The development of myopia in Hong Kong children between the ages of 7 and 12 years: a five-year longitudinal study.

The purpose of this work was to characterize the development of refractive error in Hong Kong children between the ages of 7 and 12 years. A non self-selected sample of 7-year old children was recruited and followed for 5 years, non-cycloplegic refractions being carried out annually. A life-table was used to determine myopia incidence and prevalence. The mean annual change in the spherical equivalent refraction (SER) was -0.32 D; 75 out of 83 subjects followed for 5 years became less hyperopic or more myopic, the maximum progression occurring between 9 and 11 years of age. The mean change in SER over the 5 years in children who were myopic at age 12 years was significantly greater than that in children who remained non-myopic. The incidence of myopia at age 7-8 years was 9% and at age 11-12 years was 18-20%. At age 7 years the prevalence of progressive myopia was 1.6% and 2.5% of subjects had anisometropia. Any treatment to prevent myopia should start by the age of 6 years and treatment to retard development should commence before age 9 years.