Eye and vision care

What is age-related macular degeneration?

The most common cause of vision loss among people 50 or older, age-related macular degeneration is a degenerative condition of the macula.

Located roughly in the center of the retina, the macula is a small and highly sensitive part of the retina responsible for detailed central vision. The macula is what determines our visual acuity—that is, our ability to appreciate details and to perform tasks such as reading that require central vision. Age-related macular degeneration is caused by the hardening of the arteries that nourish the retina. As a result, sensitive retinal tissue is deprived of the oxygen and nutrients it needs to survive and central vision may become blurry.

Macular degeneration varies from one person to another and may even vary within a patient, affecting each eye differently. One eye may be severely affected while the other is not. In mild cases, it causes only mild distortion. In advanced cases, however, it causes a complete loss of central vision and makes daily activities such as reading and driving virtually impossible. However, because macular degeneration does not affect peripheral vision, it does not cause total blindness.

Types of macular degeneration

Age-related macular degeneration may be classified as either neovascular (wet) or non-neovascular (dry).

Non-neovascular (dry) age-related macular degneration

Dry macular degeneration is the more common of the two and is typically less severe, resulting in a more gradual loss of vision. Dry macular degeneration is characterized by drusen—small, yellowish deposits that form within the layers of the retina. Drusen themselves do not cause vision loss. However, an increase in the size and number of drusen increases a person's risk of developing either advanced dry macular degeneration or wet macular degeneration.

Dry age-related macular degeneration has three stages, all of which may occur in one or both eyes:

1. Early age-related macular degeneration
   People with early age-related macular degeneration have either several small drusen or a few medium-sized drusen. At this stage, there are no symptoms and patients experience no vision loss.

2. Intermediate age-related macular degeneration
   People with intermediate age-related macular degeneration have either many medium-sized drusen or one or more large drusen. Some people see a blurred spot in the center of their vision. More light may be needed for reading and other tasks.

3. Advanced dry age-related macular degeneration
   In addition to drusen, people with advanced dry age-related macular degeneration have a breakdown of light-sensitive cells and supporting tissue in the central retinal area. This breakdown can cause a blurred spot in the center of your vision. Over time, the blurred spot may get bigger and darker, taking more of your central vision. You may have difficulty reading or recognizing faces until they are very close to you.

Patients experiencing age-related macular degeneration in one eye only may not notice any changes in their overall vision. With the other eye still able to see clearly, they can still drive, read, and see fine details. These patients notice changes in their vision only if both eyes are affected. People whose vision is blurry are encouraged to see an eye care professional for a comprehensive eye exam.

Neovascular (wet) age-related macular degneration

Although rare—affecting only approximately 10 percent of all patients with age-related macular degeneration—wet macular degeneration occurs when new blood vessels form to improve blood supply to the oxygen-deprived retinal tissue. Unlike normal vessels, however, these new vessels are very fragile, making them more prone to breakage. When these new vessels break, they cause swelling, hemorrage, and scar tissue.

Unlike dry macular degeneration, wet macular degeneration has no early or intermediate signs and therefore, is considered advanced age-related macular degeneration.

Both wet and dry age-related macular degeneration are considered advanced; vision loss occurs in either form, and only advanced age-related macular degeneration can cause vision loss. People who have advanced age-related macular degeneration in one eye are at especially high risk of developing it in the other eye.

What causes macular degeneration?

Genetic factors and age, as well as lifestyle factors such as smoking and nutrition can play a role in the development of macular degeneration. Known risk factors include:

• smoking
• obesity
• race—Caucasians are at higher risk than Blacks
• gender—women appear to be at higher risk than men
• family history—people with a family history of age-related macular degeneration are at higher risk of getting the disease

It's also believed there is a link between exposure to sunlight and macular degeneration.

What are the signs and symptoms of macular degeneration?

Macular degeneration may be characterized by some or all of the following symptoms:

• Loss of central vision may be gradual in dry macular degeneration. Patients suffering from wet macular degeneration suffer a sudden decrease of central vision.
• Difficulty performing tasks requiring the ability to see detail (i.e. reading, sewing)
• Distorted vision in which straight lines may appear wavy or bent.

If you experience any of the above symptoms, be sure to consult with your ophthalmologist right away.

How is macular degeneration diagnosed?

An ophthalmologist can detect macular degeneration through a retinal examination. Various tests are conducted to determine what damage has been done to the retina. The simplest of these tests is a vision test, in which you will be asked to read letters on an eye chart. Your ophthalmologist may also perform additional tests, including the Amsler grid test, ophthalmoscopy, fundus photography and fluorescein angiography. Each of these tests is described in further detail below.

