How the Eye Works
The eye is like a camera, creating images by focusing light rays passing through the cornea and the lens to the retina, acting like film, at the back of the eye. When the light converges properly on the retina, the image is in focus and a message is sent to the brain.
The outer covering - the cornea - is more than just a windshield, although it serves that purpose too. The curve of the cornea is a key factor in how well the light is focused on the retina.
If the cornea is too steeply curved, the light focuses in front of the retina, creating myopia, commonly called nearsightedness.
If the cornea is too flat, the light rays converge behind the retina, creating hyperopia, commonly called farsightedness.
If the shape of the cornea is irregular, like the shape of a spoon, then the light rays also are distorted. This is what causes astigmatism.
Lastly, as we age, the lens loses the elastic quality necessary to shift from close to far vision, thus requiring reading glasses for close vision. This is called presbyopia