If you are reading this, it is likely that you or someone close to you has been diagnosed as having some form of macular degeneration. The following information will hopefully allow you, your family, and your friends to understand macular degeneration. It is important to know what causes macular degeneration, how it affects eye sight, and what can be done about it.
MACULAR DEGENERATION is a condition which can cause permanent loss of central vision. Though it almost never causes total blindness, it is the #1 cause of loss of vision in people over 50 in the United States. One form of macular degeneration can be treated with laser.
Before we talk more about macular degeneration, it is important to understand how the eye works when it is functioning properly. The eye is like a camera. When you take a picture, the lens in the front of the camera allows light through and focuses the light on the film that covers the back and side walls of the camera. When the light hits the film, a picture is taken. The eye works in much the same way. The front part of the eye, including the pupil, cornea, and lens, are clear and allow light to pass through them. The light also passes through a large space in the center of the eye called the vitreous cavity. The vitreous cavity is filled with a clear, gel-like substance called the vitreous or vitreous gel. The light is then focused on a thin layer of tissue called the retina. The retina is like the film in your camera, and is the seeing tissue of the eye. When the focused light hits the retina, a picture is taken. The messages about this picture are sent to the brain through the optic nerve. This is how we see.
The retina has two parts: the peripheral retina and the macula. The macula is very small and is located near the optic nerve. It comprises only 5% of the total retinal surface. The large area of the retina which surrounds the macula (and makes up 95% of the retinal surface) is called the peripheral retina. This area gives us vision to the side, or peripheral vision. Because the peripheral retina cannot see detail clearly, we cannot use peripheral vision to read, thread a needle, drive, or even recognize a face. To see fine detail, we must look straight ahead using the macula. Even though the macula is only a small part of the retina, it is 100 times more sensitive to detail than the peripheral retina. It is the macula that allows to see tiny detail, read fine print, recognize faces, thread a needle, read a watch, see street signs, etc. The only way to see detail is by using your macula, and it must be healthy to work properly.
The process of macular degeneration is often related to aging. There are some unusual types of macular degeneration which start very early in life. However, most patients with macular degeneration begin to notice problems with their eyesight some time after age fifty. Macular degeneration is also in part hereditary, and therefore often runs in families. If you have age-related macular degeneration, your blood relatives should have a retinal evaluation every year or two after age fifty.
Macular degeneration usually begins with the appearance of spots on the retina. These spots are called drusen.
The presence of drusen does not usually change vision very much. Most patients with drusen do not have serious visual loss, and only a few develop severe macular degeneration with loss of vision. When macular degeneration does lead to loss of vision, that loss usually starts in just one eye, and only later may affect the other eye. In some cases, it never affects the fellow eye. When a person loses vision due to macular degeneration in one eye, the loss of vision may not even be noticed because the healthy eye can still see detail. It is only when macular degeneration severely affects both eyes that it becomes difficult or impossible to do the kind of work that requires central vision, vision that can discern fine detail.
In general, it is important to discover any change in vision as early as possible because the chance that treatment will help is greatest in the early stages of any eye problem. That is why you should test the eyesight of each eye, each day, especially if your doctor has told you that you have drusen or early macular degeneration.
Macular degeneration almost never causes total blindness. Almost all those with severe macular degeneration in each eye can see well enough to ambulate, take care of themselves, and continue those activities which do not require detail vision. A person with severe macular degeneration who has lost the ability to see detail with either eye rarely loses peripheral vision, and will still be able to perform normal daily activities fairly well.
One very good way to test the central vision in order to detect even the smallest changes when they first appear is to use an Amsler grid. This grid is a square checkerboard with a central black spot. When staring at an Amsler grid, all the lines should appear straight and dark. However, if you notice waviness or blurriness, you should inform your eye doctor. The grid is used to check one eye at a time.
Symptoms of Macular Degeneration
In the early stages of macular degeneration, vision may become blurred for distance or reading, or for both. A very frequent and important symptom is distortion. Straight lines will not be straight; a telephone pole or door frame will seem bent, crooked or irregular. If you check your eyes with an Amsler grid, the grid will appear distorted in the affected eye, and the small boxes in the area with the problem will vary in shape and size. Also, you may see a dark gray spot similar to the aftereffect caused by a flash bulb. You may also notice the size of an object appears different in each eye or that colors do not look the same for each eye. These changes in your eyesight are important symptoms, and anyone who has these symptoms should make sure they visit their eye doctor promptly. DO NOT assume you simply need a new pair of glasses and wait for an appointment.
What is the doctor looking for?
