dot dot
dot
เนื้อหาภาษาไทย
dot
bulletNews and Events
dot
Newsletter

dot


AMD article

Age-related macular degeneration is a chronic eye disease that occurs when tissue in the macula, the part of your retina that's responsible for central vision, deteriorates. The retina is the layer of tissue on the inside back wall of your eyeball. Degeneration of the macula causes blurred central vision or a blind spot in the center of your visual field.

The first sign of macular degeneration may be a need for more light when you do close-up work. Fine newsprint may become harder to read and street signs more difficult to recognize. Gray or blank spots may mask the center of your visual field. The condition usually develops gradually, but sometimes progresses rapidly, leading to severe vision loss in one or both eyes.

Macular degeneration affects your central vision, but not your peripheral vision; thus it doesn't cause total blindness. Still, the loss of clear central vision — critical for reading, driving, recognizing people's faces and doing detail work — greatly affects your quality of life. The condition tends to develop as you get older, hence the "age-related" part of its name. Macular degeneration is the leading cause of severe vision loss in people age 60 and older.

The damage caused by macular degeneration can't be reversed, but early detection and treatment may help reduce the extent of vision loss.Causes

Signs and symptoms

Macular degeneration usually develops gradually and painlessly. The signs and symptoms of the disease may vary, depending on which of the two types of macular degeneration you have: dry or wet.

Dry macular degeneration
With dry macular degeneration you may notice the following symptoms:

  • The need for increasingly bright illumination when reading or doing close work
  • Increasing difficulty adapting to low levels of illumination, such as when entering a dimly lit restaurant
  • Increasing blurriness of printed words
  • A decrease in the intensity or brightness of colors
  • Difficulty recognizing faces
  • Gradual increase in the haziness of your overall vision
  • Blurred or blind spot in the center of your visual field combined with a profound drop in your central vision acuity

Wet macular degeneration
With wet macular degeneration, the following symptoms may appear, and they may progress rapidly:

  • Visual distortions, such as straight lines appearing wavy or crooked, a doorway or street sign that seems out of whack, or objects appearing smaller or farther away than they should
  • A decrease in or loss of central vision
  • Central blurry spot

In either form of macular degeneration, your vision may falter in one eye while the other remains fine for years. You may not notice any or much change because your good eye compensates for the weak one. Your vision and lifestyle begin to be dramatically affected when this condition develops in both eyes.

Hallucinations
Additionally, some people with macular degeneration may experience visual hallucinations as their vision loss increases. These hallucinations may include unusual patterns, geometric figures, animals or even grotesque-appearing faces. Many people who develop these symptoms are afraid to discuss them with their doctors or friends and families for fear they'll be considered crazy. However, while these hallucinations may be frightening, they're not a sign of mental illness. In fact, these hallucinations are so common that there's a name for this phenomenon — Charles Bonnet syndrome. Feel free to discuss these symptoms with your ophthalmologist.

 CAUSES

The macula is at the back of your eye in the center of your retina. You need a healthy macula for normal central vision acuity. The macula is made up of densely packed light-sensitive cells called cones and rods. These cells, particularly the cones, are essential for central vision. The cones are responsible for color vision, and the rods enable you to see shades of gray.

The choroid is an underlying layer of blood vessels that nourishes the cones and rods of the retina. A layer of tissue forming the outermost surface of the retina is called the retinal pigment epithelium (RPE). The RPE is a critical passageway for nutrients from the choroid to the retina and helps remove waste products from the retina to the choroid.

As you age, the RPE may deteriorate, lose its pigment and become thin (a process known as atrophy), which sets off a chain of events. The nutritional and waste-removing cycles between the retina and the choroid are interrupted. Waste deposits begin to form. Lacking nutrients, the light-sensitive cells of the macula become damaged. The damaged cells can no longer send normal signals through the optic nerve to your brain, and your vision becomes blurred. This is often the first symptom of macular degeneration.

Macular degeneration occurs in two types:

  • Dry macular degeneration. Most people with macular degeneration have the dry form. In fact, macular degeneration almost always starts out as the dry form. The dry form may initially affect only one eye but, in most cases, both eyes eventually become involved. Dry macular degeneration occurs when the RPE cells begin to atrophy and lose their pigment. The normally uniform reddish color of the macula takes on a mottled appearance because of the patchy loss of pigment. Drusen, which look like yellow dots, are fatty-like deposits that appear under the light-sensing cells in the retina.

    Dry macular degeneration is the result of a deterioration of the RPE brought on by aging. The light-sensitive cells of the macula continuously shed used-up outer segments as waste. This waste is broken down and disposed of by the RPE into the choroid. At the same time, cones and rods continuously produce new outer segments to replace the discarded ones.

