How the Eye works

In order to see clearly, objects need to be brought to a focus point
precisely on the retina of the eye. The retina can be compared to the
film in a camera. The light is brought to a focus point by the cornea
and lens of the eye. The cornea's curvature is ideally matched to it's
length in the normal eye. As the normal eye ages, the lens loses the
ability to focus for reading and will require the help of reading
glasses. This usually begins to affect most people after the age of 40.





If you are nearsighted, the cornea of your eye is overly curved or your
eyeball is too long. This combination brings images of distant objects
(street signs) to a focus point in front of the retina. When the light
reaches the retina, a blurred image is seen since the light rays spread
apart after the focus point.






If you are farsighted, the cornea of your eye is not curved enough or
your eyeball is too short. This combination of factors causes the focus
point of the eye to be located behind the retina. When light reaches the
retina, a blurred image is seen since the light rays have not been
brought to focus prior to reaching the retina.






If you have astigmatism, the cornea of your eye has a non-spherical
shape (like a football) and does not bring light to focus at a single
point. Instead, it focuses images over a range of points producing a
blurred image. Both nearsighted and farsighted eyes can also have
astigmatism.