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WR Davis, K Zadnik, D Mutti, T Raasch, N Friedman, G Mitchell; Corneal Shape in Children . Invest. Ophthalmol. Vis. Sci. 2002;43(13):175.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The shape of the corneal surface can be described in terms of a conic section by two values: corneal asphericity (Q) and apical radius of curvature. A relationship may exist between these shape parameters and other ocular dimensions, including refractive error, axial length, anterior chamber depth, and vitreous chamber depth. The purpose of the current study is to characterize these relationships in a large sample of children. Methods: Data used in this study were obtained from 683 subjects, ages 6 to 15, who participated in the Orinda Longitudinal Study of Myopia in 1991. Corneal topography measurements were taken using the Topographical Modeling System (TMS-1). Data generated by the TMS-1 were used to calculate Q and apical radius for each subject. These shape parameters were then compared with ocular dimension data. Results: The mean Q and apical radius for children in the study were -0.10 (±0.03) and 7.47 mm (± 0.24), respectively. Only 2 of the 683 children (0.29%) who participated in this study were found to have corneas that became steeper in the periphery, indicating an oblate shape (Q≷0). A relationship was found between Q and apical radius (r = 0.11, P = 0.006). A relationship was also found between Q and both axial length and anterior chamber depth (r = 0.12, p = 0.002 and r = 0.20, p < 0.0001, respectively). Apical radius was related to axial length, anterior chamber depth and vitreous chamber depth (r = 0.28, P < 0.0001; r = 0.11, P = 0.004 and r = 0.27, P < 0.0001, respectively). Neither Q, nor apical radius was related to refractive error. Conclusion: The current study agrees with previous studies, in finding the vast majority of corneas tend to flatten in the periphery, indicating a prolate shape (Q<0). We found that steeper corneas flatten more rapidly in the periphery, possibly to maintain smooth transition to the flatter sclera. Eyes with longer axial lengths and anterior chamber depths had steeper peripheral corneas. This relationship may reflect equatorial growth being outpaced by axial growth. While some previous studies have found Q and apical radius to be related to refractive error, the current study did not find this relationship.
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