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AGE-RELATED MACULAR DEGENERATION

Do you have blurring or a blind spot at the center of your field of vision? Age-related macular degeneration (ARMD) could be the problem.

The macula is a small area in the center of the retina in the eye that is responsible for sharp, detailed central vision. Macular degeneration results in a gradual distortion of central vision, and sometimes leads to a central blind spot called a scotoma. When central vision is impaired, you may have difficulty recognizing faces and colors, driving a car, reading print, or doing close handwork, such as sewing or other handcrafts.

The incidence of age-related macular degeneration (ARMD) is increasing, especially in developed countries. In the USA alone, about 10-15 million individuals have this condition. It is the leading cause of low vision among older people and occurs most frequently among Caucasians.

ARMD attacks and weakens the central portion of the eye (macula) that is responsible for central vision and essential for making out fine detail. Common features of the disease are a progressive wasting of the capillaries forming the inner vascular layer of the choroid of the eye (choriocapillaris), Bruch’s membrane of the choroid, and the retinal pigment epithelium in both eyes. This results in blurred vision in the center of the eye and can also cause blind spots in your center of vision.

THERE ARE TWO MAIN TYPES OF ARMD

The most common type is dry ARMD and it also is the less severe. About 85% of the total cases of macular degeneration are dry ARMD. It is characterized by the deterioration of the tissue of the macula. Yellowish deposits called drusen form under the macula, causing it to thin and dry out. This type has a slow variable progression. Significant impairment of vision occurs in some patients over 5-10 years.

There is no known treatment that prevents advanced stages of dry ARMD or that can restore the loss of central vision. However, studies have shown that taking specific multivitamins and minerals can possibly delay intermediate ARMD from progressing to advanced stages.

The other type is the more aggressive form of the disease and is called wet (exudative) ARMD. Even though only 15% of the total macular degeneration cases are exudative, wet ARMD accounts for 90% of severe vision loss from the disease. In its advanced stages it is characterized by a rapid growth of small blood vessels beneath the retina. This process is called neovascularization and also is seen in other eye conditions, such as neovascular glaucoma. Affected blood vessels leak blood and other fluid, which form scar tissue that causes vision loss. Wet ARMD can be treated with laser surgery, photodynamic therapy, and injections in the eye, which can slow the rate of vision loss. However, recurrence of vision problems over time is common after treatment.

WHO IS AT RISK

According to the American Academy of Ophthalmology, if you have two or more of the top-five risk factors listed below, you should get a thorough eye examination by an ophthalmologist or other medical eye specialist and learn what you can do to reduce your risks.

Smoking
Obesity
Age 60 Years or older
High Blood Pressure (hypertension)
Family History of ARMD

Other reported risk factors for ARMD include:

Female sex.
Hypercholesterolemia (high blood cholesterol levels).
Previous high exposure to ultraviolet light.
Hyperopia (farsightedness).
Cataract surgery.

SIGNS OF AGE-RELATED MACULAR DEGENERATION

Common signs indicating that you might have ARMD include, seeing blurry areas on a printed page, noticing that straight lines appear wavy, and having dark spaces in your center of vision. If you are experiencing any of these you should see an ophthalmologist for an examination.

The tangent screen test or the Amsler Grid is a simple diagnostic instrument that aids in the detection of visual disturbances caused by changes in the retina, especially the macula.

Amsler Grid, revealing distortion seen by
patient with age-related macular
degeneration. Source: Khaw PT, Shah P, and
Elkington AR. ABC of Eyes, 4th Ed. London:
BMJ Publishing Group Ltd, 2004:60.

Developed in 1945, the Amsler Grid is a matrix of horizontal and vertical lines used to monitor a person's central visual field. For a visual field evaluation using an Amsler Grid, the person covers one eye and looks at the small dot in the center of the grid. The patient asked to report any distortions in the horizontal or vertical lines surrounding the central dot. The examiner then maps the distortion area on the grid and this is used to estimate the degree of central vision disturbance. The test is then repeated with the opposite eye.

Originally the Amsler grid was black and white (as shown in the figure). However, a color version with a blue and yellow grid is more sensitive and can be used to test for other visual pathway abnormalities, including glaucoma and other problems associated with the optic nerve.

Although ARMD is a very serious condition, it does not result in total blindness. With the help of a vision loss specialist, you can learn to use your side (peripheral) vision to read and perform other tasks usually performed by the central part of the eye.

REFERENCE:

Alfaro DV, Liggett PE, Mieler WF, Quiroz-Mercado H, Jager RD, and Tano Y. Age-Related Macular Degeneration: A Comprehensive Textbook. Philadelphia: Lippincott, Williams and Wilkins, 2005.