A patch covering about 2 per cent of the retina commands half the visual cortex
The macula takes up only about 2.1 per cent of the retina, yet almost half of the brain's visual cortex handles what it sees. When age-related macular degeneration damages that tiny spot, reading and recognising faces grow hard, even though peripheral sight usually survives and total blindness is rare.
Age-related macular degeneration, or AMD, gradually harms the macula, the small central region of the retina that delivers sharp detail. It mostly affects people over fifty. Doctors grade it as early, intermediate or late, and the late stage comes in two forms. In the dry form, which makes up about 90 per cent of cases, debris called drusen builds up and slowly wears down light-sensing cells. In the wet form, abnormal blood vessels grow beneath the macula and leak blood and fluid, which can cause rapid loss of central vision.
Early disease may cause no symptoms at all. When signs do appear, they include blurring, trouble reading or driving in dim light, and blind spots near the centre of view. A telling clue is metamorphopsia: straight lines in a grid look wavy or partly blank, something people often first notice in window blinds or roadside telephone poles. Recovery after bright light can be slow, and dark shades can become hard to tell apart.
Age is the strongest predictor, alongside ethnicity, smoking and family history. Figures from the US National Eye Institute show that among people over 80, white individuals are more than six times as likely to develop AMD as Black or Hispanic individuals. Smoking tobacco raises the risk two to three times compared with never smoking, and may be the most important factor people can change. The 2013 ALIENOR study found no clear link with blood pressure itself, though a wider gap between systolic and diastolic readings was tied to late AMD.
As of 2022 more than 200 million people had AMD, a number expected to reach 300 million by 2040 as populations age. In 2013 it ranked fourth among causes of blindness, behind cataracts, preterm birth and glaucoma. Lost vision cannot be restored. For the wet form, anti-VEGF drugs injected into the eye, or less often laser treatment or photodynamic therapy, may slow decline, and supplements may slow progression in people who already have the disease.
Source: Macular degeneration
