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L. Jiang, K. Totonelly, X. Zhou, F. Lu, D. Troilo; Eye Shape in Chinese School Children Measured by MRI - The Wenzhou Eye Shape Study. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3144.
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Different eye shapes are associated with differences in refractive error, but the nature of the relationship between eye shape and the development of myopia, in particular, is unclear. We are conducting a longitudinal study of eye shape in Chinese school children, a population known to develop myopia in a large percentage of subjects. Baseline data from the initial measurements are presented here.
To date, we have recruited 35 children (mean age 11.6, range 9-13 yrs) from primary schools in Wenzhou, China. Subjects were categorized as emmetropic (n=21; spherical equivalent refractions between +0.75 and -0.25 D; mean±SD, +0.16±0.34 D) or low myopes (n=13; refractions <-0.25 D; range -0.5 to -2 D; -0.89±0.66 D). Only the right eyes were used. Axial refractive state was measured by cycloplegic retinoscopy. Axial eye length and eye shape were measured using MRI slices through the center of the eye in the transverse (horizontal) plane. The anterior-posterior (AP) axis was determined from the apex of the cornea to the inner surface of the retina using points on the apices of the anterior and posterior lens surfaces for alignment. The equatorial diameter (EQ) of the eye was taken as the distance from retina to retina of a line orthogonal to the AP axis at its midpoint. The ratio of EQ to the depth of the vitreous chamber (VC) measured along the AP axis was used as a simple measure of eye shape.
VC and EQ were not significantly different between emmetropes and myopes (mean±SD; VC 16.42±0.90 vs 16.54±0.68 mm, p=0.68; EQ 16.18±0.82 vs 15.97±0.47 mm, p=0.41). The ratio of EQ to VC was, however, significantly greater in emmetropes compared to myopes (0.986±0.026 vs 0.967±0.016, p=0.03) indicating that the eyes of emmetropes were more symmetrical than the eyes of myopes, which were longer on the AP axis relative to EQ width.
Chinese school children show a range of overall eye shapes, however we detected significant differences between emmetropes and low myopes even before axial VC depth differences were significant. Compared to emmetropes, the eyes of children with low myopia were longer-than-wide, consistent with other reports using MRI in adult human subjects, and in children measured by optical low coherence reflectometry. Because of the range of eye shape found in emmetropes, and the expectation that many will develop myopia, we should be able to determine whether eye shape is a predictor of the development of myopia.
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