Human eye cross-sectional view The pathogenesis of age-related<unk>  is not well known, although some theories have been put forward, including oxidative stress, mitochondrial dysfunction, and inflammatory processes. The imbalance between the production of damaged cellular components and degradation leads to the accumulation of harmful products, for example, intracellular lipofuscin and extracellular drusen. Incipient atrophy is demarcated by areas of retinal pigment epithelium (RPE) thinning or depigmentation that precede geographic atrophy in the early stages of AMD. In advanced stages of AMD, atrophy of the RPE (geographic atrophy) and/or development of new blood vessels (neovascularization) result in the death of photoreceptors and central vision loss. In the dry (nonexudative) form, cellular debris called drusen accumulates between the retina and the choroid, causing atrophy and scarring to the retina. In the wet (exudative) form, which is more severe, blood vessels grow up from the choroid (neovascularization) behind the retina which can leak exudate and fluid and also cause hemorrhaging. Early work demonstrated a family of immune mediators was plentiful in drusen. Complement factor H (CFH) is an important inhibitor of this inflammatory cascade, and a disease-associated polymorphism in the CFH gene strongly associates with AMD. Thus an AMD pathophysiological model of chronic low grade complement activation and inflammation in the macula has been advanced. Lending credibility to this has been the discovery of disease-associated genetic polymorphisms in other elements of the complement cascade including complement component 3 (C3). A powerful predictor of AMD is found on chromosome 10q26 at LOC 387715. An insertion/deletion polymorphism at this site reduces expression of the ARMS2 gene though destabilization of its mRNA through deletion of the polyadenylation signal. ARMS2 protein may localize to the mitochondria and participate in energy metabolism, though much remains to be discovered about its function. Other gene markers of progression risk includes tissue inhibitor of metalloproteinase 3 (TIMP3), suggesting a role for extracellular matrix metabolism in AMD progression. Variations in cholesterol metabolising genes such as the hepatic lipase, cholesterol ester transferase, lipoprotein lipase and the ATP-binding cassette A1 correlate with disease progression. The early stigmata of disease, drusen, are rich in cholesterol, offering face validity to the results of genome-wide association studies. Stages In AMD there is a progressive accumulation of characteristic yellow deposits, called drusen (buildup of extracellular proteins and lipids), in the macula (a part of the retina), between the retinal pigment epithelium and the underlying choroid. This accumulation is believed to damage the retina over time. Amyloid beta, which builds up in Alzheimer's disease brains, is one of the proteins that accumulate in AMD, which is a reason why AMD is sometimes called "Alzheimer's of the eye" or "Alzheimer's of the retina". AMD can be divided into 3 stages: early, intermediate, and late, based partially on the extent (size and number) of drusen. AMD-like pathology begins with small yellow deposits (drusen) in the macula, between the retinal pigment epithelium and the underlying choroid. Most people with these early changes (referred to as age-related maculopathy) still have good vision. People with drusen may or may not develop AMD. In fact, the majority of people over age 60 have drusen with no adverse effects. The risk of developing symptoms is higher when the drusen are large and numerous, and associated with the disturbance in the pigmented cell layer under the macula. Large and soft drusen are thought to be related to elevated cholesterol deposits. Early AMD Early AMD is diagnosed based on the presence of medium-sized drusen, about the width of an average human hair. Early AMD is usually asymptomatic. Intermediate AMD Intermediate AMD is diagnosed by large drusen and/or any retinal pigment abnormalities. Intermediate AMD may cause some vision loss, but, like early AMD, it is usually asymptomatic. Recently, subgroups of intermediate AMD have been identified, which have a very high risk of progression toward late AMD. This subgroup (depending on the precise definitions) is termed nascent GA and/or iRORA (incomplete retinal pigment epithelium and outer retinal atrophy). These 'high-risk' subgroups of intermediate AMD can be used to inform patients of theirs prognosis. In addition, these can be applied in clinical trials as endpoints. Late AMD In late AMD, enough retinal