Clear vision is the result of light entering the cornea (clear window of the eye), passing through the lens inside the eye and coming to a single point of focus on the retina. The most common types of visual distortions are nearsightedness, farsightedness and astigmatism.
How the Normal Eye WorksThe human eye functions much like a camera, with a lens in front and a light-sensitive screen, the retina, in the rear.
Images enter the eye through the cornea, a transparent domed window at the front of the eye. In normal eye, the cornea bends (refracts) incoming images, causing the images to focus on the retina.