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P. Kang, P. Gifford, P. McNamara, J. Wu, S. Yeo, B. Vong, H. A. Swarbrick; Peripheral Refraction in East Asians and Caucasians. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3940.
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To investigate if there is a difference in peripheral refraction in young adults of East Asian versus Caucasian ethnicity.
Sixty eight subjects (35 East Asians and 33 Caucasians) aged between 18 and 37 years were enrolled. Non-cycloplegic central and peripheral refraction (Shin-Nippon NVision K-5001 autorefractor) were measured at 5º intervals to 35º in the nasal and temporal visual field along the horizontal meridian. Corneal topography (Medmont E300) was measured in the right eye. Conventional sphero-cylinder refraction was converted to vector components M (S+(C/2)) and J180 (-(C/2)cos2) where S is the sphere, C the cylinder and the axis. Vector components were used to calculate effective power along the horizontal meridian (M + J180). Subjects were subsequently categorised into three groups; hyperopes (plano to +3.25D), low myopes (< plano to -2.50D) and moderate myopes (< -2.50 to -5.25D). Mixed model ANOVA and 2-tailed paired Student’s t-tests were used to compare values between the two ethnic groups.
Peripheral refraction values in the hyperope and low myope groups showed no statistically significant difference (hyperopes p=0.312, low myopes p=0.166) between East Asian and Caucasian subjects. However, a significant difference was found between East Asians and Caucasians in the moderate myope group (p<0.05). Corneal eccentricity and tangential power values revealed nonsignificant differences in corneal profiles along the horizontal meridian between East Asian and Caucasian subjects (hyperopes p=0.45, low myopes p=0.42, and moderate myopes p=0.28).
The peripheral refraction profile was significantly different between East Asians and Caucasians in the moderate myope group. Additionally, corneal topography values were found to be similar in all subjects indicating that there is minimal effect of corneal shape on peripheral refraction differences found in moderate myopes between the two ethnic groups. Further investigation is required to determine if differences in peripheral refraction are due to differences in retinal shape or other ocular components such as the crystalline lens. Inherent differences in ocular biometry between ethnic groups may be relevant to understanding the high prevalence of myopia in East Asia as compared to other countries.
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