Age-related Macular Degeneration (AMD): A Review on its Epidemiology and Risk Factors

Abstract

Age-related Macular Degeneration (AMD) is a type of maculopathy that results in irreversible visual impairment among the aged population in developed countries. The early stages of AMD can be diagnosed by the presence of drusen beneath the retinal pigment epithelial (RPE) cells. The advanced stages of AMD are geographical atrophy (dry type) and neovascular AMD (wet type), which lead to progressive and severe vision loss. The advanced stage of dry AMD can be identified by extensive large drusen, detachment of the RPE layer and finally degeneration of photoreceptors leading to central vision loss. The late stage of wet AMD is diagnosed by the presence of Choroidal Neovascularization (CNV) identified by Optical Coherence Tomography (OCT) or retinal angiography. The principal of AMD management is to impede the progression of early AMD to advanced levels. Patients with CNV are treated with anti-VEGF (Vascular Endothelial Growth Factor) compounds to inhibit blood vessel growth and thereby reducing vision loss. Although preventive methods for dry AMD are under investigation, there are no proven effective treatments. A variety of environmental and genetic related risk factors are associated with increased incidence and progression of AMD. The genetic factors are found in the complement, angiogenic and lipid pathways. However, environmental factors, such as smoking and nutrition, are also major risk factors. Smoking is a modifiable environmental risk factor, which greatly increases the incidence and progress of AMD compared to non-smokers. There is growing evidence for the positive influence of a healthy diet containing high levels of anti-oxidant supplements. The reduction of serum lipids is another effective strategy for prevention AMD. Although no single preventive approach has been identified, knowing the high risk factors of AMD, along with modification of lifestyle is important for this multifactorial disease, especially in populations with higher genetic susceptibility. Though recent progress in early diagnosis of the disease has facilitated early and efficient intervention, further studies are required to gain more clarification of specific pathophysiology. In spite of decades of focused research on AMD, the pathogenesis of AMD is still not completely understood. Recently, numerous novel methods, including imaging techniques, new drug delivery routes, and therapeutic strategies, are improving the management of AMD. In this review, we discuss the current knowledge related to epidemiology and classifications of AMD.