JULIA A. HALLER, MD
MACULAR DEGENERATION (AMD)
WHAT IS AGE-RELATED MACULAR DEGENERATION (AMD)?
Age-related macular degeneration (AMD) is a common condition affecting people age 50 years and older that is associated with central vision loss, which affects one's ability to read, drive, or see someone’s face if it progresses to more advanced stages.
The macula refers to the central portion of the retina. The retina is similar to the film inside a camera. The image one sees is focused by the cornea and lens of the eye onto the center of the retina (macula.) Many people with AMD have minimal visual symptoms and may retain good vision indefinitely. A relatively small percentage of people with AMD will lose central vision, which may impair their ability to read and drive a car.
CAUSES AND ASSOCIATIONS OF AGE-RELATED MACULAR DEGENERATION
AMD is a complex, degenerative condition that becomes increasingly prevalent with advanced age. It is typically found in people ages 50 years or more, although drusen sometimes can be seen in younger people. Family history is another important association, although simply having a blood relative with AMD does not necessarily mean or guarantee that one will definitely develop AMD. Other risk factors for AMD may be modifiable or controllable, including smoking, poor nutritional intake, and high blood pressure.
MACULAR DEGENERATION SYMPTOMS
Many people with mild dry AMD have little to no visual symptoms. Some people, however, will experience some side effects, including:
- Requiring more light to read
- Difficulty adjusting between dark and light conditions
- Mild blurring of vision
Occasionally, significant loss of central vision can occur as well. Vision loss associated with dry AMD is usually gradual or slow. Because AMD affects the macula, the symptoms are typically related to central vision tasks such as reading or driving. Peripheral vision is typically not affected. Those with wet AMD often have more pronounced symptoms, including:
- Rapidly progressing loss of central vision, typically over days to weeks
- Visual distortion
Occasionally, people may not be aware of these visual changes because their other eye sees well. Therefore, it is important to test vision in each eye separately by covering one eye at a time when checking vision.
Most people with AMD will retain good central vision and the ability to read in their lifetime. This is because 90% of people have dry AMD. This is often associated with a more favorable prognosis compared to wet AMD, though dry AMD may also gradually progress to an advanced form with atrophy of the macula, limiting central vision. People with wet AMD will quickly suffer central vision loss if left untreated. While patients may progress to legal blindness, it is important to realize that AMD affects central vision - it typically does not lead to total loss of vision. Thankfully, there are new treatments available for those with wet AMD.
Meet Wills Eye Retina Specialists
JULIA A. HALLER, MD
CARL D. REGILLO, MD, FACS
Chief, Retina Service
ARUNAN SIVALINGAM, MD
Co-Director, Retina Service
Director, Retina Fellowship
DAVID H. FISCHER, MD
Co-Director, Retina Service
ALLEN C. HO, MD
Director, Retina Research
RICHARD S. KAISER, MD
Co-Director, Retina Fellowship
SUNIR J. GARG, MD
Co-Director, Retina Research
JASON HSU, MD
Co-Director, Retina Research
JAMES P. DUNN, MD
Director, Uveitis Unit
JONATHAN BELMONT, MD
ALLEN CHIANG, MD
MICHAEL N. COHEN, MD
MITCHELL S. FINEMAN, MD
OMESH P. GUPTA, MD
M. ALI, KHAN, MD
ROBERT C. KLEINER, MD, FACS
MICHAEL KLUFAS, MD
AJAY KURIYAN, MD
SONIA MEHTA, MD
CARL PARK, MD
MARC J. SPIRN, MD
JAMES F. VANDER, MD
YOSHIHIRO YONEKAWA, MD
The Two Types of AMD
There are two major types of AMD, a "dry" (non-neovascular) and a "wet" (neovascular) form.
----- Dry AMD -----
Dry AMD affects about 90 percent of all people with macular degeneration and is characterized by drusen.
Drusen are small yellow deposits that are visible to the doctor on clinical examination of the macula and are the hallmark of AMD. Most people with drusen alone do not have significant visual changes or vision loss. A minority of people with dry AMD will advance to central vision loss due to geographic atrophy, which involves the loss of pigmented cells beneath the macula (these pigmented cells normally act to support and nourish the photoreceptor cells). There is currently no treatment or cure for geographic atrophy, though investigative research is ongoing.
