Age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness and visual disability in patients aged over 60 years in Europe and North America. It is the third leading cause of blindness, behind cataract and glaucoma, causing 8.7% of all legal blindness across the world. AMD is a disease with progressive, painless loss of central vision associated with ageing. AMD is widely classified into ‘dry’ and ‘wet’ types. ‘Dry’ AMD accounts for 10% of patients with visual loss and can be further classified into early, intermediate and late stages characterized by the presence of hyper and/or hypo-pigmentation with drusen within the macula. Studies have shown that drusen size is an important risk factor for predicting risk of advanced AMD. Large drusen are defined as those (within 2 standard disc diameters of the centre of the macula) with (shortest) diameter greater than or equal to that of an average normal retinal vein at the disc margin, considered to be approximately one-twelfth disc diameter or approximately 125 μm, when the average disc diameter is taken as 1500 μm; intermediate drusen are those with a disc diameter greater than or equal to one-half that of large drusen (63 μm). Drusen are extracellular deposits that accumulate between the basal lamina of the retinal pigment epithelium (RPE) and the inner collagenous layer of Bruch’s membrane in the human eye. They are typically associated with advancing age and are commonly observed in a variety of chorioretinal pathologies, including age-related macular degeneration. It is believed that local chronic inflammation through the activation of the alternative complement pathway with enucleation of drusen core. The consequent expansion affects the retinal pigment epithelium resulting in advancement from early to late stages. Late ‘dry’ AMD (geographical atrophy) and ‘wet’ AMD (choroidal neovascularization) are both classified as advanced AMD. Diagnosis and management of both these types of conditions differ.