The Effect of Ethnicity on Axial Length and Ocular Shape Before and After the Onset of Myopia

Abstract

Abstract: : Purpose: To investigate the behavior of ocular length and shape before onset, in the year of onset, and following the onset of myopia in children. Methods: Subjects were 482 myopic children age 6 to 14 years participating in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study between 1989 and 2002. Ethnicity was determined by parent survey (African–American, Asian–American, Caucasian, Hispanic). Refractive error was measured by cycloplegic autorefraction. Axial length (AL) was measured by A–scan ultrasonography. Ocular shape was measured by relative peripheral refraction (RPR), i.e., the difference in spherical equivalent refractive error between primary gaze and 30° in the nasal visual field. Measurements made annually from 5 years before to 3 years after the onset of myopia (–0.75D or more myopia in each principal meridian) were compared between ethnic groups. These values were adjusted for normal, age–matched change in refractive error, AL, and RPR based on a model derived from 446 CLEERE children who were always emmetropic (between –0.25 D and +1.00 D in each meridian). Results: Refractive error, AL, and RPR showed differences between ethnic groups as a function of time (year by ethnicity interactions significant in each model, P<0.0009). Refractive error was not different between ethnic groups before myopia onset, but Asian–American children showed more myopia at onset and faster progression. AL was longest in Hispanic children before onset, but Asian–American children showed the fastest growth in AL. Their AL was equal to Hispanics at onset and longer than African–American and Caucasian children following onset. RPR was not different between ethnic groups up to one year before onset. Asian–American children had the most prolate and African–American children the least prolate ocular shapes one year prior to onset and following onset. Conclusions: The development of refractive error, AL, and RPR varied as a function of ethnicity. Asian–American children tended to show the most myopia, the fastest growth and the most prolate shape. The similarity between ethnic groups several years prior to myopia onset suggests less ethnic variation for these components during emmetropia compared to after the onset of myopia.

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