    When you develop dry macular degeneration, the waste disposal system falls apart. Aging slows the process to a point where waste starts to accumulate in the RPE. This accumulation interferes with the normal function of the RPE, causing the light-sensitive cells of the macula (both cones and rods) to degenerate.

    Initially, in spite of these developments, you may notice little or no change in your vision. Many people who've received a diagnosis of early-stage dry macular degeneration may not be bothered with symptoms, such as blurred eyesight, unless they live to a very old age. But as the drusen and mottled pigmentation continue to develop, your vision may deteriorate. Thinning of the RPE may progress to a point where this protective layer of the retina disappears. This affects the overlying cones and rods and may result in complete loss of your central vision.

  • Wet macular degeneration. The wet form accounts for about 15 percent of all cases, but it's responsible for most of the severe vision loss that people with macular degeneration experience. If you develop wet macular degeneration in one eye, your odds of getting it in the other eye increase greatly. Almost everyone with the wet form of the disease started out with the dry form.

    Wet macular degeneration develops when new blood vessels grow from the choroid underneath the macular portion of the retina. These new vessels are called choroidal neovascularizations (CNVs). These vessels leak fluid or blood, which is why it's called wet macular degeneration. This causes your central vision to blur. Eyes with the wet form of macular degeneration almost always show signs of the dry form, that is, drusen and mottled pigmentation of the retina. In addition, what should be straight lines in your sight become wavy or crooked, and blank spots appear in your field of vision.

    Much like the dry form of macular degeneration, a breakdown in the waste removal system may be what's causing the abnormal growth of blood vessels. When the waste from the cones and rods isn't disposed of and begins to accumulate, sufficient flow of nutrients to the macula is interrupted. The abnormal growth of blood vessels may be a response to this interruption in the flow of nutrients. The mechanism that triggers the development of new blood vessels is unclear, and it remains the subject of scientific study. Whatever the cause of the abnormal growth, the result is a disruption in the nutrition of the macula, and without enough nutrients, healthy tissue in the macula begins to deteriorate.

    With the wet form of macular degeneration, sight loss is usually rapid and severe, often deteriorating to 20/200 vision or worse, which is considered legally blind. This means that what someone with normal vision can see from 200 feet away, a person with 20/200 vision can see only from 20 feet away.

Retinal pigment epithelial detachment
Another form of wet macular degeneration, called retinal pigment epithelial detachment, occurs when fluid leaks from the choroid under the RPE even though it appears that no abnormal blood vessels have started to grow. The fluid collects under the retinal pigment epithelium, causing what looks like a blister or a bump under the macula.

This kind of macular degeneration causes similar symptoms to typical wet macular degeneration, but your vision can remain relatively stable for many months or even years before it deteriorates. Eventually, however, this form of macular degeneration usually progresses to the more common wet form of macular degeneration that includes newly growing abnormal blood vessels.

Treatment

Some treatment options are available for wet macular degeneration. But the success of the treatment — stopping further progress of the disease — depends on the location and the extent of the abnormal blood vessels, or choroidal neovascularization (CNV). The damage already caused by macular degeneration can't be reversed. The sooner CNV is detected, the better your chances of treatment preserving what's left of your central vision.

Wet macular degeneration treatments
Procedures for wet macular degeneration, all of which can be done on an outpatient basis, include:

  • Photocoagulation. In photocoagulation your doctor uses a high-energy laser beam to create small burns in areas with abnormal blood vessels. The process can seal off and destroy the CNV that has developed under your macula. It can prevent further damage to the macula and halt continued vision loss.

    Just a small percentage of people who have wet macular degeneration are candidates for this procedure. Whether it's right for you depends on the location and appearance of the CNV, the amount of blood that has leaked, and the general health of your macula. Even if photocoagulation is a viable option for you, the results can be disappointing. In the best candidates for this procedure, about half need repeat laser surgery. However, repeat laser treatment isn't always an option.

    If you noticed a dark or gray spot in or near your central vision before laser treatment, the procedure may make vision in that spot completely and permanently blank. With time you may not notice the blank spot any longer, especially when you use both eyes. And if you closely monitor your vision and have frequent follow-ups with your doctor, you may retain more sight than if you had received no treatment at all. Photocoagulation is a proven treatment for CNV when it's not located directly under the center of your macula — the area known as the fovea. However, photodynamic therapy also may be used successfully to treat CNV, even when the CNV is not located directly under the fovea.

