The lens of the eye is a notable exception when it comes to damaged cells being repaired or replaced. The cells of the lens of the eye are never replaced; the proteins of the lens are never replenished. The lens cannot repair itself; damage accumulates over a lifetime.
Unlike cataracts, little can be done to treat retinal diseases. Unlike the lens, the retina is irreplaceable. Macular degeneration, the accumulation of damage in the retina, is the leading cause of blindness from retinal disease. Slowly over the years the macula is irreversibly damaged by exposure to UV radiation.
About one third of adults over age 65 experience this steady decline of central vision, not correctable by glasses.