The Hanneken Lab

Macular Degeneration: Clinical Signs and Risk Factors

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Clinical Signs and Risk Factors:  Age-related macular degeneration is the leading cause of blindness in patients over the age of 55 in the United States and other developed countries..  One out of three people over the age of 75 suffers from macular degeneration and the number of cases is expected to double in the future as the population over 65 increases.

Macular degeneration affects the portion of the eye that is known as the macula.  The macula is part of the retina, which is the eye’s inner lining, that absorbs and processes light.  The retina is similar to the film that is used to take pictures with a camera.  The macula is the area around the central part of the retina that we use for fine focusing and for reading.  Macular degeneration is caused by progressive deterioration of a region that nourishes the retina, known as the retinal pigment epithelium (RPE), which leads to degeneration of a portion of the retina itself. As a result of the damage which occurs in this region, patients have difficulty with their central vision which makes reading and central focusing difficult or impossible. Fortunately, peripheral vision frequently remains intact, and patients rarely lose all vision.

The early features of macular degeneration consist of small yellow deposits, known as drusen, which build up under the RPE cells, which nourish the retina.  These are photographs of the retina taken during an eye examination which show the normal appearance of the retina, on the left, and the hallmark signs of drusen within the macula on the right. Drusen have been shown to consist of protein deposits, modified by oxidative stress. During early stages, these deposits do not cause any symptoms and therefore cannot be detected by patients.  They can only be diagnosed by a careful eye examination.

As the condition progresses, the retinal pigment epithelial cells which nourish the retina begin to degenerate. In layman’s terms, this leads to a condition known as the ‘dry form’ of macular degeneration, which is recognized by pictures such as this, which shows the loss of the normal RPE cells in the picture on the right. This accounts for up to 90% of the cases of macular degeneration. In most cases, the degeneration occurs at a very slow rate and central vision is maintained for years.

However, in 10% of the cases, there may be a sudden change in vision with marked distortion and wavy lines.  This signals the development of abnormal blood vessels which grow under the retina around the retinal pigment epithelial cells, which nourish the retina.  In layman’s terms, these cases are referred to as the ‘wet form’ of macular degeneration and are recognized by pictures such as this, which shows blood and scar tissue that has accumulated under the retina.

A number of risk factors have been identified from large epidemiologic studies.  Many of the greatest risk factors are identical to the risk factors associated with cardiovascular disease, which leads one to speculate that if you can identify compounds which protect against the type of injury which occurs in macular degeneration, there is a good possibility that these compounds might protect against cardiovascular disease as well.  The highest risk factors are smoking, hypertension, elevated cholesterol, increased body mass and advancing age.  There is a genetic predisposition toward macular degeneration. Females and Caucasians are at increased risk, whereas, patients with darker skin tones are at significantly lower risk.  Some other risk factors include light iris color and sunlight exposure.