Accommodative lag at the onset of myopia in children

Abstract

Abstract: : Purpose: Defocus from accommodative lag is a putative risk factor for the onset and/or progression of myopia in children. Previously we have shown that while prevalent myopes have increased accommodative lag, greater amounts of lag were not associated with any increased risk of developing myopia (Mutti et al., ARVO, 2002). If increased lag accompanies but does not precede the onset of myopia, when does accommodative lag become different in children who develop myopia compared to those who remain emmetropic? Methods: The age of onset of myopia (–0.75 D or more myopic in each principal meridian) was identified in 102 children between the ages of 6 and 13 years participating in the Orinda Longitudinal Study of Myopia (OLSM) between 1997 and 2000. Accommodative lag to a 4.00 D stimulus measured annually before and after the onset of myopia was compared to age–matched predicted values of lag from a model derived from 47 OLSM children who were always emmetropic (between –0.25 D and +1.00 D). Lag measurements were included in the analysis only if the accommodative response was at least 1 D. Results: Mean accommodative lag for children who became myopic was not significantly different from those who remained emmetropic one year prior to myopia onset and at the year of myopia onset (mean differences = 0.053 D and –0.013 D; P = 0.50 and 0.84, respectively, one sample t–tests). Lag was significantly higher in children who became myopic compared to those who remained emmetropic by two years following the onset year by 0.33 D (P = 0.0049, one sample t–test). One year prior to myopia onset and at the year of myopia onset, statistical power to find an average difference in lag of 0.20 D between children who became myopic and those who remained emmetropic was 0.72 and 0.87, respectively. Conclusions: Increased accommodative lag occurs after onset as a later feature of myopia. Therefore, it is unlikely that accommodative lag will be a useful predictive factor for the onset of myopia.

Keywords: myopia • refractive error development • clinical (human) or epidemiologic studies: risk factor assessment