Macular Degeneration
The retina is the most internal layer of the eye. Using an analogy, it is for the eye what the photographic film is for a camera. The purpose of all the other optical systems of the eye is to make sure that the light from the object upon which the person fixates comes into focus on the retina, forming there a clear image. The image is then processed into electric impulses within the retina and transmitted to the brain through the optic nerve.
Obviously, any disease or alteration in the retina will impede all the above mentioned process.
There are many such conditions, but by their frequency and seriousness we mention two of them: Age-related Macular Degeneration and Diabetic Retinopathy. Click on their names to learn more about them.
Macular Degeneration (Age-Related Type)
Macular degeneration is a disease that affects central vision and leads to loss of vision. Although there are forms of macular degeneration that strike young people, the condition occurs most commonly in people who are over 60 years of age. This disorder is thus called age-related macular degeneration (AMD).
Does age-related macular degeneration cause blindness?
As a general rule, no. Because only the center of a person's vision is usually affected, blindness rarely occurs from the disease. However, injury to the macula in the center of the retina can destroy the ability to see straight ahead clearly. Therefore, AMD can sometimes make it difficult to read, drive, or perform other daily activities that require fine central vision.
What is the macula?
The macula is in the center of the retina, the light-sensitive paper-thin layer of tissue at the back of the eye. As we read, light is focused onto the macula. In the macula, millions of cells change the light into nerve signals that travel to the brain and tell it what we are seeing. This is called our central vision. With normal central vision, we are able to read, drive, and perform other activities that require fine, sharp, straight-ahead vision.
There are two forms of AMD. Each damages vision in its own way. The two forms are:
- Dry AMD: Dry AMD causes most cases (about 90%) of AMD. However, it only accounts for 10% of all blindness from AMD.
- Wet AMD: The situation with wet AMD is exactly the opposite: it causes only 10% of AMD but accounts for 90% of all blindness from AMD.
What happens in dry AMD?
In dry AMD, the light sensitive cells in the macula slowly break down. With less of the macula functioning, central vision diminishes. Dry AMD often occurs in just one eye at first. Later, the other eye can be affected. Doctors have no way of knowing if or when both eyes may become involved. The cause of dry AMD is unknown.
How does wet AMD occur?
Wet AMD occurs when new blood vessels behind the retina start to grow toward the macula. Because these new blood vessels tend to be very fragile, they will often leak blood and fluid under the macula. This causes rapid damage to the macula that can lead to the loss of central vision in a short period of time.
Who is most likely to develop AMD?
Factors that influence the risk for developing AMD include:
- Age: Age is the most powerful risk factor. Although AMD can occur during middle age, the risk of developing the condition rises sharply thereafter. People in their 50s have about a 2% chance of contracting AMD. This likelihood rises to nearly 30% over age 75.
- Gender: Women tend to be at greater risk than men.
- Smoking: Smoking increases the risk of AMD.
- Family history of AMD: People with AMD in the family are at higher risk of developing the disease.
- Cholesterol: People with elevated levels of blood cholesterol may be at higher risk for wet AMD.
What are the symptoms of dry AMD?
Dry AMD does not cause pain. The most common symptom of dry AMD is slightly blurred vision. The person may need more light for reading and other tasks. Also, the patient may find it hard to recognize faces until the person is very close to them. As dry AMD worsens, the individual may see a blurred spot in the center of their vision. This spot occurs because a group of cells in the macula have stopped working. Over time, the blurred spot may get bigger and denser, taking more of the patient's central vision.
People with dry AMD in one eye often do not notice any changes in their vision. With one eye seeing clearly, they can still drive, read, and see fine details. Some people may notice changes in their vision only if AMD affects both of their eyes.
What are the symptoms of wet AMD?
Wet AMD also does not cause pain. An early symptom of wet AMD is that straight lines appear wavy. Another sign that a person may have wet AMD is rapid loss of central vision. This is different from dry AMD in which loss of central vision occurs slowly.
If any of these changes in vision is noticed, an eye care specialist (an ophthalmologist) should immediately be consulted.
How is AMD diagnosed?
AMD is detected during a thorough eye examination that includes:
- Visual acuity test: This eye chart test measures how well a person sees at various distances.
- Pupil dilation: This examination enables the eye care professional to see more of the retina and look for signs of AMD. To do this, drops are placed into the eye to dilate (widen) the pupil. After the examination, the patient's vision may remain blurred for several hours.
- Tonometry: This is a standard test that determines the fluid pressure inside the eye. Increased pressure is a possible sign of glaucoma, another common eye problem in people over age 60.
- Drusen: One of the most common early signs of AMD is the presence of drusen. Drusen are tiny yellow deposits in the retina. The eye care specialist can see them during an eye examination. The presence of drusen alone does not indicate a disease, but it might mean that the eye is at risk for developing more severe AMD.
