Refractive errors in 3-6 year-old Chinese children: a very low prevalence of myopia?

Abstract

Purpose: To examine the prevalence of refractive errors in children aged 3-6 years in China.

Methods: Children were recruited for a trial of a home-based amblyopia screening kit in Guangzhou preschools, during which cycloplegic refractions were measured in both eyes of 2480 children. Cycloplegic refraction (from 3 to 4 drops of 1% cyclopentolate to ensure abolition of the light reflex) was measured by both autorefraction and retinoscopy. Refractive errors were defined as followed: myopia (at least -0.50 D in the worse eye), hyperopia (at least +2.00 D in the worse eye) and astigmatism (at least 1.50 D in the worse eye). Different definitions, as specified in the text, were also used to facilitate comparison with other studies.

Results: The mean spherical equivalent refractive error was at least +1.22 D for all ages and both genders. The prevalence of myopia for any definition at any age was at most 2.5%, and lower in most cases. In contrast, the prevalence of hyperopia was generally over 20%, and declined slightly with age. The prevalence of astigmatism was between 6% and 11%. There was very little change in refractive error with age over this age range.

Conclusions: Previous reports of less hyperopic mean spherical equivalent refractive error, and more myopia and less hyperopia in children of this age may be due to problems with achieving adequate cycloplegia in children with dark irises. Using up to 4 drops of 1% cyclopentolate may be necessary to accurately measure refractive error in paediatric studies of such children. Our results suggest that children from all ethnic groups may follow a similar pattern of early refractive development, with little myopia and a hyperopic mean spherical equivalent over +1.00 D up to the age of 5-6 years in most conditions.

Figure 1. Comparison of refractions measured by autorefraction and retinoscopy in right eyes.

Figure 2. Distributions of spherical equivalent refractive error by age.

The rectanglesrepresent the actual distributions of spherical equivalent refractive errors. The red lines represent normal distributions with the same means and standard deviations for each age. *In the group aged 5, the data of one outlier (female, −8,50 D in the right eyes) is not included.

Figure 3. Prevalence of refractive categories by age.

To facilitate comparison, definitions identical to those used in a comprehensive analysis of the distributions of refraction error from all the RESC studies are used in this figure. Myopia: −0.5 to +0.5 to +2.0 D.