At the front of the eye you have the eyeball surface, made up of several layers, and the lens, that lets you focus images on the back of the eye. With age (usually from your 40s) your lens becomes less efficient at focusing, accounting for the inevitable middle-age glasses. On the inner surface of the eyeball is the retina, packed with light-detecting cells.
This is a companion discussion topic for the original article at https://patient.info/news-and-features/eye-problems-age-cataracts-macular-degeneration-glaucoma-prevention