How Contact Lenses Correct Vision
Contact lenses are designed to rest on the cornea, the clear outer surface of the eye. They are held in place mainly by adhering to the tear film that covers the front of the eye and, to a lesser extent, by pressure from the eyelids.
As the eyelid blinks, it glides over the surface of the contact lens and causes it to move slightly. This movement allows the tears to provide necessary lubrication to the cornea and helps flush away debris between the cornea and the contact lens.
Contact lenses are optical medical devices, primarily used to correct nearsightedness, farsightedness, astigmatism and presbyopia. In these conditions, light is not focused properly on the retina, the layer of nerve endings in the back of the eye that converts light to electrochemical impulses. When light is not focused properly on the retina, the result is blurred or imperfect vision.
When in place on the cornea, the contact lens functions as the initial optical element of the eye. The optics of the contact lens combine with the optics of the eye to properly focus light on the retina. The result is clear vision.