The macula is a tiny circle in the middle of the retina, a light-sensitive membrane that lines the inside of the back of the eye. In older people, it sometimes begins to deteriorate or degenerate for unknown reasons. Macular degeneration is the leading cause of legal blindness in Canada. However, macular degeneration rarely leaves you totally unable to see.
There are two types of this disease:
- Dry macular degeneration accounts for about 85% of cases. The tissue of the retina shrinks and pigments accumulate inside of it. Dry macular degeneration can progress to the wet form.
- In wet macular degeneration, new blood vessels grow around and behind the macula. There's sometimes bleeding in or behind the macula. Material seeps into the retina and settles in the macula. This is called an exudate. Eventually the exudate disappears, but a scar takes its place. All people who have wet macular degeneration had dry macular degeneration first.
The causes of macular degeneration are unknown, but the risk grows with age. Because it's extremely rare in people under age 50, the condition is usually referred to as age-related macular degeneration (AMD).
There are some known risk factors for macular degeneration. Smoking may increase your chances of developing the condition and seems to speed up its progress. High blood pressure, heart disease, sun exposure, obesity, and a diet lacking in dark green leafy vegetables and omega-3 fatty acids may also be associated with macular degeneration.
Macular degeneration runs in some families but not in all. Some studies have suggested that both genes and environment contribute to the onset of macular problems. Wet macular degeneration, at least, seems to be more common in people with poor cardiovascular health. Although it only accounts for about 15% of the cases, wet macular degeneration is responsible for 90% of the blindness caused by this disease.
Symptoms and Complications
Both types of macular degeneration are completely painless. In dry macular degeneration, the centre of the field of vision in an eye slowly blurs or grows dim. You can still see colours, but the details aren't clear. This tends to happen over a period of years. Often, people don't notice the early stages, especially if the other eye is working fine.
Unfortunately, macular degeneration rarely affects just one eye. It may take time, but the other eye may eventually start to develop the same problems.
The vision loss in wet macular degeneration is much more rapid, occurring over days to weeks. While the central part of the field of vision fades and blurs, it usually vanishes completely, leaving a large blind spot. An early sign of wet macular degeneration is when you notice that lines in the centre of the field of view become wavy. This is due to new blood vessels leaking fluid under the macula, which lifts it from its bed and deforms its shape. Wet macular degeneration usually occurs in one eye at a time.
Making the Diagnosis
An ophthalmologist or eye specialist will likely know you have macular degeneration from your description of the symptoms of whiteout, blackout, or blurring of the centre of vision, but an eye exam is needed to confirm the diagnosis.
Any eye exam involves examining the retina visually. The ophthalmologist will look into your eyes after putting in some eye drops to dilate the pupils. Tiny yellow flecks called drusen are a possible sign of macular degeneration. Some people have drusen without macular degeneration, but increasing amounts of this material may predict future problems.
Macular degeneration can be detected with a test called an Amsler grid. This is a poster showing a grid of vertical and horizontal lines with a dot in the centre. A person with macular degeneration may see wavy lines or missing areas of the grid while focusing on the dot in the centre. When wet macular degeneration is suspected after an eye exam, a fluorescein angiography is done to see the blood vessels in the eye more clearly. For this test, fluorescein (a non-toxic dye) is injected into a vein and a special light is used to see the macula.
Treatment and Prevention
While there's little that can be done for dry macular degeneration, the disease progresses very slowly, and will probably never completely black out the central vision. Many people with this condition live full lives without serious disability.
Some studies have suggested a link between poor nutrition and faster degeneration of the macula. According to this evidence, fruit and dark green vegetables like spinach can slow the disease and contribute to better outcomes. For some people, a doctor will recommend a daily supplement that contains zinc, copper, vitamin C, vitamin E, lutein and zeaxanthin, which may help reduce the risk of the advanced disease and delay vision loss. Talk to your doctor or pharmacist about which supplement is right for you.
There is no cure for wet macular degeneration, but treatment may help to slow it down. Medications injected into the eye, such as aflibercept*, bevacizumab, ranibizumab or brolucizumab may be used to slow down the growth of blood vessels. Daily supplements may also be recommended.
Laser surgery can be used to prevent growth of abnormal blood vessels that leak into the retina, but this surgery is rarely done. Photodynamic therapy may also be used. This involves injecting a medication called verteporfin into a vein. Then, a light is used to activate the medication to close abnormal blood vessels. It's been shown that bright sunlight may speed up the progress of macular degeneration. Those with the condition should consider wearing UV-protective sunglasses when they are outdoors during daytime hours.
People who have lost their vision may need magnifiers, strong reading glasses, and other devices to help them manage.
To help reduce your chances of getting macular degeneration:
- don't smoke
- eat a healthy diet rich in leafy greens
- maintain a healthy weight
- wear sunglasses with UV protection during the day