- Amsler grid: While conducting the examination, the eye care professional may ask the patient to look at an Amsler grid. This grid is a pattern that resembles a checker board. The patient covers one eye and stares at a black dot in the center of the grid. While staring at the dot, the patient may notice that the straight lines in the pattern appear wavy. This can be a sign of wet AMD.
Amsler grid:
These grids are reduced in size; eye care specialists have full-size grids to use at home.
- Fluorescein angiography: If the eye care professional suspects the patient has wet AMD, the patient may need to have a test called fluorescein angiography. In this test, a special dye is injected into a vein in the arm. Pictures are then taken as the dye passes through the blood vessels in the retina. The photos help detect and evaluate leaking blood vessels to determine whether they can be treated.
How is dry AMD treated?
In some cases, wet AMD can be treated with laser surgery. The treatment involves aiming a high energy beam of light directly onto the leaking blood vessels to seal them. Laser treatment is best when done soon after the new blood vessels develop, before they have reached and damaged the fovea-the central part of the macula. But even if the blood vessels are growing right behind the fovea, the treatment can be of some value in stopping further vision loss.
How is laser surgery done?
Laser surgery is performed in the eye specialist's office or eye clinic. Before the surgery, the doctor dilates the patient's pupil and applies drops to numb the eye. In some cases, the doctor also may numb the area behind the eye to prevent any discomfort. The lights in the office are dimmed. As the patient sits facing the laser machine, the doctor holds a special lens to the patient's eye. The patient may see flashes of bright green or red light.
The patient can leave the office once the treatment is done, but will need someone to drive them home. Because the pupils remain dilated for a few hours, the patient should bring a pair of sunglasses. For the rest of the day, the patient's vision may be a little blurry. The eye may also hurt a bit. This is easily controlled with drugs that the eye care professional can suggest. The patient usually needs to make frequent follow-up visits. During each exam, the patient may have fluorescein angiography to make sure that the blood vessels are not still leaking. If the vessels continue to leak, the patient might require additional laser surgery.
Is there any other way to slow down wet AMD?
It has been reported that supplements of zinc and the antioxidants vitamin C, vitamin E and beta-carotene can slow the progression of wet AMD. In people with intermediate-stage disease, zinc reduced the risk of the disease progressing to the advanced stage by 11%, and the antioxidants reduced the risk by 10%. When the two were combined, the risk was reduced by 19%. The daily doses of the antioxidants used in the study were 500 milligrams of vitamin C, 400 milligrams of vitamin E and 15 milligrams of beta-carotene (a molecule the body converts to vitamin A). The daily dose of zinc was 80 milligrams with 2 milligrams of copper. These amounts are well above the usual levels recommended by the Food and Drug Administration (FDA): 3 times as much vitamin A, 8 times as much vitamin C, 13 times as much vitamin E and 5 times as much zinc.
What can a person with dry AMD do to protect their vision?
If a person has wet AMD, it is important not to delay laser surgery if the eye care professional advises them to have it. After surgery, the patient will need to have frequent eye examinations to detect any recurrence of leaking blood vessels.
Persons who smoke must stop. Studies show that people who smoke have a greater risk of recurrence of wet AMD than those who don't.
In addition, the patient should continue to check their own vision at home with the Amsler grid and/or other methods exactly as described above for dry AMD. The patient should schedule an eye exam immediately if there is any change in vision.
What can a person do if he or she has already lost some vision to AMD?
Normal use of the eyes will not cause further damage to vision. Even if a person has lost some sight to AMD, they should not be in the least afraid to use their eyes for reading, watching TV, and other usual activities.
Low vision aids are available to help a patient make the most of their remaining vision. Low vision aids are special lenses or electronic systems that make images appear larger. If a patient needs low vision aids, the eye care professional can often refer the patient to a low vision specialist.
Macular Degeneration At A Glance
- The macula is in the center of the retina, the light-sensitive layer of tissue at the back of the eye.
- The macula is responsible for central vision (straight-ahead vision).
- Degeneration of the macula occurs most often after the age of 60 years and is termed age-related macular generation (AMD).
- Smoking increases the risk of AMD.
- AMD is a painless condition.
- There are two types of AMD: dry AMD and wet AMD.
- Early symptoms of dry AMD include slightly blurred vision, the need for more light for reading, and difficulty recognizing faces until very close to the person.
- A symptom of more advanced dry AMD is the presence of a blurred spot in the center of vision.
- Dry AMD cannot be treated at present.
- An early symptom of wet AMD is the wavy appearance of straight lines.
- Early diagnosis of wet AMD is particularly critical; if in doubt, go to the doctor.
- Laser surgery can save sight in wet AMD.
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