AMD: The Sneak Thief of Vision
Age-Related Macular Degeneration (AMD) is considered to be the leading cause of functional vision loss in people over the age of 55 in the western world. Estimates of how many people are affected vary considerably, but the percentage of the population with it increases with age. While only 2% of people aged 50 to 59 have the disease, the incidence rises to nearly 30% by the age of 75 years. Therefore, the greatest risk factor for developing this condition is age.
There is important new information regarding macular degeneration, genetics, and ocular vitamin supplements that patients should understand; please read more about these recent developments here.
Additionally, certain medications, high blood pressure, smoking, overexposure to ultraviolet light, heart disease and obesity have also been implicated. The most important new finding about macular degeneration is that it has a strong hereditary component; race and gender have been shown as factors as well, with whites and females being more at risk than others.
AMD affects the central vision of the eye, the part which sees color and fine detail, so it can have a devastating effect on everyday activities such as reading, driving or even recognizing other people’s faces. It is irreversible and progressive over time. It is a sneaky thief as well, because it usually begins in one eye before the other, so people who are using both eyes may not notice the vision loss until they have a routine eye examination.
There are two main types of AMD, known as “dry AMD” (also known as atrophic ) and “wet AMD,” (or exudative). About 80% of patients with AMD have the dry, atrophic type, which is characterized by thinning of the retina in the macular area, and which progresses slowly. About 20% of those with dry AMD will progress to having the wet, exudative type, which is faster to progress and can have worse outcomes.
“Wet” AMD, is more serious, but also more treatable. The circulation in the blood vessels inside the eye are compromised, so the body sends out Vascular Endothelial Growth Factor (VEGF), which triggers the growth of new and very fragile blood vessels, which can then break open and release fluid and blood into the retina, lifting it and changing the tissue, which causes the disruption of vision. Patients will notice distortion of reading material or other fine details, and may notice that colours are not as bright or clear. As fluid builds up under the central part of the retina, the vision worsens, and may result in permanent scar tissue formation.
Treatment and Prevention of AMD
Preservation of functional vision is the best course of action, but there is only a short period of time in which to act for greatest effect. A large study of macular degeneration over long time periods which took place in multiple vision clinics, called AREDS, (which stands for “Age-Related Eye Disease Study”) showed a strong relationship between the shortness of delay before treatment and successful visual preservation. This delay is significant even in terms of weeks; the study found that about half of those who were treated for wet AMD in the first eye failed to maintain near normal vision, but were successful in preserving vision about 90% of the time in the second eye. The difference in outcomes is thought to be the result of better monitoring of vision in the second eye, once the first was diagnosed with macular degeneration.
There are several treatment strategies for AMD at this time, a vast improvement over the situation only a few years ago. For the dry, atrophic type, emphasis is on prevention of vision loss, with frequent eye examinations and a healthy diet being the best overall strategy. People who are 55 or over should have a thorough vision and eye examination at least once each year; if there is a family history of macular degeneration, the eyecare practitioner may hand the patient a simple take-home card printed with crisscrossing lines called an Amsler Grid. The patient is usually instructed to monitor their vision about twice a month (not more frequently, as changes are gradual and may not be noticed if done more often), to check for any loss of clarity in the central part of the grid, or any distortion or change in the appearance of the lines.
The most recent and important breakthrough in the prevention and treatment of macular degeneration involves the use of DNA testing to determine whether the AREDS Formulation alone, the AREDS Formulation with zinc added, zinc supplements alone, or, in some cases, no supplementation at all, will be the most helpful for an individual patient. For information about this specific issue, please see the article discussing macular degeneration, genetics and vitamin supplements.
If dry AMD is progressing into the wet form, doctors can inject medications known as anti-VEGFs, into the eye, which have the effect of inhibiting the growth of those new blood vessels. These drugs can slow progression of wet AMD significantly, and may be considered as part of an ongoing management program. There are four different anti-VEGFs available. Depending on what medication is being used, injections should be repeated as often as every month or every two months.
Another strategy is the use of a low-power laser used with a drug called Visudyne, which is injected in the patient’s arm. Once the circulatory system carries the Visudyne into the eye, it collects in the areas of new blood vessel growth and seepage, and makes those tissues more reactive to the laser, sealing them off. This treatment is still used in concert with anti-VEGF medications.
Ocular vitamin supplements can be a very useful addition to any prevention strategy, but it is important to understand how specific formulations may interact with individual genetics before beginning any use of them.
Other Helpful Strategies
Once vision has been lost to macular degeneration, there is no treatment that will restore it, making prevention of vision loss of paramount importance. However, even when vision has been lost, there are techniques that patients may find helpful in daily living. Macular degeneration does affect the central part of the vision, but it does not affect the peripheral vision and does not result in complete blindness, so patients may find their daily living activities are improved with the use of magnifying lenses, better and brighter lighting, large print books, and specialized clocks and telephones. Some low vision aids use prisms to shift images from the central to the peripheral retina so that they may be seen more easily.
Financial institutions can also provide raised-printing checks to make it easier for people to manage their own finances.
Other low vision services, such as orientation and mobility training, audio books, high-tech aid assessments, occupational and physical therapy and computer assessments are available from the Canadian National Institute for the Blind (CNIB). More information about services and devices is available from your eyecare practitioner.
Above is shown a representation of what a person with advanced macular degeneration may observe. Next to it is shown an Amsler Grid, undistorted, as it would appear to someone with normal vision; next to it is a representation of the distortion or waviness of the grid lines that may appear with macular degeneration.
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