By: William C. Ou, BS, and Charles C. Wykoff, MD, PhD
Age-related macular degeneration (AMD) is a leading cause of visual impairment in the developed world.1 The pathophysiology of this disease is complex and involves both genetic and environmental risk factors; among the most important of these is age, particularly in light of shifting demographics in the United States. By 2030, one in five Americans will be over the age of 65,2 and it is predicted that the aging of the U.S. population will be accompanied by an increase in the disease burden of AMD.3–5
However, some data have suggested that AMD risk may actually be declining. For example, a comparison between the 1988-1994 National Health and Nutrition Examination Survey (NHANES) and the 2005-2008 NHANES revealed a decline in the prevalence of AMD in U.S. adults over the age of 40 years, from 9.4% to 6.5%.6 More recently, a meta-analysis of European AMD prevalence data revealed a declining prevalence of late AMD, both when data were stratified by study date (before or after 2006) and when data were stratified based on 10-year birth cohorts.7
Beyond observed declines in AMD prevalence, other studies have investigated AMD incidence over time. In the Beaver Dam Eye Study (BDES), patients born in later birth cohorts experienced a lower five-year incidence of early AMD than patients born in earlier birth cohorts.8
Perhaps the most implicated population cohort in discussions of AMD epidemiology is the Baby Boom Generation, which is rapidly aging into the risk years for AMD. In an effort to further explore generational trends in AMD risk with a focus on this demographic cohort, a study published at the end of 2017 analyzed combined data from both the BDES and the related Beaver Dam Offspring Study.9 Subjects were divided based on birth year into the Greatest Generation (1901-1924), the Silent Generation (1925-1945), the Baby Boom Generation (1946-1964), and Generation X (1965-1984); adjusted for age and gender, the five-year incidences of AMD in each generation were 8.8%, 3.0%, 1.0% and 0.3%, respectively. This decreasing trend in AMD incidence was preserved even after controlling for smoking, education, cholesterol and inflammatory markers, and each generation was approximately 60% less likely to develop AMD than the immediately preceding generation.
However, several key limitations to this study should be acknowledged. Although calculated incidences were adjusted for age, ideally each generation would have been studied over the same age range.10 The pooling of data from studies conducted over a decade apart allowed for substantial overlap in absolute age ranges between the Silent Generation and the Baby Boom Generation, but overlap among the other cohorts was limited. Additionally, it should be noted that even the oldest members of Generation X were still younger than 45 years old at the time of examination, and the majority of these subjects would not generally be considered to be at risk for AMD.
If taken to be fact, declining risk for AMD parallels observed declines in other chronic diseases including cardiovascular disease11 and dementia.12 The forces driving these trends may ultimately be impossible to elucidate, but may include factors such as diet, improvements in medical care or yet undetermined period effects. Furthermore, there may be some doubt about whether these trends will last. Obesity, an established risk factor for AMD, continues to trend upward and may have long-term effects on disease patterns that have not yet been uncovered. Indeed, in the realm of cardiovascular disease, there are fears that progress made over the last few decades has slowed or even begun to reverse.13,14
Ultimately, although risk could be on the decline, the absolute burden of AMD is still likely to increase as populations continue to age.7 It also remains unclear whether the trends observed in the Western world apply to the developing world, where populations are also rapidly aging.5 Therefore, additional work is needed before the present findings can be interpreted in a global context.
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Ford ES, Roger VL, Dunlay SM, Go AS, Rosamond WD. Challenges of ascertaining national trends in the incidence of coronary heart disease in the United States. J Am Heart Assoc. 2014;3(6):e001097.
Satizabal C, Beiser AS, Seshadri S. Incidence of Dementia over Three Decades in the Framingham Heart Study. N Engl J Med. 2016;375(1):93-94.
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About our author(s):
William Ou is a first-year medical student at the University of Texas Southwestern Medical School in Dallas. He previously completed a one-year research fellowship at the Retina Consultants of Houston in Houston, where he studied age-related macular degeneration and retinal vascular diseases.
Charles C. Wykoff, MD, PhD, is Director of Research, Retina Consultants of Houston and Deputy Ophthalmology Chair, Blanton Eye Institute, Houston Methodist Hospital.