The federal government estimates that 135 million people worldwide suffer from low vision, a visual impairment, not correctable by standard glasses, contact lenses, medicine, or surgery, that interferes with a person’s ability to perform everyday activities.
Age-related macular degeneration is a common eye condition that normally affects those who are age 50 or older. The disease may spread rapidly or may spread so slowly that it remains undetectable for a period of time.
The macula is made up of millions of light-sensing cells that provide sharp, central vision. It is the most sensitive part of the retina, which is located at the back of the eye. The retina turns light into electrical signals and then sends these electrical signals through the optic nerve to the brain, where they are translated into the images we see. When the macula is damaged, the center of your field of view may appear blurry, distorted, or dark.
Risk factors for AMD include race, smoking, genetics and family history. According to the National Eye Institute,
The early and intermediate stages of AMD usually start without symptoms. Only a comprehensive dilated eye exam can detect AMD. The eye exam may include the following:
- Visual acuity test. This eye chart measures how well you see at distances.
- Dilated eye exam. Your eye care professional places drops in your eyes to widen or dilate the pupils. This provides a better view of the back of your eye. Using a special magnifying lens, he or she then looks at your retina and optic nerve for signs of AMD and other eye problems.
- Amsler grid. Your eye care professional also may ask you to look at an Amsler grid. Changes in your central vision may cause the lines in the grid to disappear or appear wavy, a sign of AMD.
- Fluorescein angiogram. In this test, which is performed by an ophthalmologist, a fluorescent dye is injected into your arm. Pictures are taken as the dye passes through the blood vessels in your eye. This makes it possible to see leaking blood vessels, which occur in a severe, rapidly progressive type of AMD (see below). In rare cases, complications to the injection can arise, from nausea to more severe allergic reactions.
- Optical coherence tomography. You have probably heard of ultrasound, which uses sound waves to capture images of living tissues. OCT is similar except that it uses light waves, and can achieve very high-resolution images of any tissues that can be penetrated by light—such as the eyes. After your eyes are dilated, you’ll be asked to place your head on a chin rest and hold still for several seconds while the images are obtained. The light beam is painless.
During the exam, your eye care professional will look for drusen, which are yellow deposits beneath the retina. Most people develop some very small drusen as a normal part of aging. The presence of medium-to-large drusen may indicate that you have AMD.
Another sign of AMD is the appearance of pigmentary changes under the retina. In addition to the pigmented cells in the iris (the colored part of the eye), there are pigmented cells beneath the retina. As these cells break down and release their pigment, your eye care professional may see dark clumps of released pigment and later, areas that are less pigmented. These changes will not affect your eye color.
February is dedicated to issues concerning low vision and age-related macular degeneration. Organizations such as Lighthouse of Pinellas, the National Eye Institute, and others are increasing awareness of such eye disorders through information campaigns and programs to assist those who suffer from these eye disorders.