Prevalence of Myopia in Schoolchildren and Risk Factors for Its Progression

Abstract

Myopia has a high and apparently increasing prevalence in Asia. In this ongoing cohort study, we first determined the age-specific prevalence of myopia and astigmatism in a single primary or elementary school in Singapore. We then asked if the progression of myopia was linear or quantal, and if it correlated with periods of intense near work imposed by varying scholastic requirements during the academic year. Examinations were performed every 2 months to measure the rate of progression of myopia and to quantify its risk factors. In this way, we hoped to ascertain the latency of any effect of long periods of near work on myopic eye growth. A crosssectional study of refraction was performed on 400 children from a single school, with approximately equal numbers in primary 1, 3, and 6. A cohort of 180 was then randomly selected, with about 60 in each age group. A 24-h near-work diary was administered at the start of the study (MIRF Visual Exposure Index) and repeated at each examination. A corrected Snellen visual acuity test, cycloplegic autorefraction, and ultrasound biometry were performed at each visit. The fit of the current spectacle prescriptions was also assessed. To date, the children have had 4 months of follow-up. Results show that the prevalence of myopia (>-0.5 D) was 25.8% at age 7, 32.8% at 9, and 51.5% at 12. The Prevalence of astigmatism was also high, being 32.2% at age 7, 25.0% at 9, and 24.2% at 12. The mean refraction of the children was +0.55, -0.50, and -1.25 D at ages 7, 9, and 12 respectively. An axial globe elongation and accompanying myopic shift was noted in the 7- and 9-year-old children even over 4 months. The increase was greater in the first 2 months, a period that coincided with school examinations. This was followed by relative stability of refraction and axial length during the school vacation that followed. In conclusion, the high prevalence of myopia in Asian schoolchildren may be causally related to long periods of intense near work. Further studies are needed to define the temporal relationship between the putative cause and the axial elongation. The potential for quantal myopic progression during narrow time intervals may offer future hope for drug treatment of limited duration or behavior modification likely to ensure treatment compliance.