Diagnosing Age-Related Macular Degeneration
NYU Langone ophthalmologists use a number of vision and imaging tests to diagnose age-related macular degeneration.
Age-related macular degeneration is an eye condition in which a part of the eye called the macula begins to deteriorate. The macula enables you to see objects directly in front of you—an ability known as central vision. It’s located near the center of the retina, the light-sensitive layer of tissue at the back of the inner eye that gives you sight.
The disease is considered to be “age-related” because people older than 60 years old are more likely to develop this condition. This risk continues to increase with age.
Age-related macular degeneration may affect one or both eyes.
Symptoms and Causes of Macular Degeneration
In some people, macular degeneration advances so slowly that vision loss does not occur for a long time—if at all. In others, the disease progresses more quickly and may affect vision in one or both eyes.
People with macular degeneration may see wavy lines instead of straight ones in the center of their field of vision, or objects may appear blurry. They may have trouble reading or see geometric shapes.
Other people with aggressive forms of macular degeneration may completely lose central vision. Although the ability to see can be greatly impaired, people with macular degeneration do not become entirely blind. They still retain peripheral vision.
Doctors don’t know what causes macular degeneration, but most experts believe retinal tissue weakens with age, putting people at risk for this condition. Other risk factors include smoking, high blood pressure, high cholesterol, and significant sun exposure, which can harm the eyes. In addition, obesity may also increase a person's risk of developing macular degeneration
A family history of macular degeneration may also increase your chances of developing it. Certain genes are associated with the condition. Researchers are studying whether genetic testing can help determine the best treatment approach.
There are two types of macular degeneration: dry, or non-neovascular, and wet, or neovascular. The term neovascular refers to the growth of new blood vessels in an area where they are not meant to grow.
About 90 percent of people diagnosed with macular degeneration have the dry form. Approximately 10 percent of people with macular degeneration have the wet type, which is a more progressive form of the disease. All people with the wet form of this condition have also had the dry type of macular generation.
Because dry macular degeneration may eventually develop into the wet type, doctors at NYU Langone carefully monitor people with even the earliest forms of the condition, using different types of eye exams.
Dry Macular Degeneration
In dry macular degeneration, there are yellow deposits, called drusen, in the macula. Drusen is the German word for “bump,” and your doctor determines what stage of dry macular degeneration you have based on the number, size, and characteristics of the drusen in your eye.
Dry macular degeneration usually progresses slowly. Many people find they are able to participate in their regular activities, especially if only one eye is affected.
In the early stages, you may have a few small drusen, but this is generally not cause for alarm. Most older people have a few drusen in their macula as a result of the aging process. Most of the time, there are no changes in vision.
If the drusen begin to grow in size and increase in number, in what is considered intermediate dry macular degeneration, you may notice a dimming or distortion of vision when you read.
In the more advanced stages of the condition, doctors detect several large drusen as well as a thinning of the light-sensitive layer of cells in the macula. This can cause the macular tissue to die, or atrophy, potentially causing blind spots in the center of the field of vision or a complete loss of central vision.
If you have this form of macular degeneration, your doctor assesses the risk of the condition progressing to the wet form of the disease.
Wet Macular Degeneration
Some people diagnosed with dry macular degeneration go on to develop the wet form of the condition. This type is known for the growth of abnormal blood vessels underneath the macula. These vessels leak blood and fluid into the retina, interfering with its function. The wet form of the disease is more aggressive than the dry type.
Wet macular degeneration can develop abruptly, sometimes even over the course of a few days. You may notice that your vision is distorted, or that straight lines look wavy. You may also experience blind spots and a sudden loss of central vision.
If the leaking from these abnormal blood vessels is not controlled, it can eventually lead to scarring and a permanent loss of central vision.
Determining whether you have the dry or wet form of age-related macular degeneration, and how advanced it is, helps your ophthalmologist decide how to best manage the condition.
To diagnose macular degeneration, NYU Langone doctors ask about your symptoms. For example, they may want to know whether you are having problems with your vision. They also perform a comprehensive eye exam and all or some of the following tests.
Visual Acuity Test
In this simple and likely familiar exam, a doctor asks you to view and read aloud from a chart with letters of various sizes. This test measures how well you can see and whether your distance vision has been affected.
Dilated Eye Exam
During a dilated eye exam, your ophthalmologist puts drops in your eyes to dilate, or widen, the pupils. This enables your doctor to examine the back of the eye.
Using a special magnifying lens, your doctor checks the retina and optic nerve for signs of macular degeneration and other eye problems.
Optical Coherence Tomography
Before performing optical coherence tomography, the doctor puts drops in your eyes to dilate the pupils. With a special machine, the doctor then uses light to scan your eye and take high-resolution images of sections of the macula to look for fluid and changes that accompany macular degeneration.
After diagnosis, this painless exam can also help determine whether the condition is changing or getting worse.
During a fluorescein angiogram, your doctor injects a fluorescent dye into your arm. Then, using a special camera, he or she takes pictures as the dye passes through the blood vessels in your eye. This helps your ophthalmologist to look for leaking blood vessels, which occur in the wet form of macular degeneration.
A fluorescein angiogram is considered to be a safe procedure; however, rarely, people experience complications from the dye, ranging from nausea to a severe allergic reaction.
Fundus Autofluorescence Imaging
With fundus autofluorescence imaging, doctors use a special camera to take pictures of the fluorescence, or the emission of light, from pigments found in the retina. These images enable physicians to identify microscopic changes and patterns in the retina pigments that may be caused by macular degeneration.
An Amsler grid is a chart filled with horizontal and vertical lines. Although doctors at NYU Langone may not use this grid for diagnosis, some people with macular degeneration may use it to monitor their condition.
You view the chart from about the same distance as you would view reading material, covering each eye. Any changes that occur in the center of your field of vision may cause the lines in the grid to disappear or seem wavy and may be a sign that macular degeneration is progressing.