Age-related Macular Degeneration (AMD)
The macula is a small central area of the retina. It is highly sensitive and produces detailed, colour images in the centre of the field of vision. Vision from the macula is important for driving, reading, recognition of faces and similar tasks.
Macular degeneration (MD) occurs when the macula is damaged. When its normal function is disrupted, vision is affecte. MD usually affects both eyes, but it may produce symptoms in one eye long before the other eye. If MD continues to its late stages, severe visual impairment can result. In most cases, visual loss is restricted to the central part of the vision. Peripheral vision usually remains in good condition.
There are several types of MD, but the most common is age-related macular degeneration (AMD). AMD usually occurs in people older than 50 years.
AMD is common. About 15 in every 100 people older than 50 have early signs of AMD. This includes disturbances of pigments in the retina and development of drusen, yellow deposits under the retina that may be a risk factor for AMD. Such initial changes in the macula are called "early AMD", but symptoms of visual disturbances are mild or not present. When complications of AMD threaten sight and cause substantial disturbances of vision, the condition is called "late AMD".
Types of late AMD
The two types of late AMD are "dry" and "wet".
1. Dry AMD develops slowly, usually over some years. As cells in the macula die in small patches, images fade and are unfocused. About four out of 10 people with late AMD have the dry type.
2. With wet AMD, new abnormal blood vessels grow from the choroid layer into the macula (see diagram, above). These vessels leak and bleed, leading to distorted vision and eventually to injured macula and retina. Scar tissue forms in and around the macula, and central vision is severely affected.