Amd | Health Knowledgebase

Age Related Macular Degeneration (AMD)

3rd December, 2008 - Posted by Andy - No Comments

Introduction

Age-related macular degeneration is a disease that blurs the sharp, central vision you need for “straight-ahead” activities such as reading, sewing, and driving. AMD affects the macula, the part of the eye that allows you to see fine detail, but causes no pain. In some cases, AMD advances so slowly that people notice little change in their vision. In others, the disease progresses faster and may lead to a loss of vision in both eyes. AMD is a leading cause of vision loss in British people 60 years of age and older.

The macula is located in the centre of the retina, the light-sensitive tissue at the back of the eye. The retina instantly converts light, or an image, into electrical impulses and then sends these impulses, or nerve signals, to the brain

VARIATIONS OF AMD

Wet AMD occurs when abnormal blood vessels behind the retina start to grow under the macula. These new blood vessels tend to be very fragile and often leak blood and fluid which raise the macula from its normal place at the back of the eye. Unfortunately, damage to the macula occurs rapidly, and loss of central vision can occur quickly. Wet AMD is considered to be advanced AMD and is more severe than the dry form.

An early symptom of wet AMD is that straight lines appear wavy. If you notice this condition or other changes to your vision, contact your local eye hospital.

Dry AMD occurs when the light-sensitive cells in the macula slowly break down, gradually blurring central vision in the affected eye. As dry AMD gets worse, you may see a blurred spot in the centre of your vision. Over time, as less of the macula functions, central vision in the affected eye can be lost gradually. The most common symptom of dry AMD is slightly blurred vision; you may have difficulty recognising faces; you may need more light for reading and other tasks. Dry AMD generally affects both eyes, but vision can be lost in one eye while the other eye seems unaffected.

One of the most common early signs of dry AMD is drusen. Drusen are yellow deposits under the retina and are often found in people over age 60. Dry AMD has three stages, all of which may occur in one or both eyes:

Early AMD. People with early AMD have either several small drusen or a few medium-sized drusen. At this stage, there are no symptoms and no vision loss.

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

Advanced Dry AMD. In addition to drusen, people with advanced dry AMD have a breakdown of light-sensitive cells and supporting tissue in the central retinal area. This breakdown can cause a blurred spot in the centre 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 recognising faces until they are very close to you.
If you have vision loss from dry AMD in one eye only, you may not notice any changes in your overall vision. With the other eye seeing clearly, you still can drive, read, and see fine details. You may notice changes in your vision only if AMD affects both eyes. If blurriness occurs in your vision, see an eye care professional for a comprehensive dilated eye exam

Drusen alone do not usually cause vision loss. In fact, scientists are unclear about the connection between drusen and AMD - they know, for example, that an increase in the size or number of drusen raises a person’s risk of developing either advanced dry AMD or wet AMD. These changes can cause serious vision loss.

TESTING
AMD is detected during a comprehensive eye exam that includes:

Visual acuity test. This eye chart test measures how well you see at various distances.
Dilated eye exam. Drops are placed in your eyes to widen, or dilate, the pupils. Your eye care professional uses a special magnifying lens to examine your retina and optic nerve for signs of AMD and other eye problems. After the exam, your close-up vision may remain blurred for several hours.
Tonometry. An instrument measures the pressure inside the eye. Numbing drops may be applied to your eye for this test.

During an eye exam, you may be asked to look at an Amsler grid. The pattern of the grid resembles a checkerboard. You will cover one eye and stare at a black dot in the centre of the grid. While staring at the dot, you may notice that the straight lines in the pattern appear wavy. You may notice that some of the lines are missing. These may be signs of AMD.

If your eye consultant believes you need treatment for wet AMD, he or she may suggest a fluorescein angiogram. In this test, a special dye is injected into your arm. Pictures are taken as the dye passes through the blood vessels in your retina. The test allows your eye care professional to identify any leaking blood vessels and recommend treatment.

TREATMENTS
Once dry AMD reaches the advanced stage, no form of treatment can prevent vision loss. However, treatment can delay and possibly prevent intermediate AMD from progressing to the advanced stage, in which vision loss occurs. The US National Eye Institute’s Age-Related Eye Disease Study (AREDS) found that taking a specific high-dose formulation of antioxidants and zinc significantly reduces the risk of advanced AMD and its associated vision loss. Slowing AMD’s progression from the intermediate stage to the advanced stage will save the vision of many people.

