How we see depends upon the transfer of light. Light passes through the front of the eye (cornea) to the lens. The cornea and the lens help to focus the light rays onto the back of the eye (retina). The cells in the retina absorb and convert the light to electrochemical impulses which are transferred along the optic nerve and then to the brain.
The lens of the eye helps us to focus but sometimes needs some additional help in order to focus clearly. Glasses, contact lenses, and artificial lenses all help us to see more clearly.