  • Photodynamic therapy (PDT). This therapy is primarily used for treating CNV that's located directly under the fovea. The fovea lies at the center of your macula and in healthy eyes provides your sharpest vision. If conventional hot-laser surgery were used at this location, it would destroy all central vision. PDT increases your chances of preserving some of that vision. It won't bring back any of the vision you have lost, but it may halt the loss of your vision or at least slow down the rate of vision loss.

    This procedure combines a cold laser and a light-sensitizing drug called verteporfin (Visudyne) that's injected into your bloodstream. The drug concentrates in the CNV under the macula. When your doctor directs cold-laser light at the macula, the drug releases substances that theoretically close off the abnormal blood vessels without damaging the macula, and the CNV transforms into a thin scar.

    The overlying rods and cones are largely preserved, so there's a better chance that you'll preserve some of your vision with this procedure than if you had hot-laser surgery or no treatment at all. The therapy can be repeated if the CNV doesn't close or if it reopens after initial closure. After the procedure, you'll need to avoid direct sunlight and intensely bright lights until the drug wears off, about five days after treatment.

  • Macular translocation surgery. Macular translocation surgery is a treatment that can be used if the abnormal blood vessels are located directly under the fovea. To start the procedure, your surgeon detaches the retina, shifts the fovea away from the CNV and relocates it over healthy tissue. When the CNV is exposed, the surgeon can remove the CNV with tiny forceps or use a hot laser to destroy blood vessels without damaging the fovea. This surgery can be successful for preserving vision, and in some instances improving vision, if your vision loss is recent, the extent of CNV is limited and the tissue around the fovea is healthy. This surgery is not widely used.

    The newest treatment being used for macular degeneration involves use of drugs called anti-vascular endothelial growth factor (anti-VEGF) medications. These drugs help stop new CNV from growing by blocking the effects of a growth factor these blood vessels need to thrive. Anti-VEGF medications are injected directly into your eye. Some anti-VEGF agents that have been approved for use or are currently being investigated for treating macular degeneration include:

    • Macugen. Pegaptanib (Macugen) is approved for the treatment of wet macular degeneration. This drug is given as a series of injections into the vitreous fluid in the eye. It helps to prevent further vision loss by stopping the formation of new blood vessels and decreasing leakage from existing blood vessels.
    • Lucentis. Like Macugen, ranibizumab (Lucentis) is an anti-VEGF drug used to treat wet macular degeneration. It also impedes new growth of abnormal blood vessels and helps dry up leaking vessels. However, ranibizumab may be able to reverse some of the effects of macular degeneration, not just prevent further vision loss.
    • Bevacizumab (Avastin). Some doctors are prescribing this drug, which is closely related to ranibizumab, hoping that it will have effects. Bevacizumab hasn't been approved by the Food and Drug Administration (FDA) as a treatment for macular degeneration, but it has been approved as a treatment for colon and rectal cancer. That means that the use of this medication to treat macular degeneration is currently considered an off-label use of the drug. Still, some physicians are using bevacizumab injections to treat wet macular degeneration.

Dry macular degeneration treatments
There's no treatment available to reverse dry macular degeneration. But this doesn't mean you'll eventually lose all of your sight. Dry macular degeneration usually progresses slowly, and many people with this condition are able to live relatively normal, productive lives, especially if only one eye is affected.

Photocoagulation is a procedure normally used for people with the wet form of macular degeneration, but there's an ongoing study of laser photocoagulation for people who have dry macular degeneration associated with drusen.

Typically, a high-energy laser is used for this procedure, which seals off and destroys the abnormal blood vessels that develop in wet macular degeneration. Researchers hope to learn if low-intensity laser photocoagulation to the back of the retina will cause regression of the drusen and delay the onset of visual loss for people with dry macular degeneration. This national trial is called the Complications of Age-Related Macular Degeneration Prevention Trial (CAPT).

Other emerging treatments, ongoing studies
Therapies under study include:

  • Kenalog. Triamcinolone (Kenalog) is a steroid drug used to treat eye inflammation and swelling (edema). Clinical trials are under way to determine whether Kenalog injections, alone or in combination with other therapies, might improve vision in people with macular degeneration. Some ophthalmologists are using Kenalog injections in combination with photodynamic therapy, hoping to maximize the therapeutic effect of photodynamic therapy.
  • Rheophoresis. In this procedure, blood is removed from your body, filtered and then returned to your body. The idea behind this therapy is that rheopheresis may remove substances from your blood that contribute to poor blood flow in the blood vessels nourishing your retina.

There are other ongoing studies investigating the use of implantable optical devices.

Because research into new treatments for macular degeneration is ongoing, it's a good idea to visit your doctor periodically to see if a new treatment might be available.




Contents

DIABETIC RETINOPATHY article
LASIK AND PRK



Copyright © 2010 All Rights Reserved.