The cornea is the clear "window" at the front of the eye that sits like a watchglass over the colored iris.  The cornea is the main part of the eye's focusing system, so any irregularities or distortion of the corneal surface will profoundly affect vision.

Keratoconus is a condition in which the cornea weakens and becomes cone-shaped, like a weak spot in a tire.  This distorts its focusing ability and results in blurred vision. It usually begin in the middle to late teenage years.  The degenerative process continues until sometime between the ages of 25 to 40, when it slows down or stops.  Keratoconus usually affects both eyes, though its severity may be different in each eye.  It occurs in both sexed and all races.  It is an inherited condition that sometimes occurs as part of other hereditary conditions.

The first symptom of keratoconus may be sudden large increase in nearsightedness that is not very much different from typical progression of nearsightedness.  For a while, vision may still be corrected to 20/20 with glasses, but eventually vision deteriorates and can no longer be corrected to 20/20/  Images become severely blurred or distorted.  Glare problems, especially noticeable when driving at night, and "rainbows" and "rings" around lights can also occur.  Very rarely, vision in an eye can blur suddenly or even be lost- and then recovered partially on its own.  This is called hydrops (water-swelling) of the cornea.

The diagnosis of keratoconus, even at its early stage, can readily be made from "corneal topography".  This is done routinely before laser surgery for nearsightedness to rule this condition as patients with keratoconus are not good candidate for laser surgery.

As long as visual problems are slight, they can be managed by changing the prescription of your glasses.  When an eye can not be adequately corrected with glassed, a contact lens often provides good vision. If the keratoconus continues to progress, the time may come when you can no longer wear contact lenses, either for reasons of comfort or because the cornea has become so distorted that the lens will not stay in place.  At that time, a corneal transplant may be necessary.  In this surgical procedure, a normal donor cornea is used to replace the abnormal cone-shaped cornea.  Corneal transplants for keratoconus are highly successful.  Even after a successful transplant, however, you may still need to wear eyeglasses or contact lenses to obtain good vision.  Since the corneal problem usually stabilizes by the age of 40, you are not likely to require surgery after that age if you did not need it before then.