When we talk about vision, we think about two parts of the vision, the central portion of the vision and the peripheral part of the vision. The central vision is going to have to do more with a macula, which is where most of the cones are densely located. These cones are going to be more responsible for your really sharp detailed vision as well as your color vision. If a patient has a medical condition, such as macular degeneration or diabetic retinopathy amongst other diseases, then we could have a reduction in the central visual acuity. Basically, we have physical damage that occurs to the central part of the retina. And that decreases the vision.

Typically, when somebody comes to the eye doctor, the eye doctor is looking to be able to correct them to 20/20 vision. When a person has an eye disease, and it damages the retina, they will no longer be correctable to 20/20. Once a person is no longer able to be corrected to 20/20 vision,  which in a lot of cases is once we get to about 20/70 visual acuity, they are then classified as being in the low vision category. When a patient gets to 20/200, that's considered legally blind. In these cases, when somebody starts to have difficulty with central vision, then we can teach them to do what's called eccentric viewing. And in that case, they learn to use the adjacent unaffected peripheral retina to view with instead of the central retina. Of course, it's not going to be as good visual acuity as someone with 20/20 vision, but they're still going to be able to utilize that retina so they don't go completely blind.