I mentioned in my introductory Blog that I would be writing about eye diseases. Before I do so I would like to mention again that this Blog is not intended to take the place of good medical advice. Since all medical situations are individual, it is important that you always consult your eye doctor regarding your eye condition.
The first eye disease that I would like to discuss is Age-related Macular Degeneration, also called AMD. My main reason for starting with AMD is that it is the number one cause of vision loss in Canada. More than a million Canadians have some form of AMD, with an estimated more than 250,000 having an advanced form of the disease causing significant vision loss. So what is AMD?
As the name indicates, it is a condition in which there is significant degeneration of the macula, the central region of the back part of the eye called the retina. The macula is the region of the retina where light is focused, and where it is transformed from an image into a message that is transmitted to the brain. If the macula is "smooth" the light is focused clearly and the image received by the brain is clear. If, however, there is some damage to the macula, as occurs in AMD, the light may become distorted and the image that is transmitted to the brain is no longer a clear one. Since the macula is the central part of the retina, if the image in this region becomes damaged, one will lose one's central vision first. As the damage to the macula increases, the loss of vision in the central region will expand until large areas of one's vision are affected. The macula is responsible for one's ability to see fine details such as reading or seeing the details on people's faces. It is also responsible for colour vision. For these reasons, damage to the macula can be quite debilitating and may take some time to get used to. Vision rehabilitation professionals, however, can assist people to learn techniques that permit them to view objects with their peripheral vision.
There are two types of AMD, generally referred to as Dry AMD and Wet AMD. Dry AMD is the most common form of the disease: about 85 to 90 % of AMD patients are diagnosed with Dry AMD. The development of Wet AMD is almost always preceded by Dry AMD.
Dry AMD occurs when light sensitive cells in the macula gradually break down. Often deposits known as drusen occur under the retina. These drusen are believed to be debris from deteriorating tissue and can be detected by an eye doctor during an eye examination. In the early stages of dry AMD there is a little blurring in the central part of one's vision. Later on this blurring can become quite marked and one can lose large amounts of one's central vision, however Dry AMD may take a long time to progress to serious vision loss. In fact the changes may be so gradual that one is not aware that they have the disease. For this reason, it is really important that everyone has regular eye examinations by an eye doctor, particularly if they have any of the risk factors for AMD. Every person is different, however, so some people may lose vision quickly. Others may have Dry AMD for years without losing significant vision. If you have Dry AMD it is essential that you see your eye doctor regularly in order to make sure that your disease is not getting worse.
About 10 – 15% of people with Dry AMD go on to develop Wet AMD, the more serious form of the disease. Left untreated people with Wet AMD can lose much of their vision very quickly. Studies show that most untreated Wet AMD patients can lose their functional vision in less than two years, but this loss of vision could take as little as three months. People with Wet AMD in one eye are at a much higher risk of developing Wet AMD in the other eye.
Early symptoms of Wet AMD usually involve straight lines appearing wavy and a blind spot occurring in one's central vision.
It is important to understand the risk factors for AMD so that you can take precautions that may prevent AMD or help control its progression. While it is still unclear as to what exactly causes AMD, there are a number of risk factors that are associated with the development of the disease. As the name implies, age is a risk factor for developing AMD. The older you are, the greater the likelihood you will develop the disease. Family history is another risk factor. If one of your parents, or brothers or sisters has AMD, there is a greater likelihood that you will develop the disease, and in fact there are now genetic tests available that can measure your genetic risk of developing the disease. People of Caucasian ethnic background are at higher risk of developing AMD, but clearly not every old Caucasian person will develop the disease. They are just at a higher risk than younger non-Caucasians. Smoking (both primary and second-hand smoke) has been shown to be a major risk factor for AMD. People who smoke are up to three to four times more likely to develop AMD. The good news, however, is that if you quit your risk of developing AMD returns to a level close to people who have never smoked. A poor diet, such as one rich in saturated fats and low in fresh vegetables may increase your risk of developing AMD. Leafy green vegetables contain special vitamins and anti-oxidants that have been found to be healthy for the macula. Recent studies have also shown that eating foods high in omega-3 fatty acids such as certain oily fish, can decrease one's risk for developing AMD. Lifetime exposure to the sun's harmful ultraviolet rays (both UVA and UVB) can increase the risk of developing AMD. For this reason it is recommended that one wear sunglasses whenever one is outdoors. Even when it is cloudy and there is no apparent sun, UV rays can penetrate the clouds and can affect your eyes. We also recommend that one wear a broad-brim hat when spending time outdoors. People who are obese also have a higher risk of developing AMD, so controlling your weight and your diet; quitting smoking; and wearing sunglasses are four really constructive things you can do to lower your risk of developing AMD.
In my next Blog I will discuss how your eye doctor determines that you have AMD and what some of the current treatment options are.