Age-related macular degeneration (AMD) is the leading cause of vision loss in people over the age of 60. The disease affects the retina, the paper-thin tissue lining the back of the eye.
In the very center of the retina is the macula, which contains the highest concentration of light-sensitive cells, called cones.
- Cones provide sharp, detailed, central vision used in activities like driving and reading.
- In macular degeneration, cells in the macular region begin to die, causing blind spots and distorted central vision.
The two types of macular degeneration are dry and wet.
- People can develop both types of the disease.
- The disease can affect one or both eyes.
- The disease may progress slowly or rapidly.
Dry macular degeneration may advance and cause vision loss with or without turning into the wet type of the disease. However, not everyone with early AMD will develop the advanced form of the disease.
Dry Macular Degeneration
The most common type of macular degeneration, about 85 to 90 percent of cases, is the dry type:
- The photosensitive cells of the macula slowly break down.
- Yellow protein deposits called drusen (extracellular waste products from metabolism) form and accumulate under the retina between the retinal pigmented epithelium (RPE) layer and the Bruch's membrane, which supports the retina.
- Drusen are often found in the eyes of older people, but an increase in the size and number of these deposits is frequently the first sign of macular degeneration.
- Over time, drusen lead to deterioration of the macula and the death of RPE and photoreceptor cells. This process results in a blurring or spotty loss of clear, straight-ahead vision but does not cause pain.
- In the early stages of the disease, the patient may notice slightly blurry vision. However, as more and more of the cells die, central vision worsens.
- Although dry AMD does not cause complete blindness, in its most advanced form it can cause profound central vision loss, severely affecting a person's quality of life.
The dry type of macular degeneration has three stages:
- Patients have several small or a few medium-sized drusen.
- No vision loss or symptoms occur at this stage.
- Patients have many medium-sized or one or more large drusen.
- Some people may need more light for tasks such as reading.
- A blurry spot may appear in the center of the visual field.
- Patients have a large number of drusen deposits.
- RPE, photoreceptor (light-sensitive) cells and supporting tissue in the retina begin to break down.
- A large blurry spot occurs in the center of the visual field and can become larger and darker, eventually causing a complete loss of central vision.
Wet Macular Degeneration
Wet macular degeneration accounts for approximately 10 percent of the cases of age-related macular degeneration. However, it results in 90 percent of the cases of legal blindness. All wet macular degeneration is considered advanced.
Wet macular degeneration occurs when abnormal blood vessels grow behind the macula as RPE and photoreceptor cells die.
- The Bruch's membrane begins to break down, usually near drusen deposits, and new blood vessels grow.
- This growth is called neovascularization. These vessels are very fragile and can leak fluid and blood.
- The leaks result in scarring of the macula and the potential for rapid, severe damage.
- Straight-ahead vision can become distorted or lost entirely in a short period of time, sometimes within days or weeks.
It’s important to get regular comprehensive eye exams, because AMD has the potential to progress quickly or without obvious symptoms. See “Macular Degeneration: Screening and Diagnosis.”