Macular degeneration, also known as age-related macular degeneration (AMD or ARMD), is an eye disease that gradually damages the macula, the small central part of the retina responsible for sharp, detailed central vision. It mainly affects older adults and can make tasks like reading, driving, recognizing faces, or seeing fine details difficult. Wet-form AMD is when abnormal blood vessels grow under the macula and leak fluid or blood, damaging the retina and causing rapid loss of central vision. Dry-form AMD is when the macula gradually thins and small deposits called drusen build up, leading to a slow loss of central vision. Macular degeneration typically occurs in older people, and is caused by damage to the macula of the retina. Genetic factors and smoking may play a role. The condition is diagnosed through a complete eye exam. Severity is divided into early, intermediate, and late types. The late type is additionally divided into "dry" and "wet" forms, with the dry form making up 90% of cases. The difference between the two forms is categorized by the change in the macula. Those with dry-form AMD have drusen, cellular debris in their macula that gradually damages light-sensitive cells and leads to vision loss. In wet-form AMD, blood vessels grow under the macula, causing blood and fluid to leak into the retina. Exercising, eating well, and not smoking may reduce the risk of macular degeneration. No cure or treatment restores the vision already lost. In the wet form, anti–vascular endothelial growth factor injected into the eye or, less commonly, laser coagulation or photodynamic therapy may slow worsening. Dietary antioxidant vitamins, minerals, and carotenoids do not appear to affect the onset; however, dietary supplements may slow the progression in those who already have the disease. As of 2022, AMD affects more than 200 million people globally with the prevalence expected to increase to 300 million people by 2040 as the proportion of elderly persons in the population increases. It is more common in those of European or North American ancestry, and is about equally common in males and females. In 2013, it was the fourth most common cause of blindness, after cataracts, preterm birth, and glaucoma. It most commonly occurs in people over the age of fifty and in the United States is the most common cause of vision loss in this age group. About 0.4% of people between 50 and 60 have the disease, while it occurs in 0.7% of people 60 to 70, 2.3% of those 70 to 80, and nearly 12% of people over 80 years old.
Signs and symptoms
Early or intermediate AMD may be asymptomatic, or it may present with blurred or decreased vision in one or both eyes. This may manifest initially as difficulty with reading or driving (especially in poorly lit areas). Other symptoms of AMD include distortion of vision and blind spots (especially in and around the central visual field). Other signs and symptoms of macular degeneration include:
Distorted vision in the form of metamorphopsia, in which a grid of straight lines appears wavy and parts of the grid may appear blank: Patients often first notice this when looking at things like miniblinds in their home or telephone poles while driving. Central scotomas, shadows, or missing areas of vision Slow recovery of visual function after exposure to bright light (photostress test) Visual acuity drastically decreasing. (two levels or more), e.g.: 20/20 to 20/80 Blurred vision: Those with nonexudative (dry) macular degeneration may be asymptomatic or notice a gradual loss of central vision, whereas those with exudative (wet) macular degeneration often notice a rapid onset of vision loss (often caused by leakage and bleeding of abnormal blood vessels). Trouble discerning colors, specifically dark ones from dark ones and light ones from light ones A loss in contrast sensitivity Formed visual hallucinations and flashing lights have also been associated with severe visual loss secondary to wet AMD. Macular degeneration by itself will not lead to total blindness. For that matter, only a small number of people with visual impairment are blind. In almost all cases, some vision remains, mainly peripheral. Other complicating conditions may lead to such an acute condition (severe stroke or trauma, untreated glaucoma, etc.), 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 The pathogenesis of age-related macular degeneration (AMD) is intricately linked to gene-environment interactions. Key risk factors are age, race/ethnicity, smoking, and family history. Advanced age is the strongest predictor of AMD, particularly over 50.
Race and ethnicity
As illustrated by the Figure in this section, derived from data presented by the National Eye Institute of the United States, 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. "increasing intracellular concentrations of either tyrosine or L-DOPA both increase melanogenesis" or formation of the black pigment melanin. Thus there appears to be an association between reduced L-DOPA production and white skin. As suggested by the Figure and information in this section, reduced L-DOPA, resulting in white skin, appears to be associated with an increased risk of macular degeneration for white individuals over the age of 80.
… excerpt ends here. Continue reading the full article.
