The normal eye

This drawing is an inside view of the
eye of a person with normal vision.

Myopia or "nearsightedness"

Myopia is a hereditary condition in which the eye is either longer than it should be, or the cornea has too much curvature. People with myopia can usually read without glasses, but they cannot see far away without glasses or contact lenses.

Here is the flower seen by a person
with myopia...

Astigmatism - uneven cornea

Light entering the eye is distorted by
the lack of sphericity, causing blurry
images and ghost images. Astigmatism
is often combined with myopia or
hyperopia.

The flower, as seen by a person with astigmatism. People with astigmatism
see ghost images or double images
without their glasses on. In this condition,
the cornea is not spherical, but is shaped more like a football or teaspoon.

Presbyopia

Presbyopia is age-related loss of reading vision. As people age, they begin to lose the ability to focus on things up close, unless they have their reading glasses or bi-focals on. This problem can be treated surgically with LASIK by creating monovision, with one eye corrected for distance and the other eye corrected for reading. Surprisingly, patients adapt to this very well in most cases. Another way to correct this problem is with multifocal intraocular lenses, which have been implanted for the past few years. These lens implants replace the natural lens in cataract surgery, allowing the patient to see both far away and up close with both eyes. Both of these techniques allow most patients to go without glasses most of the time, although some fine-tuning with glasses may be necessary in some cases.

Hyperopia or "Farsightedness"

"Farsightedness" occurs when the eye is either too short or the cornea doesn't have enough curvature and light comes into focus behind the retina. Young people with farsightedness can usually see pretty well, but as they get older, they lose their ability to focus up close and also
far away.