subject: The Cornea [print this page] Covering the iris, pupil and anterior chamber in the front of the eye, is a transparent part called the cornea. Refracting light is the main function of the cornea and it accounts for two-thirds of the eye's total optical power. Vision disorders, called refractive errors, are the most common of all vision problems in the nation. According to the National Eye Institute, about 120 million people in the United States wear eyeglasses or contact lenses to correct refractive errors.
Types of Refractive Errors
Refractive errors are the most common type of vision problems in our country. If you have a refractive error, you probably have seen an eye doctor in your area to correct your vision. Refractive errors fall into three types that are:
Myopia (nearsightedness) when the cornea is curved too much, or the eye is too long, objects at a distance are blurry because they are focused in front of the retina
Hyperopia (farsightedness) opposite of myopia, farsightedness always clear distance vision while close vision is blurry and this happens because images focus on a point beyond the retina
Astigmatism the uneven curve of the cornea blurs and distorts both distance and close-up vision because the curvature causes light rays to have multiple focal points and focus occurs in two separate areas of the retina
Twenty-five percent of all Americans are myopic, and two-thirds of those with myopia have astigmatism.
Cornea and Medical Terminology
Medical terms related to the cornea often begin with the prefix "kerat-", derived from the Greek language. Some words that your eye doctor may use that relates to the cornea include:
Photoreactive Keratotomy (PRK) a surgical alternative to LASIK
Keratonus Eye Disease a progressive disease where the cornea thins and starts to bulge into a cone-like shape
Function of the Cornea
Due to the cornea's durability and smooth shape, it helps the eye in several ways. The cornea protects the rest of the eye from debris, like dust, germs and other particulates. It shares this shielding function with the eyelid, eye socket, tears and sclera (white part of the eye). The cornea also performs as the eye's outermost lens. Much like a window, the cornea controls and focuses the onslaught of light coming into the eye. Likewise, the cornea also acts as a light filter, to screen out the most harmful ultraviolet (UV) rays.
The Cornea's Response to Injury
Minor injuries and abrasions have little effect on the cornea's tough surface. Healthy cells quickly slide over and patch the injury before infection sets in and vision is negatively affected. However, if the scratch is deeper, the injury could take much longer to heal. With these deeper abrasions, vision is impacted and the symptoms include:
