Macular degeneration is a disease that affects the center of the visual field. Central vision is needed for activities like reading, driving, and recognizing people. When looking directly at a person, central vision allows you to be able to see a person’s face and recognize them. In the same way, when watching television, you use your central vision to be able to enjoy the show.
A choroidal nevus is a common, benign, pigmented growth similar to a mole on your skin, which happens to be located beneath the retina. As your skin has pigmented cells (called melanocytes), so does the layer underneath the retina, called the choroid.
Moreover, as your skin can have a mole or freckle which is a collection of those melanocytes, you can also have a collection of these cells inside or on your eye. This is called a nevus (nevi for plural).
These nevi are common. It is estimated that somewhere between 6-7% of the Caucasian population will have a choroidal nevus, and Caucasian people are more likely to develop nevi than other races. Most nevi are either present at birth, or develop by 20 years of age.