It is well known that there are marked differences in the prevalence of certain ocular disorders among various ethnic groups. These differences probably reflect the unique genetic make-up of these ethnic groups coupled with a variety of environmental influences. Ethnic variations are particularly marked for the prevalence of myopia and hyperopia. While population based studies from the United States^1,2 and Australia^3,4 have reported a prevalence of myopia ranging from 15–26% in adults, the prevalence has been reported to be significantly higher in Singapore (35%).⁵ Asian countries in particular have also been experiencing a dramatic increase in the prevalence of myopia. For example, 82% of all ethnic Chinese Singapore military recruits screened between July 1996 and June 1997 were myopic.⁶

In this issue of the BJO (p 854), Yu and coworkers report that the incidence of exotropia is twice as common as esotropia in the strabismus clinic at the Hong Kong Eye Hospital, whereas studies based in Europe and North America have reported a much higher percentage of esotropes than exotropes. In addition, Yu and coworkers report that the ratio of exotropia/esotropia in Hong Kong has increased dramatically over the past decade. How can these differences be explained?

Firstly, the increased incidence …