What Is Macular Degeneration? - Symptoms, Causes & Treatment

Instructor: Catherine Konopka

Catherine has taught various college biology courses for 5 years at both 2-year and 4-year institutions. She has a Ph.D. in cell and molecular biology.

Imagine that you were slowly losing your sense of sight, and there was not much that you could do about it! In this lesson, you will learn about one of the leading causes of age-related vision loss: macular degeneration.

Age-Related Macular Degeneration

If you know someone who is slowly losing his or her vision, it is possible that he or she has age-related macular degeneration or AMD. AMD is a form of progressive vision loss, which means it gets worse as you age. At age fifty, you will have a 1.5% chance of developing AMD. If you live to be eighty, there is a 15% chance you will develop AMD. Before we get into the causes and symptoms of AMD, let's first briefly review the anatomy of the eye.

Seeing With Your Retina

When you look at something, light rays enter your eye and pass through the cornea and lens, which bend the light rays so they form an in-focus image on the retina at the interior back of the eye ball. The retina is made up of millions of small nerve cells, some of which are photoreceptors. The photoreceptors detect the light rays and convert the light signal into an electrical signal that travels to the brain. The retina lies just interior to a layer of blood vessels called the choroid.

If we compare your eye to a camera, the retina is like the film or digital detector. If any part of the digital detector is damaged, that pixel of your photograph will be black. Likewise, if any part of your retina is damaged, you will not be able to see anything in that part of your visual field. It's like having 'dead pixels' on your computer monitor. The choroid, on the other hand, is like the battery that brings energy to the parts of the camera. If the battery in a camera leaks, the detector is ruined. Similarly, if blood vessels in the choroid leak, the retina will be damaged.

Important features of the eye for AMD.
The anatomy of the eye

The Macula: The Most Sensitive Part of the Retina

Your retina stretches the entire back interior of your eye ball. Objects in your peripheral vision are detected at the lateral edges of the retina. Objects right in front of you are detected directly behind your lens in an area of the retina called the macula. Take a second to pay attention to an object directly in front of you. Now pay attention to the objects in your peripheral vision. Which ones are sharper or clearer? If you are in a lighted room, it is probably the objects directly in front of you. That's because photoreceptors are the most concentrated directly behind your lens. The macula is the area of the retina that has the highest concentration of photoreceptors and is responsible for detecting objects directly in front of you.

Two Types of AMD

In AMD, nerve cells of the macula die over time. If the photoreceptors that convert the light into an electrical signal die, then your brain will never know that you are looking at something and there will be dark spots in your field of vision. There are two types of AMD.

  • In geographic atrophy AMD (aka dry AMD), the most common form of AMD, cells called retinal pigment cells (RPCs) die. RPCs are like the caretakers of the photoreceptors. They provide nutrients to the photoreceptors. Without the RPCs, the photoreceptors will eventually die as well. We don't know exactly why the RPCs die, but it may be due to fatty deposits called drusen, which are the hallmark of dry AMD. In general, the more drusen that are present, the more advanced the AMD. Researchers aren't exactly sure where the drusen come from. One possibility is that they are left over material from aging cells.
  • In neovascular AMD (aka wet AMD), which causes more severe vision loss, new blood vessels grow uncontrollably just between the retina and choroid. These blood vessels can leak fluid that damages the photoreceptors in the macula. It's like a battery that corrodes and ruins the electronics of your camera. Wet AMD develops once someone has dry AMD, even if there are no symptoms or vision loss from dry AMD.

Symptoms of AMD

The most common symptom of AMD is the presence of drusen that can be detected during an eye exam. The appearance of drusen may not be accompanied by any other symptoms, especially in early stages. However, as AMD progresses, the following symptoms may appear:

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