AMD – A Leading Cause of Blindness

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In industrialized countries, age-related macular degeneration (AMD) is the leading cause of blindness in adults older than 60 years of age. The estimated global prevalence of AMD is 8.7%, and in 2020, it was estimated that more than 190 million persons worldwide and more than 11 million persons here in the U.S. had AMD. Increasing age is the strongest risk factor, and given the exponential growth of the aging population, it is estimated that the global prevalence of AMD will increase to 288 million persons by 2040.

Numerous studies have linked smoking, uncontrolled hypertension, and a BMI over 25 to more severe AMD. Genetic factors are also important, and mutations in at least 30 genes have been reported to be associated with a risk of AMD. Early on, AMD may be asymptomatic, and is often discovered on routine eye exam. Symptoms include blurred or decreased vision in one or both eyes, distortion, blind spots (scotomas) in or around the area of central vision, and difficulty with visual function and daily activities such as reading and driving, especially in poorly lit settings. AMD primarily affects the macula, which is the cone photo-receptor rich central part of the retina. AMD is initially characterized by focal or diffuse fatty deposits called drusen, which form underneath the retinal pigment layer. Depending on the area and size of the drusen, AMD is classified as early or intermediate.

Longitudinal data from the first and second Age-Related Eye Disease Studies (AREDS and AREDS2) showed that intermediate AMD can progress to advanced disease. Advanced AMD is classified either as neovascular (or “wet”) or atrophic (or “advanced dry”). Neovascular AMD is characterized by the proliferation of new blood vessels under the retina while atrophic AMD is characterized by the atrophy, or wasting away, of the retinal pigment layer. These studies showed that without treatment AMD progresses relentlessly. AREDS evaluated the use of once-daily formulations of vitamin C, zinc, vitamin E, copper, and beta carotene and found that those study participants assigned to the micronutrient supplementation group had less disease progression. AREDS2 followed the first study but substituted lutein and zeaxanthin for beta carotene because smokers who take beta carotene have a much greater risk of developing lung cancer. Lifestyle modifications are also helpful at halting disease progression and include smoking cessation, control of hypertension, and weight loss for overweight persons.

Recently, therapies that target vascular endothelial growth factor (VEGF) have shown promise in halting the progression of neovascular AMD. These therapies, also used in cancer chemotherapy, include bevacizumab (Avastin), ranibizumab (Lucentis), aflibercept (Eylea and Zaltrap), and brolucizumab (Beovu). The American Academy of Ophthalmology (AAO) has published guidelines regarding the frequency of eye exams according to risk stratification that includes AMD. This can be found at www.aao.org/clinical-statement/frequency-of-ocular-examinations. They also have guidelines for the diagnosis and treatment of AMD at www.aao.org/eye-health/diseases/amd-macular-degeneration. Genetic testing is not recommended because there are currently no gene therapies available.

Because AMD can have no symptoms early on, if you are over 60 it is important to get regular eye exams. Speak to your eye doctor about getting regular exams.

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 By Peter Galvin, MD

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