The specific daily amounts of antioxidants and zinc used by the study researchers were 500 milligrams of vitamin C, 400 International Units of vitamin E, 15 milligrams of beta-carotene (often labelled as equivalent to 25,000 International Units of vitamin A), 80 milligrams of zinc as zinc oxide, and two milligrams of copper as cupric oxide. Copper was added to the AREDS formulation containing zinc to prevent copper deficiency anaemia, a condition associated with high levels of zinc intake. People who are at high risk for developing advanced AMD should consider taking the formulation. You are at high risk for developing advanced AMD if you have either: Intermediate AMD in one or both eyes OR Advanced AMD (dry or wet) in one eye but not the other eye.

Wet AMD can be treated with laser surgery, photodynamic therapy, and injections into the eye. None of these treatments is a cure for wet AMD. Each treatment may slow the rate of vision decline or stop further vision loss, but the disease and loss of vision may progress despite treatment.

Laser surgery This procedure uses a laser to destroy the fragile, leaky blood vessels. A high energy beam of light is aimed directly onto the new blood vessels and destroys them, preventing further loss of vision. However, laser treatment also may destroy some surrounding healthy tissue and some vision. Only a small percentage of people with wet AMD can be treated with laser surgery. Laser surgery is more effective if the leaky blood vessels have developed away from the fovea, the central part of the macula. Laser surgery is performed in a doctor’s office or eye clinic.

The risk of new blood vessels developing after laser treatment is high. Repeated treatments may be necessary. In some cases, vision loss may progress despite repeated treatments.

Photodynamic therapy A drug called verteporfin is injected into your arm. It travels throughout the body, including the new blood vessels in your eye. The drug tends to “stick” to the surface of new blood vessels. Next, a light is shined into your eye for about 90 seconds. The light activates the drug. The activated drug destroys the new blood vessels and leads to a slower rate of vision decline. Unlike laser surgery, this drug does not destroy surrounding healthy tissue. Because the drug is activated by light, you must avoid exposing your skin or eyes to direct sunlight or bright indoor light for five days after treatment. Photodynamic therapy is relatively painless. It takes about 20 minutes and can be performed in a consultant’s office.

Photodynamic therapy slows the rate of vision loss. It does not stop vision loss or restore vision in eyes already damaged by advanced AMD. Treatment results often are temporary. You may need to be treated again.

Injections Wet AMD can now be treated with a new drug that is injected into the eye (anti-VEGF therapy). Abnormally high levels of a specific growth factor occur in eyes with Wet AMD and promote the growth of abnormal new blood vessels. This drug treatment blocks the effects of the growth factor. You will need multiple injections, usually given about six weeks apart. The eye is numbed before each injection. After the injection, you will remain in the doctor’s office for a while and your eye will be monitored. As with photodynamic therapy, the main benefit for patients treated with the drug is to slow vision loss from AMD.

PROTECTING YOUR VISION
If you have dry AMD, you should have a comprehensive dilated eye exam at least once a year. Also, if you have intermediate AMD in one or both eyes, or advanced AMD in one eye only, your doctor may suggest that you take the AREDS formulation containing the high levels of antioxidants and zinc.

Because dry AMD can turn into wet AMD at any time, you should get an Amsler grid from your eye care professional. Use the grid every day to evaluate your vision for signs of wet AMD. This quick test works best for people who still have good central vision. Check each eye separately. Cover one eye and look at the grid. Then cover your other eye and look at the grid. If you detect any changes in the appearance of this grid or in your everyday vision while reading the newspaper or watching television, get a comprehensive dilated eye exam.

If you have wet AMD and your doctor advises treatment, do not wait. After laser surgery or photodynamic therapy, you will need frequent eye exams to detect any recurrence of leaking blood vessels. Studies show that people who smoke have a greater risk of recurrence than those who don’t. In addition, check your vision at home with the Amsler grid. If you detect any changes, schedule an eye exam immediately.

Finally, your lifestyle can play a role in reducing your risk of developing AMD. Eat a healthy diet high in green leafy vegetables and fish; Don’t smoke; Maintain normal blood pressure; Watch your weight; Exercise regularly

[Sources: StLukeseye.com, NHS Direct, NIH (USA)]

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FURTHER READING
http://www.merck.com
http://www.medicinenet.com/macular_degeneration_age-related_type/article.htm
http://www.lighthouse.org
http://www.medic8.com/eye-disorders/macular-degeneration.htm
http://www.stlukeseye.com