Risk Factors for Age-related Macular Degeneration

Abstract

Age-related macular disease (ARMD) is a degenerative disease of the macula, most common over the age of 50 years.1 It is the leading cause of visual loss within western industrialised countries. [2][3][4] The number of blind registrations attributable to the disease increased by 30-40 % between 1950 and 1990 3 and the number of cases each year is continuing to rise 4-6 as these populations have an increasing longevity. Definition of Age-related Macular DiseaseThe international age-related maculopathy group has defined an international classification system for quantifying and defining the different subgroups of ARMD in an attempt to permit easier comparison of research findings between groups.1 Age-related maculopathy (ARM) is a disorder of the macular area most apparent after age 50 and is characterised by the following:• Areas of drusen which are external to the neuroretina and retinal pigment epithelium (RPE). They are soft and distinct or soft and indistinct. Hard drusen are not characteristic of ARM. Drusen are discrete white-yellow spots containing abnormal extracellular lipoprotein deposits that accumulate between the RPE basal lamina and the inner collagenous layer of Bruch's membrane. 7• Hyperpigmentation in the outer retina or choroid with drusen.• Hypopigmentation of the RPE with drusen.This early stage of the condition may not affect vision, but can predispose patients to visual loss (see Figure 1).Later stages of the condition are classified as 'wet' or 'dry' age-related macular degeneration (AMD). These forms of the disease can occur with or without the involvement of new blood vessel growth. If new vessels are not involved (dry AMD), clinical presentation is a sharply defined round or oval area of hypopigmentation where choroidal vessels are more visible than the surrounding area, with a diameter greater than 175 μm 1 (see Figure 2). This is also known as geographic atrophy (GA).The term 'wet AMD', also known as disciform AMD, exudative AMD or neovascular AMD refers to the development of choroidal neovascularisation (see Figure 3) and has numerous manifestations, including:• choroidal neovascularisation (CNV);• RPE detachment(s);• subretinal or sub-RPE neovascular membrane(s);• deposition of scarring, glial tissue or fibrin-like material within the epiretinal, intraretinal, subretinal or sub-RPE layers;• subretinal haemorrhages (without other retinal vascular cause); and• hard exudates (formed from lipid) associated with the above manifestations (without other retinal vascular cause).This article uses the terms ARM, AMD and ARMD as per the international classification system described. Physiology of Age-related Macular DiseaseThe RPE rests on Bruch's membrane and separates the neural retina from the choriocapillaris. The RPE phagocytoses the outer segment discs of the photoreceptors and is a point of metabolite and waste exchange, which is considered crucial to retinal function. 8 The initial signs of ARMD are variations within and below the RPE, seen as alterations in the pigmentation of the ...