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Various combinations of risk factors and mechanisms may explain the complexity observed in AMD patients
Age related macular degeneration (AMD) is a “heterogeneous group of disorders” resulting in severe vision loss. The heterogeneity is a reflection of the variability of symptoms, clinical findings, and natural history observed in patients as well as the fact that AMD affects many cell types in the eye, including the neural retina, photoreceptors, retinal pigment epithelium (RPE), Bruch’s membrane, and the choriocapillaris. Clinically, “dry” or early AMD is characterised by large drusen and RPE pigmentary changes that can progress to an advanced stage, geographic atrophy. “Wet” or neovascular AMD, another manifestation of advanced disease, is characterised by choroidal neovascularisation (CNV). Clinical classification of early AMD is based on photographic assessment of drusen size and extent in the macula.1 These classification systems are also used by investigators interested in the analysis of genetic, epidemiological, and morphological features of AMD.
The pathological hallmark of early AMD is the accumulation of lipid and protein rich deposits (drusen and basal deposits) between the RPE cells and the choroid. The pathogenic mechanisms of deposit formation in AMD are still emerging, but the best data indicate involvement of lipid biochemistry, oxidative stress, dysregulated extracellular matrix molecules, and inflammation. Not surprisingly, diversity has also been observed in epidemiological associations between environmental and genetic risk factors for AMD, many of which vary among ethnicities. With this in mind, it follows, that various combinations of risk factors and mechanisms may explain the complexity observed in AMD patients, giving rise to a “heterogeneous group of disorders.” But, is our current classification system comprehensive enough to allow us to tease out the complex interrelations between genetics and environment?
HOW DO WE ASSESS THE CONTRIBUTION OF GENETICS VERSUS ENVIRONMENT?
One way is to identify environmental, genetic, and systemic health differences that are involved in the …