Use of visual acuity to screen for significant refractive errors in adolescents: is it reliable?

To detect significant refractive error in a population-based random cluster sample of 12-year-old schoolchildren by using sensitivity and specificity of uncorrected visual acuity (VA).

The Sydney Myopia Study randomly selected 21 secondary schools stratified by socioeconomic status. All year 7 students (mean age, 12.7 years) were invited to participate. We tested VA monocularly, unaided at 2.44 m, using a retroilluminated logMAR chart. Cycloplegic autorefraction (induced with instillation of cyclopentolate hydrochloride, 1%) was used to define clinically significant refractive error as a spherical equivalent of -1.00 diopters (D) or less for myopia; at least +2.00 D for hyperopia; and -1.00 D or less cylinder power for astigmatism.

Data for both eyes were pooled for a total of 4497 observations. The sensitivity and specificity for all clinically significant refractive errors at the best VA cutoff level of 53 letters (6/6(-2)) were 72.2% and 93.3%, respectively. Myopia had the highest sensitivity and specificity of any of the refractive errors for detection using VA (97.8% and 97.1%, respectively, for a 45-letter VA cutoff [6/9.5]). The best VA cutoffs for hyperopia and astigmatism were 57 (6/6(+2)) and 55 (6/6) letters, respectively, with sensitivities of 69.2% and 77.4%, respectively, and specificities of 58.1% and 75.4%, respectively.

In this adolescent group, a VA cutoff of 6/9.5 or less detects myopic refractive error reliably. However, there is no reliable VA cutoff for clinically significant hyperopia or astigmatism. Improved VA screening methods are required to improve detection of these conditions. Even so, with the methods described herein, the prevalence of uncorrected VA may provide a reasonably accurate estimate of the prevalence of myopia.