Amsler grid test

The Amsler grid test is designed to test a patient's central vision by assessing the macula. The patient fixes on a small dot located in the center of a grid consisting of evenly spaced horizontal and vertical lines. While fixating on the center dot, the patient looks for wavy lines and missing areas of the grid. If you have trouble seeing the sides or corners of the grid, if any of the lines appear wavy rather than straight or parallel, or if you notice any holes or areas missing from the grid, your ophthalmologist will want to examine your macula very closely to determine whether you have macular degeneration. This is done through ophthalmoscopy (see below).

The Amsler grid test is often given to patients for home use to monitor macular degeneration. When doing the test at home, be sure to notify your ophthalmologist of any changes in the appearance in the Amsler grid.

Ophthalmoscopy

Opthalmoscopy is used to examine inside the eye. Before performing this test, your doctor will need to dilate your pupils with drops. Dilation gives the best view of the inside of the eye.

In a darkened room, the doctor will examine your eyes using an ophthalmoscope—a device with a light at the end that will magnify the eye, allowing the doctor to look inside and examine the retina, vitreous, and optic nerve.

There are two types of ophthalmoscopes: direct and indirect. A direct ophthalmoscope is a hand-held device with a series of lenses that allow the doctor to focus on the central retina. An indirect ophthalmoscope is worn on the doctor's head. While looking through the ophthalmoscope's magnifying glasses, a special lens is placed in front of a patient's eye, giving the doctor a clear view of the retina.

Fundus photography

Fundus photography uses a highly specialized camera mounted to a microscope to take pictures of the back of a patient's eye. These photos are used to document the health of the optic nerve, vitreous, macula, retina, and blood vessels; they are used for comparison and documentation, and they are useful in the diagnosis of certain eye conditions.

Before the photos are taken, a patient's pupils are dilated with drops. Dilation is necessary, since the pupil would otherwise constrict from the brightness of the camera flash. By focusing light through a patient's cornea, pupil, and lens, the photographer is able to focus high-powered lenses to take photos of the back of a patient's eye. The process of fundus photography usually takes between 5 and 10 minutes.

Fluorescein angiography

In fluorescein angiography, a dye called fluorescein is injected into a vein in a patient's arm. The dye quickly travels to the blood vessels inside the eye. A highly specialized camera equipped with special filters is then used to take pictures of the retina. The filters highlight the fluorescein as it travels through the blood vessels in the back of the eye. Patterns and changes in the dye reveal any circulation problems, swelling, leaking, or abnormal blood vessels and will indicate to your doctor the presence of eye conditions requiring attention.

How is macular degeneration treated?

Treatment of dry age-related macular degeneration

No form of treatment can prevent vision loss once dry age-related macular degeneration reaches the advanced stage. However, treatment can delay and possibly prevent intermediate age-related macular degeneration from progressing to the advanced stage. A study by the National Eye Institute found that taking a specific high-dose formulation of antioxidants and zinc significantly reduces the risk of advanced age-related macular degeneration. Slowing the progression of age-related macular degeneration from the intermediate stage to the advanced stage will undoubtedly help preserve the vision of many patients.

Treatment of wet age-related macular degeneration

Two treatments are available for patients living with wet age-related macular degeneration: laser surgery and photodynamic therapy. Although neither is a cure and although the disease and vision loss may progress despite treatment, these treatments may slow vision loss and help prevent further loss of vision.

1. Laser surgery
   Laser surgery is used to destroy fragile, leaky blood vessels. During this procedure, a laser is aimed directly onto the new blood vessels, destroying them and preventing further loss of vision. This type of surgery carries the risk that some surrounding healthy tissue and some vision may also be destroyed. There is also the risk that new blood vessels may develop following treatment. Repeated treatments may be necessary.

   Only a small percentage of people with wet age-related macular degeneration can be treated with laser surgery; the procedure is more effective if the leaking blood vessels have developed away from the fovea.

2. Photodynamic therapy
   In photodynamic therapy, a drug called verteporfin is injected into a patient's arm. The verteporfin then travels throughout the body and into the new blood vessels in the eye. Verteporfin has a tendency to adhere to the surface of new blood vessels. A light is then shone into the eye for a period of 90 seconds, activating the drug. Once activated, the verteporfin destroys the new blood vessels and leads to a slower rate of vision loss. Unlike laser surgery, verteporfin does not destroy surrounding healthy tissue. However, because the drug is activated by light, you will be instructed to avoid direct sunlight and bright indoor light for a period of five days following treatment. Photodynamic therapy is painless and is typically performed on an outpatient basis in an ophthalmologist's office. The entire procedure takes about 20 minutes.

   Photodynamic therapy slows vision loss. It doesn't stop vision loss or restore vision in eyes already affected by advanced age-related macular degeneration. Results of photodynamic therapy are often temporary, and you may require repeated treatments.