Can sense organs like the eye really evolve?

Eyesight is a good example of the power of natural selection. Prior to the development of vision correcting technology, those with poor eyesight were subject to selection pressures for good vision, such as are associated with hunting or detecting threats. With the invention of eyeglasses these types of selection pressures were removed, and genes for poor vision were passed on indiscriminately. As time went by the average quality of human vision has diminished. Indeed, Darwin noted on his voyage through Patagonia that the natives appeared to have significantly better visual acuity than the Europeans from the ship.