Analysis of refractive state in 674 children aged 3 to 6 years old with subnormal vision

Objective To investigate the distribution of refractive state in children aged 3 to 6 years old with subnormal vision and to analyze the relationship between different refractive types and amblyopia. Methods This was a descriptive study of 674 children (1 348 eyes) aged 3 to 6 years old who had subnormal vision (3 years old≤20/40, 4 years old≤20/32, 5-6 years old≤ 20/25). Refraction and corrected visual acuity were detected after cycloplegia using 1% atropine ointment. The distribution of refractive errors in cases with and without amblyopia were analyzed. The incidence of anisometropia at different ages and the relationship between anisometropia and amblyopia were studied. The distribution of refractive errors and the incidence of amblyopia were compared by the chi-square test. Results The majority of the children were hyperopic, and myopia rarely occurred. With increasing age, the proportion of children with hyperopia decreased gradually while myopia increased, and the difference was statistically significant (χ2=99.7, P<0.001). There was a significant difference in the distribution of refraction between amblyopic and non-amblyopic eyes (χ2=20.1, P=0.01). The first three refractive causes of amblyopia were compound hyperopic astigmatism (59.4%), simple hyperopia astigmatism (17.8%), and mixed astigmatism (15.8%). No amblyopia occurred in the eyes with simple myopia. The incidence of amblyopia was higher when the spherical equivalent difference between the two eyes was or more than 1 diopter. There was a significant increase in the occurrence of amblyopia with increased anisometropia (χ2=62.9, P<0.001). Conclusion The majority of children 3 to 6 years old with subnormal vision have hyperopia. Hyperopia, astigmatism, and anisometropia are prone to cause amblyopia. Key words: Children; Subnormal vision; Refractive state; Anisometropia; Amblyopia