The cornea is a thin, clear, spherical layer of tissue on the surface of the eye that provides a window for light to pass through. In a healthy eye, the cornea bends or refracts light rays so they focus precisely on the retina in the back of the eye.
Diabetic retinopathy is a complication of diabetes that weakens the blood vessels that supply nourishment to the retina (the light-sensitive lining in the back of the eye where vision is focused).
The macula is a part of the retina in the back of the eye that ensures that our central vision is clear and sharp. Age-related macular degeneration (AMD) is a disease that degrades the central vision.