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G.W. Fulk, L.A. Cyert, J.K. Sawyer; Central Cornea Flattens Over 30-month Period in Myopic Children . Invest. Ophthalmol. Vis. Sci. 2003;44(13):797.
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Purpose: to determine if the curvature of the central cornea changes in myopic children over a 30-month period. It has been established that the central cornea flattens early in life and is stable in adulthood. Longitudinal studies of school children have given somewhat conflicting results. The Orinda Longitudinal Study (1996, OVS 73:552-7) of 387 children of all refractive errors followed for three years reported corneal flattening with no change in toricity. Horner et al. (2000,OVS 77:198-203) reported that 48 myopic children had no significant change in central corneal curvature over a five-year period. Methods: As part of a randomized clinical trial of the use of bifocals to slow myopia progression in children from six to 12 y/o and with near-point esophoria at baseline, central corneal curvature was measured with a Nidek ARK 900 (Marco, Inc; Jacksonville, FL). Measurements were made every six months. We report here on 68 children for whom we were able to obtain 3 measures at each of seven visits. We used the Fourier transform system (Thibos et al, 1997, OVS 74:367-75) to express central corneal power as M, J0 and J45 and examined changes from baseline to closeout. Results: Strong evidence of non-normality of the distribution in the change in corneal power was present, especially for children wearing bifocals (BF); so the Wilcoxon signed-rank test was used to assess median change. In both eyes of both treatment groups the spherical equivalent (M) of the central corneal power decreased significantly (p<0.008 for each group). In OD the median changes were -0.083 D in the BF and -0.075 D in the single vision (SV) group; the OS median changes were -0.085 D for BF and -0.12 D for SV. J0 and J45, which indicate astigmatism, showed little evidence of change in most groups; although J0 in SV decreased due to more flattening in the horizontal meridian than the vertical, p=0.001 OD, 0.177 OS. Conclusions: The cornea flattens in myopic children before puberty with little change in corneal astigmatism.
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