Valuing vision.

Abstract

Amblyopia affects up to 5% of all children and is the leading cause of monocular blindness in nonelderly adults.1 Because the effectiveness of treatment improves with early detection,2 preschool vision screening is widely endorsed.3,4 Unfortunately, the rate of vision screening is low in the primary care practice setting5,6 because of the difficulty of screening young children, lack of experience with the screening tests, and the high number of false positives associated with vision screening. Some communities have programs that offer vision screening to preschool children either by advocacy groups such as Prevent Blindness America and Lions clubs or local public health departments. Little is known about either the scope or effectiveness of community screening efforts for amblyopia. Because of the importance of early treatment for amblyopia and concerns about the low rate and questionable quality of preschool vision screening, the American Optometric Association recommends that all children have a complete eye examination at 6 months and then again at 3 years of age.7In this month’s Pediatrics, König and Barry8 present a cost-utility analysis of vision screening based on data collected in Germany. Their findings suggest that screening young children by orthoptists, trained specialists in the diagnosis and treatment of common types of visual impairment, has a reasonable cost per additional quality-adjusted life year compared with “usual care.”König and Barry’s results are based on statistical models that assume a certain loss of utility due to amblyopia. Amblyopia may adversely affect any activity that requires depth perception and may impact long-term educational attainment. However, there are no high-quality data to quantitatively assess the loss of utility.9 Instead, König and Barry based utility assessment on findings from adults with unilateral visual impairment. This may overstate the harm of amblyopia, because it does not consider compensatory mechanisms that individuals with amblyopia may develop; conversely, it may underestimate the harm caused by a lifetime of impairment leading to subtle declines in educational attainment. Assessing utilities is critical to ensuring robust cost-effectiveness models, but it is unclear how this could be done. Currently, there are no reliable means to assess utilities from young children; adults with amblyopia have never had normal vision and may not properly ascribe the harm of amblyopia, whereas adults with later onset of monocular vision loss have different experiences than those with amblyopia. There is a pressing need to develop a better understanding of the harm of amblyopia to ensure that screening efforts reflect the true potential benefit of early intervention.Finally, 2 factors must be considered before applying these results to the United States. First, the supply of orthoptists in the United States is insufficient to implement the program outlined in the study; other vision care providers would need to be included in screening efforts. Second, German children begin kindergarten at age 3, which eases the cost and logistic burden of early mass-screening outreach efforts. Despite these limitations, this study provides a useful and important framework for developing vision-screening policy.“Confusion caused by relative risks can be avoided by using absolute risks (such as one in 1000) or the number needed to treat or to be screened to save one life (the NNT, which is the reciprocal of the absolute risk reduction and is thus essentially the same representation as the absolute risk). However, health agencies typically inform the public in the form of relative risks. Health authorities tend not to encourage transparent representations and have themselves sometimes shown innumeracy, for example when funding proposals that report benefits in relative rather than absolute risks because the numbers look larger. For authorities that make decisions on allocation of resources the population impact number (the number of people in the population among whom one event will be prevented by an intervention) is a better means of putting risk into perspective.”Gigerenzer G, Edwards A. Simple tools for understanding risks. Br Med J. 2003;327:741–744Submitted by Student