There are two forms of macular degeneration: a dry form and a wet form. There is another uncommon form, called a pigment epithelial detachment (PED), which will be discussed later. In order to determine if you have macular degeneration, and which form of it you have, the doctor will measure your vision and examine your eyes. By looking at the retina, the doctor will be able to tell if there is an abnormality. If drusen are found, you will want to schedule regular eye checkups to make sure no further damage is occurring. It may be necessary for photographs to be taken of each macula, to use for comparison with future examinations.
Dry (atrophic) macular degeneration
Drusen are considered to be a dry form of macular degeneration. When drusen are present for a long time, the macula may become thinner and stop working. This is referred to as dry, or atrophic macular degeneration, and is often the cause of a slow and progressive loss of vision.
Some people with age-related macular degeneration note blank areas in their central vision. At this time there is no medical or surgical treatment for this form of macular degeneration. However, eyesight may be helped somewhat by the use of special low-vision lenses: magnifying lenses for close up, and telescopic lenses for distance. With counseling, people can learn to use some of their peripheral vision to help them see more clearly, and to cope more effectively with the practical tasks of everyday living. Because the dry form of macular degeneration with drusen or atrophy can change into the wet form, it is important for anyone with the dry form to monitor their central vision with the Amsler grid, and report any new changes to their doctor. The dry form occurs in 85 - 90% of people with advanced macular degeneration. The wet form, which can be even more severe, occurs in only 10 - 15% of people with advanced macular degeneration.
Wet macular degeneration (choroidal neovascular membrane - CNV)
In the wet form of macular degeneration, abnormal blood vessels grow under the retina near or within the macula, and lift the retina up, very much like the roots of a tree growing under a sidewalk. These abnormal blood vessels are called a choroidal neovascular membrane, or CNV, because they grow from the choroid, the blood vessel area under the retina.
The CNV (abnormal blood vessels) may leak fluid, bleed, and lift up the retina. When this happens, central vision is reduced and is often distorted. The longer the CNV continues to leak/bleed/grow, the more central vision will be lost. An eye with this type of macular degeneration will usually lose its ability to see detail. In some cases, prompt laser treatment may stop or minimize the loss of vision, but laser treatment does not guarantee that vision will not be lost. In addition, if the CNV occurs in one eye, there is a 10% chance per year that it will occur in the other eye. The earlier the CNV is discovered, the more likely it is that some or much of the central detail can be preserved. The later it is discovered, the less likely laser treatment can be done. In other words: Pay close attention to your eyesight, and see your eye doctor promptly if there is any type of change in your vision.
The only treatment proven effective and beneficial for CNV is laser therapy; there is no medication or other surgical treatment proven to be of benefit for either atrophic (dry) or CNV (wet) macular degeneration. One drug, interferon, has not been shown to be of any benefit for CNV. Recent studies with low-dose radiation treatment have also shown no improvement for CNV. Microelectric current treatment (rheotherapy) has not been shown as beneficial for either form of macular degeneration. Many other drugs and agents are currently under consideration, but to date there is no scientific evidence of their value. These will be discussed later.
The National Eye Institute is presently sponsoring the AREDS, which is testing the use of antioxidants and zinc on the progression of age-related macular degeneration. However, again, no vitamin, mineral, drug, or other agent has been proven to be useful in slowing or stopping the progression of wet or dry macular degeneration.
Pigment epithelial detachment
There is a third form of macular degeneration, called a pigment epithelial detachment, or PED.
In this form of macular degeneration, a blister, or PED, can form in the macula, causing blurring or distortion of vision. Laser treatment may be recommended if CNV (abnormal blood vessels) can be identified. If you have a PED, you will want to have your eyes examined regularly to see if a treatable CNV develops.
If your doctor diagnoses an abnormality and suspects CNV, the wet form of macular degeneration, a special test called a fluorescein angiogram will be done. This is necessary if the doctor thinks the laser treatment may help. For this test, dye (fluorescein) is injected into a vein in your arm, and as dye travels throughout the body, it allows the doctor to take photos of the retinal circulation using a special camera (this is not an x-ray). The series of photographs taken during this test will identify the CNV, and provide the doctor with a type of map which can be used during laser treatment. It can also show the doctor if the CNV is under the macula (the foveal center), and therefore is untreatable with laser. Fluorescein angiography is repeated a few times in the weeks following laser treatment to be sure the laser has destroyed the CNV.
In some patients, the CNV cannot be identified clearly with fluorescein angiography. To help detect the CNV in such cases, a new test called indocyanine-green choroidal angiography (ICG) has been developed, and is being tested in a number of centers. Recent studies show that ICG angiography may demonstrate a treatable CNV in some patients thought to be untreatable by fluorescein angiography.