damage occurs that, in addition to drusen, people will also begin to experience symptomatic central vision loss. The damage can either be the development of atrophy or the onset of neovascular disease. Late AMD is further divided into two subtypes based on the types of damage: Geographic atrophy and Wet AMD (also called Neovascular AMD). Dry AMD Dry AMD (also called nonexudative AMD) is a broad designation, encompassing all forms of AMD that are not neovascular (wet AMD). This includes early and intermediate forms of AMD, as well as the advanced form of dry AMD known as geographic atrophy. Dry AMD patients tend to have minimal symptoms in the earlier stages; visual function loss occurs more often if the condition advances to geographic atrophy. Dry AMD accounts for 80–90% of cases and tends to progress slowly. In 10–20% of people, dry AMD progresses to the wet type. Geographic atrophy Geographic atrophy (also called atrophic AMD) is an advanced form of AMD in which progressive and irreversible loss of retinal cells leads to a loss of visual function. There are multiple layers that make up the retina, and in geographic atrophy, there are three specific layers that undergo atrophy: the choriocapillaris, retinal pigment epithelium, and the overlying photoreceptors. The three layers that undergo atrophy in geographic atrophy are all adjacent to each other. The photoreceptors are the most superficial and they are the cells that are responsible for converting energy from the light from the outside world, into an electrical signal to be sent to the brain. There are several functions of the retinal pigment epithelium. One of the main functions of the retinal pigment epithelium is to minimize oxidative stress. It does so by absorbing light, and thus preventing it from getting to the underlying layers. The layers underlying the retinal pigment epithelium are very vascularlized so they have very high oxygen tension. Thus, if light was to get to those layers, many free radicals would form and cause damage to nearby tissues. The deepest layer that undergoes atrophy in geographic atrophy is called the choriocappilaris. It is a capillary network that provides nutrients to the retinal pigment epithelium. The pathophysiology of geographic atrophy is still uncertain. Some studies questioned whether it was due to a deficient retinal pigment epithelium, leading to increased oxidative stress. Other studies have looked for inflammatory causes of damage. Thus far, the medical community is still not certain. Recent studies have begun to look at each layer individually. They found that decrease blood flow in the choriocapillaris precedes atrophy of the retinal pigment epithelium and the overlying photoreceptors. Since the choriocapillaris is a vascular layer, this may be used as an argument for why geographic atrophy could be a disease due to decreased blood flow. Wet AMD Neovascular or exudative AMD, the "wet" form of advanced AMD, causes vision loss due to abnormal blood vessel growth (choroidal neovascularization) in the choriocapillaris, through Bruch's membrane. It is usually, but not always, preceded by the dry form of AMD. The proliferation of abnormal blood vessels in the retina is stimulated by vascular endothelial growth factor (VEGF). Because these blood vessels are abnormal, these are also more fragile than typical blood vessels, which ultimately leads to blood and protein leakage below the macula. Bleeding, leaking, and scarring from these blood vessels eventually cause irreversible damage to the photoreceptors and rapid vision loss if left untreated. Oxidative stress Age-related accumulation of low-molecular-weight, phototoxic, pro-oxidant melanin oligomers within lysosomes in the retinal pigment epithelium (RPE) may be partly responsible for decreasing the digestive rate of photoreceptor outer rod segments (POS) by the RPE – autophagy. A decrease in the digestive rate of POS has been shown to be associated with lipofuscin formation – a classic sign associated with AMD. The role of retinal oxidative stress in the cause of AMD by resulting in further inflammation of the macula is suggested by the enhanced rate of disease in smokers and those exposed to UV irradiation. Mitochondrial dysfunction may play a role. Evidence was recently reviewed that damage to mitochondrial DNA may be an essential element of AMD pathogenesis and that overproduction of reactive oxygen species may play a role in this process.
Macular degeneration
Optic disc drusen
Macular scarring
Retinal degeneration 
Retinal vasculitis
Macular corneal dystrophy
Autoimmune optic neuropathy
Corneal neovascularization