Vision Terminology

Nearsightedness

Also known as myopia, the light entering the eye doesn't focus on the retina, but at some point in front of it. It is frequently caused by an abnormally long eye shape, or by an excessive curvature of the cornea. When this occurs, objects at a distance appear blurry.  Most nearsighted patients get their first pair of glasses in elementary school, and wear them for the rest of their lives, although they can usually remove their glasses to see objects up close without correction.

Farsightedness

Also known as hyperopia, the light entering the eye focuses at a point behind the retina, making objects closer to the eyes blurry, while those far away are in focus. It is frequently caused by an abnormally short shaped eye, or an excessively flat cornea.  Most farsighted patients wear glasses when they are very young and the find that they don't need them while in their 20s and 30s.  Once they are in their 40s they start to need them again, at first for near and then for all tasks. 

Astigmatism

This is caused not by the length of the eye, but the shape. The normal cornea is shaped like a ball. An astigmatic eye, however, takes a football-like shape. The result is that objects are not focused into a single image. Vision is blurred and distorted at both near and distance without their glasses. 

Presbyopia

The inability to focus on objects close-up. The condition occurs when the lens of the eye loses its ability to focus at close range. It is a normal occurrence, usually beginning in the early forties, tending to decrease visual acuity with age.