Laser treatment for macular degeneration
In some cases, laser treatment may be done to prevent or lessen severe loss of vision - if the CNV is discovered early enough. The laser beam is high-energy light which turns to heat when it hits the part of the retina requiring treatment. This heat destroys the CNV and stops it from growing, leaking, or bleeding. A scar forms as the result of the treatment, and this scar creates a permanent blind spot in the field of vision.
Vision does not usually improve after laser treatment and in some cases may even be somewhat worse. However, loss of vision following laser therapy, though immediate, is usually less severe than the eventual loss of vision likely to occur if no laser treatment is performed. In many cases, the visual distortion will disappear after laser treatment. This type of treatment is only effective about 50% of the time. Since macular degeneration is a condition caused by the aging process, laser treatment is often only a means of temporarily preventing further visual loss, or lessening the amount of visual loss that usually occurs if no laser treatment is done. Vision may continue to worsen in spite of laser treatment, but if laser is indicated, chances are there will be less visual loss with laser than without. If no laser treatment is applied, loss of central vision will continue. The decision about using this type of therapy depends upon the appearance and location of the CNV, as well as the amount of blood present. In addition, the general health of the macula is an important factor. In some cases, laser treatment may not be helpful or even possible, and it is best not to do it. Even if laser is considered successful and the CNV has been destroyed, newer additional abnormal blood vessels may appear months or years later and further damage the vision. The patient who is treated with laser should continually check the vision in the treated eye, and tell the doctor immediately if new changes are noted, such as a return of distortion or blurriness. Additional laser treatment may be helpful in some cases. The patient who has had laser treatment which has remained successful must use the Amsler grid every day for the rest of his or her life, and if there is a change, they must tell their eye doctor promptly.
Due to the increasing frequency of macular degeneration as the population ages, and to the millions of people affected by the wet form of the disease who are not treatable with conventional laser therapy, experimental modalities for treatment of wet macular degeneration have been tried. The first of these was submacular surgery, an operation performed to remove the vitreous gel (a procedure called a vitrectomy). A small incision is made in the retina, and the retina is elevated and the abnormal blood vessel membrane is pulled out from under the retina through a small hole. A gas bubble is then placed in the eye, and the patient is instructed to remain in a face-down position. Although initial results were promising, recent studies involving a greater number of patients show that submacular surgery for age-related macular degeneration rarely affords a significant benefit. In other conditions in which CNV occurs (such as myopia, trauma, and presumed ocular histoplasmosis syndrome), sub-macular surgery does appear to be beneficial when the CNV has gone under the center into the subfoveal space (into the center of vision).
Recently, photodynamic therapy (PDT) has been tried for the treatment of CNV once it is under the foveal center (the center of the macula). This therapy is different from conventional laser in that a dye is injected into the vein which binds to the abnormal blood vessel(s). An infrared laser beam is then used to activate the dye, causing a chemical reaction which destroys the CNV. The difference between this and conventional laser therapy is that due to the wavelength of laser light, the overlying retina is spared. Results of both studies using PDT, which are currently ongoing, have been very promising.
Lastly, recent surgical advances have allowed vitreoretinal surgeons to relocate the macular area over a healthy area of retinal pigment epithelium and choroid. This procedure is called macular translocation. A variety of different surgical procedures are being tested; however, they are all similar in one way: In the operation, either a large or small retinal detachment is created, and the macula is rotated away from the abnormal blood vessel(s) beneath it. This places the abnormal blood vessels in an area where laser treatment can be used to destroy them. Now that the macula is overlying a healthy stratum of RPE and choroid, visual function is allowed to return. Some of these procedures allow large movements of the retina, while others allow only small movements. The original operation, pioneered by Dr. Robert Machemer at Duke University, allows a large rotation of the retina, but is difficult and time-consuming, and also carries a high risk of retinal re-detachment and loss of sight. A modified or limited macular translocation procedure using a partial eye wall resection, pioneered by Dr. Eugene DeJuan at Wilmer Eye Institute, allows for smaller movements of the macula away from the abnormal blood vessels, but also appears to be safe. These surgical procedures have only been performed in a small number of patients, with only limited success. However, further study is warranted.
Macular degeneration affects millions of Americans. The vast majority of affected patients are currently untreatable. Hopefully with further advances in surgery and biotechnology, as well as a greater understanding of how the disease occurs and how it can be prevented, future generations will be spared the visual debilitation caused by this common disease.