Age-related macular degeneration (AMD) is a disease affecting vision. In this condition, central vision is lost with progressing age due to damage to the part of retina known as the macula. Central vision is required for routine daily living and is used to describe the vision from straight ahead. This vision is gradually or rapidly lost with onset of AMD depending on the type of AMD that the person suffers from.
The macula is a part of the retina at the back of the eye that is a highly pigmented yellow spot. The macula contains the fovea centralis. It is required for high acuity vision which contains a high concentration of cells known as cones, which are required to detect light. They relay visual stimuli to the brain. With onset of AMD, progressively vision is lost but is not accompanied by pain or discomfort. AMD is of two forms, wet and dry.
Wet AMD: This occurs when new blood vessels begin to form under the macula with fluid and blood leaking from them, leading to the macula being raised from its normal position. There is rapid loss of central vision with this condition.
Dry AMD: The dry form is also known as ‘Atrophic AMD.’ The cells on the macula which are sensitive to light gradually break down leading to loss of central vision. This is slowly progressive in comparison with wet AMD. With blurring of vision, there may be difficulty in recognizing people and the need for more light to perform tasks. With dry AMD, there might be single or multiple yellow deposits known as drusen, which are characteristic of this condition. Drusen are made of fat cells and cellular waste. This may affect one or both eyes at the same time. It occurs in three stages:
Early AMD: Where there are no symptoms and no loss of vision. There are few small or medium drusen present on examination.
Intermediate AMD: There is some blurring of central vision, with need for more light while performing tasks. On exam, multiple medium drusen or a large drusen are seen.
Advanced dry AMD: There are definite symptoms of blurred central vision with multiple large drusen on examination. Over time, the central vision is further compromised with difficulty with reading or in recognizing faces of people.
According to the Beaver Dam Eye Study, of all participants aged 75 and above, 30% have some degree of AMD. Twin studies indicate genetic factors playing an important role in the development of AMD.