), but few macular degeneration patients experience total visual loss.The area of the macula constitutes only about 2.1% of the retina, and the remaining 97.9% (the peripheral field) remains unaffected by the disease. Even though the macula provides such a small fraction of the visual field, almost half of the visual cortex is devoted to processing macular information.In addition, people with dry macular degeneration often do not experience any symptoms but can experience gradual onset of blurry vision in one or both eyes. People with wet macular degeneration may experience acute onset of visual symptoms. Risk factors
Key risk factors are age, race/ethnicity, smoking, and family history. Advanced age is the strongest predictor of AMD, particularly over 50. Race/Ethnicity
As illustrated by the Figure in this section, derived from data presented by the National Eye Institute of the United States (https://www.nei.nih.gov/learn-about-eye-health/eye-health-data-and-statistics/age-related-macular-degeneration-amd-data-and-statistics/age-related-macular-degeneration-amd-tables), among those over 80 years of age, White individuals are more than 6-fold more likely to develop AMD than Black or Hispanic individuals. Thus, white background is a major risk factor for AMD. In Caucasian (White) skin, there is a specific group of polymorphic genes (with single nucleotide alterations) that encode for enzymes and transcription factors responsible for the early steps (including the first step, formation of L-DOPA from the amino acid tyrosine) of the melanin synthesis pathway. Many of these enzymes and transcription factors are reviewed by Markiewicz and Idowu. Also, as reviewed by Sturm et al.
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.