There is no treatment available yet that can either halt the progression or recover vision loss from dry AMD. However, the Age Related Eye Disease Study (AREDS), sponsored by the National Eye Institute (NEI) of the National Institutes of Health (NIH), showed that a specific formulation of antioxidant vitamins and minerals had a clinically proven benefit in reducing the risk of progression of dry AMD to more advanced stages and associated vision loss by 25%. In May of 2013, the NEI proposed a modification to the original AREDS formula based on the AREDS2 study, which was an update to the original AREDS clinical trial.
----- Wet AMD -----
Wet AMD affects only about 10 percent of people with macular degeneration, yet accounts for the majority of central vision loss due to AMD.
The word "wet" implies leakage and bleeding in the macula due to abnormal blood vessels (choroidal neovascularization) that may develop spontaneously in AMD. If left untreated, these abnormal blood vessels result in permanent scarring of macular tissue and severe central vision loss. While there is still no cure for wet AMD, we currently have a few medications that are very effective in treating this condition.
In that past, laser-based therapies were used to target the abnormal blood vessels that cause wet AMD. However, the laser burns typically resulted in scarring and damage to central vision. Fortunately, there are now anti-vascular endothelial growth factor (anti-VEGF) medications available for the treatment of wet AMD. These medications, injected into the eye as an office-based procedure, are currently the preferred therapy for wet AMD due to their unprecedented efficacy. They represent the first therapy that has ever been clinically proven to help improve vision in a substantial proportion of patients with wet AMD. Timing is important, as earlier identification and treatment of wet AMD is associated with better visual outcomes.
GENETICS AND AMD
Genetics plays a key role in AMD, with heredity representing over 70% of the risk of developing the disease.
Genetic markers have recently been identified that strongly influence the risk of progression to advanced AMD with vision loss. Several of these gene variants promote inflammation by altering activation of the complement cascade, which is an active part of our immune system. Other gene variants affect mitochondrial function and increase oxidative stress in the retina, consistent with both the role of smoking as a risk factor and the benefit of antioxidants in delaying disease progression. Cholesterol metabolizing enzyme variants are also associated with this disease, consistent with the known biochemical composition of drusen.
Early identification of higher risk patients may help prevent vision loss or slow down disease progression. Environmental risk factors can be identified, lifestyle modifications can be made, and nutritional supplementation can be instituted in these situations to further reduce risk of disease progression. Frequent monitoring of these individuals may result in early detection of wet AMD, leading to better visual outcomes through earlier treatment.
In addition to a dilated retinal examination and digital color photography, various retinal imaging tests may be utilized to further assess the AMD.
This office-based test can aid in determining the extent of macular degeneration and distinguishing between dry and wet AMD. Fluorescein angiography is performed by injecting sodium fluorescein dye into a peripheral vein in the arm with a small needle. This dye travels through the blood vessels of the body and eyes. Choroidal neovascularization in the macula can be visualized as a leaking blood vessel complex under the retina. It is regarded as a safe test, but people should expect some temporary and mild yellowish discoloration of the skin and urine. Most people have no difficulty with this testing, although a small percentage of people will experience some transient nausea. Any angiogram test, however, can rarely be associated with allergic or even more severe reactions, and therefore this test is typically reserved for people in whom wet AMD is noted or suspected.
OCT is a non-invasive, office-based imaging test that uses a special light to scan the macula and determine whether there is fluid in the macula, potentially signifying wet AMD. It is commonly used in combination with fluorescein angiography to help diagnose wet AMD and is also used to monitor the response to treatment for wet AMD. There are no side effects or risks involved with OCT; there is no radiation involved.
Autofluorescence is another non-invasive imaging test is useful for evaluating the health of the pigmented cell layer beneath the macula in those who have dry AMD. The pigmented cell layer plays an important role in sustaining the health and function of retinal photoreceptor cells. Specifically, it is used to identify and track progression of geographic atrophy, which involves the loss of this pigmented cell layer and in turn, the loss of photoreceptor cells.