The incidence of myopia among Chinese students may be as high as 20 to 30% each year from first grade onward, according to a study published online July 5 in JAMA Ophthalmology
Myopia has reached epidemic levels among children in regions of East and Southeast Asia. High myopia is associated with myopic macular degeneration, glaucoma, and retinal detachment.
Sean K. Wang, from Sun Yat-sen University in Guangzhou, China, and colleagues performed an observational cohort study to examine the incidence of myopia and high myopia based on refraction without cycloplegia among 4,741 children from 19 primary schools and 22 junior high schools.
The researchers found that baseline mean spherical equivalent refraction (SER) was 0.31 diopters (D) among 1,975 students in grade 1 versus −1.6 D among 2,670 students in grade 7. In grade 1 students, the baseline prevalence of myopia was 12 percent, versus 67.4% in grade 7 students.
The incidence of myopia was 20% to 30% each year throughout both cohorts. The incidence of high myopia was initially less than 1% in the primary school cohort (grade 1: n = 2 of 1825; 0.1% [95% CI, 0.0%-0.3%]), but incidence exceeded 2% in the junior high school cohort (in grade 9: n = 48 of 2044; 2.3% [95% CI, 1.0%-3.7%]).
Myopia was defined as spherical equivalent refraction (SER) of −0.50 diopters (D) or less, as measured by subjective refraction without cycloplegia; high myopia was defined as an SER of −6.0 D or less.
Annual incidences were defined as the proportion of participants each year found to have myopia or high myopia who did not previously have the condition. Height, weight, axial length (AL), corneal radius of curvature (CRC), and AL/CRC ratio were examined to assess if these measures were associated with future myopia or high myopia.
Throughout both cohorts, the incidence of myopia was 20 to 30% each year. The incidence of high myopia was 0.1 percent in the primary school cohort and 2.3 percent in the junior high school cohort.
"The incidence of myopia among Chinese students based on refraction without cycloplegia is among the highest of any cultural or ethnic group," the authors write.