Age-Related Macular Degeneration Is the Leading Cause of Blindness . . .

Commentary

Age-related macular degeneration (AMD) is the leading cause of blindness. . ." is a statement that can be found at the beginning of many peer-reviewed articles, presentations at scientific meetings, and grant applications in the specialty of ophthalmology. While it may not apply to worldwide blindness (cataract likely is the leading cause due to inadequate health services for cataract surgery in many parts of the world); to milder levels of vision impairment (refractive error in younger individuals, presbyopia with aging); to certain geographical regions (in which, for example, trachoma or onchocerciasis may be more prevalent); or to specific racial or ethnic categories (such as open-angle glaucoma among blacks in the United States), nevertheless, the statement highlights that AMD is a growing epidemic in many parts of the world.

In the April 2004 issue of the Archives of Ophthalmology, a theme issue on blindness, the Eye Diseases Prevalence Research Group (EDPRG) reports pooled findings from 7 population-based studies to provide more accurate data indicating that AMD is the leading cause of blindness in individuals older than 65 years in the United States.¹ The advanced stages of AMD, choroidal neovascularization, and geographic atrophy of the retinal pigment epithelium, which usually are associated with marked loss of central vision, are estimated to affect more than 1.75 million individuals in the United States.

Because the prevalence of the advanced stage of AMD is age-related, the authors indicate that based on the predicted aging of the US population, the prevalence of this condition is projected to increase to almost 3 million individuals in less than 20 years.¹

The EDPRG's results suggest that this number may be an underestimate of the problem. Approximately 20% of individuals who could have participated in the population-based studies failed to do so. Individuals with advanced-stage AMD are more likely to be nonparticipants in these studies, and thus undercounted because these individuals are less likely to have transportation to the study site and are more likely to be older with comorbid conditions preventing them from participating. Furthermore, the authors chose to assign the lower prevalence rates available from black participants compared with white participants to estimate the prevalence rates for Hispanics in the United States. However, recent data suggest that the prevalence of AMD in Hispanics may be higher than in blacks.² If the prevalence of advanced AMD is higher in Hispanics than in blacks, the estimates from the EDPRG may underestimate the prevalence of this condition in the United States, which may be compounded in the future because the proportion of Hispanics is expected to increase.

Even if the EDPRG data are not underestimated, the numbers are still large and of value to researchers and policy planners. For example, using information from the EDPRG, the Age-Related Eye Disease Study (AREDS) Group³ estimated that 8 million individuals in 2000 aged 55 years or older in the United States had a stage of AMD in 1 or both eyes (usually large drusen in at least 1 eye) considered to be at high risk for advanced AMD and for whom dietary supplementation such as the formulation used in AREDS should be considered.⁴

Based on natural history data from AREDS, 1.3 million of these individuals will develop advanced AMD within 5 years if no treatment is given to reduce their risk. If all of the individuals at risk received supplements such as those used in AREDS, more than 300 000 (95% confidence interval, 158 000-487 000) would avoid advanced AMD and any associated vision loss over the next 5 years. However, despite taking a dietary supplementation such as that used in AREDS, an estimated 1 million individuals still would develop the advanced stage of AMD. If these numbers double by 2020 and no other preventive treatments are found, at least 2 million individuals will develop the advanced stage of AMD in just 5 years from 2020 to 2025. Although treatments for the neovascular advanced stage of AMD in selected situations may reduce the risk of additional moderate or severe visual acuity loss beyond the presenting level to a treating ophthalmologist, and although other treatments for the neovascular stage under investigation may lead to even better outcomes, preventive strategies are the best chance for preserving excellent vision in individuals at risk for advanced AMD.

What do these numbers mean for the United States and countries with similar demographics? As the EDPRG indicates, "a determined effort to identify effective preventive strategies will be needed if we are to avoid a large increase in the numbers of persons" developing the advanced stages of AMD.¹ While some preventive strategies are under investigation, such as the Complications of Age-related Macular Degeneration Prevention Trial⁵ (sponsored by the National Eye Institute), it is unknown at this time how effective they will be.

With only 2 decades until the number of individuals with the advanced stage of AMD doubles, with timelines from AREDS suggesting that it takes 10 years from study design to proof of a preventive strategy in AMD,³ and given the profound effect that the advanced stage of AMD can have on vision-related quality of life,⁶ the EDPRG provides strong evidence for policy planners, sponsors (government, foundations, industries), investigators, the ophthalmic community, and the public to continue their efforts to reduce the risk of blindness from AMD. The result may be that some time in the future no one will be justified in starting an oral or written communication with the comment that "AMD is the leading cause of blindness . . ."

Funding/Support: Dr Bressler is the James P. Gills Professor of Ophthalmology. He was supported in part by the Michael B. Panitch Stop AMD Fund to prepare this article, but has no financial interest in the information presented.