Increased Caucasian Prevalence of Medium and Large Drusen, Focal Pigment Abnormalities, and Advanced Age-related Macular Degeneration

Abstract

Recent advances in effective therapies slow the progression of intermediate AMD to advanced AMD and decrease the risk for moderate vision loss associated with the development of choroidal neovascularization (CNV). However, epidemiological investigations remain important to identify possible risk factors for the development or progression of AMD, to recognize susceptible individuals and populations, to promote screening, education, and prevention tools, and to generate hypotheses for disease pathogenesis. For instance, the strongest and most consistent association between incident and prevalent AMD and a modifiable risk factor has been tobacco use. 2 It is theorized that hypoxia stimulates vascular endothelial growth factor (VEGF) production, which in turn upregulates retinal endothelial cell proliferation, which fosters the development of CNV. 3 Smoking may potentiate hypoxic retinal conditions, thus contributing to the pathogenesis and progression of AMD. Identifying patients with this modifiable risk factor and educating them about the potential benefits of tobacco cessation may have a significant long-term impact on lowering the incidence and progression of AMD. Many of the landmark epidemiological studies concentrating on AMD have employed a standardized approach to identify ‘cases’ of AMD. Case recognition has involved the use of high-quality stereoscopic color fundus photographs, obtained by certified photographers adhering to a protocol, which are then graded by trained and experienced readers with systematic application of standard definitions and reference photographs to generate levels of specific AMD features and levels of disease. As many studies have used similar means of generating their data, pooling of databases has been facilitated and some comparisons can be made between studies to partially overcome the limitation that only a few investigations have involved populations with heterogeneous ethnic backgrounds. While there are minor distinctions from one population-based study to the next in terms of the characterization of specific ocular features that comprise the early, intermediate, and advanced stages of AMD, the descriptions that follow are generally accepted, and the prevalence of each level of AMD has repeatedly been shown to be age-related. The label ‘early’ AMD requires that an eye has, as its most advanced feature, the presence of at least one medium-sized druse, with a linear dimension that is at least 64µm and up to 125µm (including 125µm in some studies) within 3,000µm (two standard disc diameters) of the foveal center.