Age-Related Macular Degeneration: Risk Factors and Treatment

The macula is the central region on the retina within our eyes where the image of what we see falls directly. With increasing age this region can undergo damage with deterioration in vision and this condition is called age-related macular degeneration (AMD). This is the most common cause of blindness in adults in developed countries with the prevalence increasing with age to 13.1% in those aged between 75 to 84.

Risk Factors for AMD

• Age – Increased incidence is noted over 65 years of age
• Ethnicity – People of Caucasian descent appear to develop AMD more than others
• Family history
• Smoking – There is a very strong association between smoking and AMD and also leads to rapid progression of the disease with increased chance of involving both eyes
• Alcohol use
• Diet low in fruits and vegetables

Types of AMD

There are two types of AMD with distinct clinical features and treatment options. These are as follows:

• Dry AMD: This is the more common type of AMD affecting 85 to 90% of people with AMD, causing atrophy or degeneration of the macula with deposition of a material termed drusen. This deposition damages the retina over time. It causes a gradual loss of vision.
• Wet AMD: This is called so as it is marked by increased formation of blood vessels in the retina which grow towards and into the macula. These vessels destroy the macula by leaking fluid into it and under the retina. The increased blood vessel formation is thought to be from excess of Vascular Endothelial Growth Factor (VEGF) which is responsible for growth of vessels in the body. Wet AMD can quickly progress to damage both eyes. This is less common, affecting 10 to 15%.

Symptoms of AMD

The symptoms of AMD differ based on the type

• Dry AMD: Individuals experience gradual loss of vision in one or both eyes. They have difficulty seeing clearly while reading or driving. They may experience blind spots or require brighter light to see clearly
• Wet AMD: This presents with sudden deterioration in vision. In addition, they perceive edges and lines to be curved, a condition called metamorphopsia.

Diagnosis of AMD

The diagnosis is suspected in any elderly individual experiencing vision loss. The following tests are performed for diagnosis

• Direct and indirect ophthalmoscopy: This is the examination of the retina by an eye doctor to look for any abnormalities
• Fluorescein dye angiography: this is a test where a dye is injected into a vein in the arm, and color photographs of the retina are captured. Newly formed retinal vessels in wet AMD leak this dye which is demonstrated in the photos
• Optical Coherence Tomography (OCT): This is an imaging study to look at a cross-section of the retina and can identify the presence of fluid in its layers.

Treatment of AMD

Treatment for both Dry and Wet AMD

• Antioxidant vitamins and Zinc: This is based on the results of the Age-related Eye Disease Study (AREDS) trial which showed benefit of vitamin and mineral supplements in individuals with both dry and wet AMD. It is important to consult a physician before starting these formulations as there are some risks of lung cancer in smokers.
• Smoking cessation: quitting smoking can slow the progression of AMD

Treatment for Wet AMD

• Laser Surgery: The abnormal blood vessels in the retina are destroyed using lasers within the eye
• Photodynamic therapy: In this treatment, a medicine is injected into the bloodstream which attaches to the abnormal blood vessels. A light is shown into the eye which upon encountering the medicine, destroys the abnormal vessels
• VEGF inhibitors: These are medicines which are injected directly into the eye which inhibit the action of the vessel producing substance called VEGF.

Prevention of AMD

• Diet: A diet rich in fruits and vegetables along with fish and nuts is encouraged
• Physical exercise: Studies have shown that exercising has a protective effect
• Avoiding smoking and quitting if currently smoking: this decreases the risk of both dry and wet AMD

References:

• What Is Macular Degeneration? [Internet]. American Academy of Ophthalmology. 2018 [cited 2018 Jul 5].
• Facts About Age-Related Macular Degeneration | National Eye Institute [Internet]. [cited 2018 Jul 5].