Ocular Components Before and After the Onset of Myopia

Abstract

Abstract: : Purpose: To compare ocular component development prior to and following the onset of myopia with emmetropic development. Methods: The onset of myopia (-0.75D or more myopic in each principal meridian) was identified in 247 children between the ages of 6 and 13 years participating in the Orinda Longitudinal Study of Myopia (OLSM). Using growth curve model information derived from 194 OLSM children who were always emmetropic (between -0.25D and +1.00D), ocular component data before and after the onset of myopia were compared to their predicted values based on the age of the child. Slopes of the differences between the observed value (i.e., for a child who became myopic) and the expected value (i.e., from children who were always emmetropic) were obtained for the time before and after the onset of myopia. These slopes were compared to zero (i.e., no difference between growth of myopic and emmetropic children) and to each other (i.e., no difference in growth pattern before and after onset of myopia). Results: Prior to the onset of myopia the anterior and vitreous chambers enlarged and the crystalline lens flattened and thinned significantly faster in children who became myopic than in children who were always emmetropic (slopes = 0.009 mm/yr, 0.066 mm/yr, -0.102 D/yr, -0.006 mm/yr; P<0.001). After the onset of myopia the vitreous chamber continued to enlarge, but the crystalline lens changed direction to steepen (flatten less) and thicken (thin less) relative to emmetropic children (slopes = 0.152 mm/yr, 0.052 D/yr, 0.005 mm/yr; P<0.001). The faster rate of vitreous elongation and the change in sign to relative steepening and thickening after the onset of myopia were all significantly different compared to the slopes before the onset of myopia (P<0.001). Conclusions: Different rates of change in axial and lenticular components occur before the onset of myopia in children who become myopic compared to those who are always emmetropic. These differences may have value as longitudinal predictors of myopia onset. Development after the onset of myopia is not a simple extension of growth prior to myopia onset. The reversal to a relative crystalline lens steepening and thickening after the onset of myopia along with an acceleration of vitreous elongation suggests that the relative inability of the crystalline lens to sufficiently flatten and thin in the growing eye may play a role in the etiology of myopia.

Keywords: myopia • refractive error development • clinical (human) or epidemiologic studies: nat