What is keratitis?

Quick Answer
An inflammation of the cornea caused most often by the herpes simplex virus.
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Causes and Symptoms

Keratitis produces an inflammation or irritation of the cornea, the outer transparent layer of the eye. It is generally caused when the cornea has been scratched, cut, or injured so that a pathway is established for the entry of infectious agents. The resulting infection may be superficial or may involve deeper layers of the cornea. The most common cause of keratitis is the herpes simplex virus, the same virus that produces cold sores. Initially, the virus causes inflammation of the conjunctiva, the membrane lining the eyelid. Typically, it then produces infection of the cornea with branchlike ulcerations. Less common causes of keratitis include adenoviruses, varicella zoster virus, bacteria, fungi, parasites, excessive exposure to ultraviolet light, vitamin A deficiency, rheumatic diseases, surgery on the cornea, adverse reaction to broad-spectrum antibiotics, trauma to the eye that leaves scar tissue, allergic reactions to eye makeup or other irritants, and congenital syphilis (often termed interstitial keratitis). Bacterial keratitis usually results from improper cleaning or care of contact lenses.

The symptoms of keratitis typically include one or more of the following: eye redness, tearing and itching of the eye, a sensation that foreign matter is in the eye, blurred vision or reduction of vision clarity, eyelids sticking together, pain, eye discharge, sensitivity to light, and cloudy appearance of the cornea. If keratitis is left untreated, then corneal tissue can be destroyed, scar tissue can form, and feeling in the cornea may eventually be lost. At the first sign of eye infection, proper treatment should be administered.

Treatment and Therapy

Medical treatment of keratitis varies according to the cause. Antiviral eyedrops are administered for viral keratitis. Oral or eyedrop antibiotics are used for other infections. Some ophthalmologists prefer to scrape diseased tissue from the cornea, apply anesthetic eyedrops, and cover the eye temporarily with a patch. Later, the patient may wear a special type of contact lens to prevent a reoccurrence of the infection. For cases involving dry eyes, artificial tears are prescribed for lubrication. Contact lenses may need to be replaced. In the case of vitamin A deficiency, supplements and foods rich in vitamin A (such as carrots, mangoes, spinach, squash, and liver) are prescribed.

Perspective and Prospects

Approximately fifty thousand cases of keratitis are diagnosed worldwide each year. It is the most common cause of corneal blindness in the United States. If treatment for keratitis is started early, then it is typically very effective. In the treatment of keratitis caused by the herpes simplex virus, it is very important not to use topical corticosteroids, as they may worsen the infection and even lead to blindness. Because herpes simplex virus remains in the body after treatment, there is a 50 percent chance that keratitis may reoccur.


Parker, James N. and Philip M. Parker. Keratitis: A Bibliography, Medical Dictionary, and Annotated Research Guide to Internet References. San Diego, Calif.: Icon Health, 2004.

Parker, James N., and Philip M. Parker, eds. The Official Patient’s Sourcebook on Keratitis. San Diego, Calif.: Icon Health, 2002.

Vorvick, Linda J. "Corneal Ulcers and Infections." MedlinePlus, March 22, 2013.

Wilhelmus, Kirk R., and Thomas J. Liesegang, eds. Interstitial Keratitis. Philadelphia: W. B. Saunders, 1994.