Longitudinal evidence of crystalline lens thinning in children.

PURPOSE: Most earlier studies indicated that the eye's crystalline lens grows continually throughout life, but cross-sectional results of crystalline lens thinning during childhood have been reported. The authors investigated crystalline lens thickness in childhood using cross-sectional and longitudinal data.
METHODS: The Orinda Longitudinal Study of Myopia is a community-based study of normal eye growth and myopia development in school-age children. During a 1-to 3-year period, A-scan ultrasonographic lens thickness measurements of 869 children 6 through 14 years of age were analyzed.
RESULTS: On average, between the ages of 6 and 10 years, the crystalline lens thins in its axial dimension by almost 0.2 mm. This thinning can be depicted by a cubic model. In this sample, the children with myopia had thinner crystalline lenses than the children with emmetropia of the same age.
CONCLUSIONS: This article provides the first longitudinal evidence that the crystalline lens thins during the period of coordinated ocular growth between the ages of 6 and 10 years. Further, it shows that lens thickness is associated with refractive error. Thinner crystalline lenses in children with myopia may result from one of two underlying mechanisms: Either the crystalline lens exhausts its ability to compensate for axial elongation after undergoing accelerated lens thinning before the onset of myopia, or the crystalline lens in the myopic eye may be thinner throughout childhood, during which it thins at a rate consistent with other refractive errors. If mechanical forces link eye growth to crystalline lens compensation, more complex, visually guided feedback loops may not be needed to explain the normal eye growth that results in emmetropization.