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T. T. Norton, L. Hyman, L. Dong, J. Gwiazda, COMET Study Group; Longitudinal Changes in Lens Thickness in Myopic Children Enrolled in the Correction of Myopia Evaluation Trial (COMET). Invest. Ophthalmol. Vis. Sci. 2008;49(13):2603.
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To describe longitudinal changes in lens thickness in myopic children and to investigate the association between changes in lens thickness and myopia progression.
469 ethnically diverse, 6-11 year old (median age, 9 years) children with -1.25 to -4.50 D of myopia were enrolled in COMET. Children remained in their original lens assignment (single vision [SVL] or progressive addition lens [PAL] with a +2 D add) for 5 years and were followed for an additional 3 years wearing PALs, SVLs, or contact lenses. Myopia by cycloplegic autorefraction (Nidek ARK 700A) and ocular component dimensions by A-scan ultrasound (Sonomed A2500) were measured annually. Analyses were based on right eyes of 445 subjects with 5-8 follow-up visits (90% completed an 8-year visit). Baseline lens thickness and myopia were compared across age groups using analysis of variance. Changes in lens thickness were tested using paired t-tests.
At baseline, the lens was thicker at younger ages (p= .0003), ranging from 3.49 mm for 6-7 year olds to 3.37 mm for 11 year olds. By comparison, the relationship between myopia and age was not monotonic, with the least myopia of -2.11 D in 8 year olds and the most myopia of -2.54 D in 9 year olds. During the first 2 years of follow-up, the period of most rapid progression, the lens thinned significantly in the youngest 3 age groups, by 0.06 mm (p<.0001), 0.05 mm (p<.0001), and 0.02 mm (p< 0.05) in 6-7, 8, and 9 year olds, respectively; lens changes in the older 2 groups were small and not significant. For the next 6 years, the lens became significantly thicker in all age groups, ranging from 0.04 mm (p = .004) in 6-7 year olds to 0.12 mm (<.0001) in 11 year olds. After 8 years of follow-up, when subjects were 14-19 years old, the lens was significantly thicker (p< .0001) than at baseline for the 3 oldest age groups. During this period of lens thickening, myopia progression began to slow. The relationship between lens changes and myopia progression also varied by age, with more lens thickening and less progression in the oldest 3 age groups. The relationship between longitudinal changes in lens thickness and in vitreous chamber depth was similar to that for myopia progression and lens changes. Overall, the pattern of lens changes appeared similar in the PAL and SVL groups.
Lens thickness does not appear to be related to the amount of myopia but varies with progression. These data suggest that the lens may thin while myopia is progressing rapidly and then thicken as progression begins to slow, with variation by age.
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