Macular Degeneration

Macular degeneration is an eye disease that usually strikes older adults. It affects more than one million Canadians and is the leading cause of vision loss in the elderly.

The inside of the eye is lined with a light-sensitive membrane called the retina. The retina consists of specialized cells that detect colour and contrast. The macula is a small area at the centre of the retina responsible for central vision and fine detail vision. As its name implies, macular degeneration involves the deterioration of the macula. This leads to blurred central vision and can make certain activities such as reading and driving impossible. Although the disease can severely damage vision, it rarely leads to complete blindness since it does not affect peripheral vision (around the center). Persons with macular degeneration could, for example, see the numbers on a clock, but would be unable to distinguish the hands.

There are two forms of macular degeneration:

• Dry macular degeneration is the most common form and accounts for 80 to 90% of all cases. The loss of central vision is gradual and occurs over several years. It is often the result of a thinning of the macula or pigment deposits (coloration) on the macula.

• Although less common, wet macular degeneration is characterized by the sudden and severe loss of central vision. In this case, abnormal blood vessels develop under the macula. The vessels then leak fluid or blood which partially destroys the light-sensitive cells in the macula. The macula can heal itself but scar tissue forms on the macula creating a black spot or "blind spot".

Persons at Risk

Macular degeneration is associated with the normal aging process. That being said, any person over the age of 50 years, particularly women, are "at risk". Other risk factors include family history of macular degeneration, diabetes, high blood cholesterol, hypertension, eye disease and smoking.

Symptoms

The symptoms associated with macular degeneration are limited to vision. Initially, the disease only affects one eye. This can delay diagnosis since the healthy eye generally compensates for the loss of vision in the affected eye. This can go on for several years before both eyes are finally affected. There is no pain associated with macular degeneration. The most common symptoms are:

• blurred, washed out central vision
• drop in sharpness
• reduced colour perception
• blind spot or black spot in the centre of the visual field
• difficulty seeing far straight lines that look wavy or distorted (wet form)

Diagnosis

It is recommended that all those over 50 years of age go for an eye examination at least once every two years. Screening for macular degeneration can be done by an optometrist or an ophthalmologist. If detected early, it is possible to slow the progress of the disease and even stop it in the case of the wet form of the disease.

Two tests are commonly used to diagnose macular degeneration. The first one, known as the Amsler grid, is used to assess whether straight lines are distorted and if there is a blind spot or black spots in the field of vision. This test can also be used for follow-up purposes (see Amsler Grid published by Vigilance Santé). The second test is an examination called ophthalmoscopy. This test involves the use of eye drops to dilate the pupil which allows the specialist to examine the interior of the eye.

Treatment

There is currently no treatment available to restore lost visual acuity (sensitivity). Medications may be taken to slow the progress of macular degeneration. Taking certain vitamins and minerals also seems to slow the progression of the disease. Additionally, laser surgery can stop the progression of wet macular degeneration. Otherwise, individuals with this eye disease must learn to live with limited vision. There are vision rehabilitation clinics specialized in helping those with macular degeneration learn how to live with low vision and remain independent. To find a clinic near you, contact the Canadian National Institute for the Blind (CNIB).

For more information or for support:

• The Information Service of the Canadian Ophthalmological Society
• Canadian National Institute for the Blind (CNIB)