Tendency for evolution of high myopia in 308 Chinese school children from Xi'an city

To observe the refractive status, especially the tendency for evolution of high myopia, in eyes of Chinese school children from Xi'an city.

The study was conducted in 11514 eyes of the 5757 students aged between 7-18 years in Xi 'an city primary and high schools. The inclusion criterion was > -6D of the spherical equivalent refraction. The object ophthalmic examinations were done, included non-cycloplegic objective refraction, visual acuity, intraocular pressure, fundus evaluation by ophthalmologists and nurses with professional training. Specially designed questionnaires were filled in and the data were statistically analyzed with SPSS10.0.

Of 11514 eyes, the detection rate was 81.4% (9376 eyes) for myopia and 5.3% (615 eyes) for high myopia. High myopia was found in 2.6% (300 eyes) of right eyes, 2.7% (315 eyes) in left eyes, and 2.4% (275 eyes) were in boys and 2.9% (340 eyes) in girls. Among 12 school grades, the detection rates of high myopia increased significantly with student age, with 0.9% in the 1st grade of primary school and 12.5% in the 3rd year of senior middle school. The average refractive error of spherical equivalent refraction was (-7.43 ± 1.29) D with 95% confidence interval (-7.54, -7.33). No significant differences were found between the right and left eyes or both genders. The distribution of myopic severity was lowest(-6D) in primary school students younger than 12 years, was higher (-8D) in junior middle school students older than 13 years, and highest (-13D) in senior middle school students.

A continuous growth was evident in the severity of high myopia throughout 12 years of primary and middle school except for the first year of primary school, with growth occurring in two transitional stages between the senior primary and junior middle school years, and between the junior and senior middle school years. The distribution of high myopia was lowest, at -6D, in primary school, increased to -8D in junior middle school, and progressed to -10D in senior middle school, indicating a high risk of development of pathologic myopia during the students' later lifespan. The adolescent period of 13 to 18 years of age in middle school is a critical period for the development of pathological myopia over -8D.