meridians and eccentricities, confirming a spherical retinal shape for this group. In addition, off-axis astigmatism increased with eccentricity in all meridians.

These results suggest that the myopic eye tends toward an ellipsoid shape, rather than the globular shape of an emmetropic eye.