Health's Book

Definition

Age-related macular degeneration (AMD) is one of the most common causes of vision loss among adults over age 55 living in developed countries. It is caused by the breakdown of the macula, the central part of the retina located in the back of the eye. The macula allows people to see objects directly in front of them (called central vision), as well as fine visual details. People with AMD usually have blurred central vision, difficulty seeing details and colors, and they may notice distortion of straight lines.

Symptoms

AMD causes no pain. In some cases, AMD advances so slowly that affected individuals may not notice much change in their vision. In other cases, the disease progresses fast and may lead to a loss of vision in both eyes. One of the most common signs of early AMD is drusen, which is yellow deposits under the retina, most common in individuals over the age of 60. Drusen can be detected during a comprehensive dilated eye exam. Individuals with early AMD have several small drusen to a few medium-sized drusen. At this stage, there are no other symptoms and no vision loss. Individuals with intermediate AMD have many medium-sized drusen to one or more large drusen. The most common symptom at this stage is a blurred area in the central field of vision. Increased light may be necessary for reading and other tasks. Individuals with advanced AMD have drusen along with a degeneration of light-sensitive cells and supporting tissue in the central retinal area. A blurred spot in the central field of vision gets larger and darker over time. There is difficulty reading and recognizing objects from afar. As the AMD progresses, functional vision may be entirely lost in both eyes. AMD may also cause decreased color vision. Vision loss from dry AMD in only one eye may make it harder to notice changes in overall vision, as the other eye compensates.

While the majority of people with AMD maintain their peripheral vision, the severity of symptoms is dependent on the type of AMD. Wet AMD and advanced dry AMD are associated with the most symptoms. Wet AMD may cause straight lines to have a wavy appearance. The degree of change of visual acuity and other symptoms that can be seen by an eye exam increases over time. Individuals with dry AMD usually develop decreased visual acuity very slowly over a period of many years. Detectable changes are small from year to year, and central vision is partially retained. However, individuals with wet AMD usually have symptoms that precipitate quickly and have a greater risk of developing severe central vision loss in as little as a two-month period. Individuals with dry AMD may suddenly develop wet AMD without undergoing progressive stages of dry AMD.