Is Retinal Shape different in Asians and Caucasians? Estimation from Peripheral Refraction and Peripheral Eye Length Methods

Abstract

Purpose: Race appears to be associated with myopiogenesis, with East Asians showing high myopia prevalence. Considering structural variations in the eye, it is possible that retinal shapes are different between races. The purpose of this study was to quantify and compare retinal shapes between racial groups using peripheral refraction (PR) and peripheral eye lengths (PEL).

Methods: A Shin-Nippon SRW5000 autorefractor and a Haag-Streit Lenstar LS900 biometer measured PR and PEL, respectively, along horizontal (H) and vertical (V) fields out to ±35° in 5° steps in 29 Caucasian (CA), 16 South Asian (SA) and 23 East Asian (EA) young adults (spherical equivalent range +0.75D to −5.00D in all groups). Retinal vertex curvature R_v and asphericity Q were determined from two methods: a) PR (Dunne): The Gullstrand-Emsley eye was modified according to participant’s intraocular lengths and anterior cornea curvature. Ray-tracing was performed at each angle through the stop, altering cornea asphericity until peripheral astigmatism matched experimental measurements. Retinal curvature and hence retinal co-ordinate intersection with the chief ray were altered until sagittal refraction matched its measurement. b) PEL: Ray-tracing was performed at each angle through the anterior corneal centre of curvature of the Gullstrand-Emsley eye. Ignoring lens refraction, retinal co-ordinates relative to the fovea were determined from PEL and trigonometry. From sets of retinal co-ordinates, conic retinal shapes were fitted in terms of R_v and Q. Repeated-measures ANOVA were conducted on R_v and Q, and post hoc t-tests with Bonferroni correction were used to compare races.

Results: In all racial groups both methods showed greater R_v for the horizontal than for the vertical meridian and greater R_v for myopes than emmetropes. R_v was greater in EA than in CA (P=0.02), with R_v for SA being intermediate and not significantly different from CA and EA. The PEL method provided larger R_v than the PR method: PEL: EA vs CA 87±13 vs 83±11 m^-1 (H), 79±13 vs 72±14 m^-1 (V); PR: EA vs CA 79±10 vs 67±10 m^-1 (H), 71±17 vs 66±12 m^-1 (V). Q did not vary significantly with race.

Conclusions: Estimates of R_v, but not of Q, varied significantly with race. The greater R_v found in EA than in CA and the comparatively high prevalence rate of myopia in many Asian countries may be related.

Keywords: 605 myopia • 688 retina