Amblyopia and subnormal visual acuity. Studies of prevalence, assessment and outcome

Abstract

Aims. The aims of this thesis were threefold. Firstly, we wanted to establish the distribution of visual acuity (VA) and the prevalence of amblyopia and other ocular disorders in two population-based samples of 12-13-year-old children, one that had been vision-screened at preschool age and the other that had not. Secondly, we aimed to describe the ability of stereo tests to detect amblyopia and strabismus in a screening situation, and thirdly, to evaluate long-term visual outcome of treatment for amblyopia in a well-controlled group.Materials & Methods. Papers I - IV report on two field studies performed in Sweden and Mexico. Just over 1,000 12-13-year-old children from each country were included. A full eye examination was performed and children with pathology were referred to an eye clinic. The Swedish population had been vision-screened at preschool age. In Paper V, 24 subjects were re-examined at a mean of 10.4 ± 1.9 years after cessation of the amblyopia treatment and the outcome of VA was evaluated.Results. In both the Swedish and the Mexican 12-13-year-olds, visual status was found to be good. With the exception of amblyopia and astigmatism, the overall results were surprisingly similar. The majority of subjects were found to have normal VA. Only one child had bilateral VA of =0.3. The prevalence of amblyopia (= 0.5) was 1.1% for Sweden and 2.5% for Mexico, which is similar to that in other vision-screened and nonvision-screened populations. Myopia (= -0.5 D) was common in both populations (45% in the Swedish and 36% in the Mexican). Ocular albinism was found to be up to 100 times more prevalent than previously assumed. In a substantial number of children with bilateral subnormal VA (44%), we did not have a causal diagnosis.None of the five stereo tests we studied qualify as a screening test for amblyopia or strabismus due to large numbers of both underreferrals and overreferrals. The results for both ocularly normal subjects and subjects with strabismus and/or amblyopia were very varied. We conclude that there is no way of separating a normal response from a pathological response. Regarding visual outcome after amblyopia treatment, VA was found to be stable in the amblyopic eye 10 years after cessation of treatment.