Age-Related Macular Degeneration

The human retina is made up of layers of cells that line the entire inside of the globe of the eye. The macula is the most sensitive part of the retina, located in the center. The macula is about the size of the head of a straight pin, and contains millions of light-sensing cells that provide sharp, detailed, “straight-ahead” central vision. When light strikes the back of the eye, the cells of the macula and the rest of the retina send electrical signals to the brain through the optic nerve. The brain translates the electrical signals into the images we see.  When macula cells are damaged or destroyed, the images received by the brain are distorted.

• Age-related macular degeneration (AMD) is a progressive eye condition affecting as many as 15 million Americans and millions more around the world. There is no cure for AMD, which destroys the clear central vision necessary for reading, driving, identifying faces, watching television, safely navigating stairs and performing other daily tasks we take for granted. It can make it more difficult to see contrast and can change the way color is seen. Peripheral vision may not be affected, and it is possible to see “out of the corner of your eye.”
• AMD is the number one cause of severe vision loss and legal blindness in adults over 60 in the U.S. It escalates with age.  More than one senior in three over the age of 75 is likely to develop signs of AMD, with over 200,000 new cases diagnosed every year.
• There are two types of AMD – atrophic or “dry AMD" and neovascular or “wet AMD”.  All AMD starts in the dry form. There are treatments available for wet AMD to stop disease progression, and research is underway to find an effective treatment to limit the vision loss that occurs with dry AMD. Even with vision loss resulting from AMD, training and special devices can promote independence and a return to favorite activities.

There are some things you can do to reduce the risk of AMD. Research with large populations around the world has revealed a list of lifestyle factors that can be changed. Other things that contribute to AMD include your family history and age. While you can’t control these risk factors, it’s important to know about them.  

Things You Can’t Change

• Age – AMD signs are present in about 14% of people 55–64; 20% of those age 65–75; and up to 40% of individuals over age 75.
• Gender – AMD is more common in women than in men.
• Race – AMD is more common in Caucasians than other races, but it exists in every ethnicity.
• Eye Color – AMD is more common in people with blue eyes.
• AMD in One Eye – If you have AMD in one eye, your chance of developing it in the other eye is higher. Dry AMD in one eye may predispose you to wet AMD in the other eye.
• Genetics – If others in your family have AMD, you have a greater risk of developing it.

Risk Factors You Can Change

• Smoking – Smoking increases your risk, especially if AMD runs in your family.
• Diet – A poor diet, low in antioxidants and high in saturated fats and processed foods may increase your risk of developing AMD.
• Obesity – People who are very overweight have a higher risk of AMD.
• Exercise – A sedentary lifestyle contributes to AMD.
• Cholesterol – High cholesterol is bad for your eyes and your heart.
• Blood Pressure – High blood pressure may be involved in AMD.
• Sun Exposure – Ultraviolet and blue light from the sun and electronics can damage the retina.

Dry AMD is the most common type of macular degeneration and affects 85-90% of people who have the condition. In the dry form, there is a breakdown or thinning of the layer of retinal pigment epithelium (RPE) in the macula. These RPE cells support the light-sensitive photoreceptor cells that are critical to vision. When we look at something, photoreceptor cells (rods and cones) in the retina gather the images and send them to the brain, where vision information is processed.

Dry AMD is characterized by the presence of drusen and thinning of the macula. Dry AMD reduces central vision and can affect color perception. Generally, the damage caused by the dry form is not as rapid as that of wet AMD. However, over time, it can cause profound vision loss. The degeneration or death of these cells is called atrophy. Hence, dry AMD is often referred to as atrophic AMD. The more advanced stage of dry AMD is called geographic atrophy, where entire patches of photoreceptor cells die leaving dark grayish patches in the central vision.

Drusen are tiny yellow or white protein deposits in a layer of the retina called Bruchs membrane. They are the most common early sign of dry AMD. They may be the result of a failure of the blood vessels to dispose of waste products produced by retinal cells. 

There are several types of drusen with different levels of risk. Drusen can be small, hard and scattered far apart from each other. They are round and have distinct edges. These drusen may not create vision problems for a long time and may not even be an indication of macular degeneration.

Other drusen are larger, softer and closer together. Their edges are less distinct. When these drusen are observed, there is a greater risk for developing wet AMD. They can also disrupt the layers of the retina and can lead to a detachment of the RPE.   

Your doctor can see drusen during a dilated eye exam, even if you are not aware of changes to your vision. That is one reason why regular eye exams are so important. If you have the larger, soft drusen your doctor will probably want you to come for check-ups more often. If they do lead to wet AMD, early treatment is essential.

Wet or exudative AMD, like advanced dry AMD, is also an advanced stage of the disease. Wet AMD, however, has therapeutic options which can preserve and sometimes restore vision.

In wet AMD new blood vessels grow underneath and in the retina. These blood vessels are unhealthy and can leak and bleed causing vision loss. If this happens, then your doctor can offer treatments that try to make the new blood vessels go away.

Patients with wet AMD are monitored closely and may need to visit their doctor and receive treatment every month until the disease is controlled. These treatments are usually injections into the vitreous cavity of the eye or occasionally a laser treatment. Oftentimes with wet AMD, your doctor will perform a fluorescein angiogram of your eyes in the office by injecting a plant-based dye in your vein and taking pictures of your retina over the course of several minutes. This can help your doctor see how the blood vessels are working in your eye. In addition, just like with dry AMD, a retinal scan called Optical Coherence Tomography (OCT) will be performed on your eyes very often, as this allows your doctor to see microscopic changes in your eyes with a non-invasive test.