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Merck Manual

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Interstitial Keratitis

(Parenchymatous Keratitis)


Melvin I. Roat

, MD, FACS, Sidney Kimmel Medical College at Thomas Jefferson University

Last full review/revision May 2020| Content last modified May 2020
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Interstitial keratitis is a serious eye disorder that involves inflammation of the middle layers of the cornea (the clear layer in front of the iris and pupil). It usually occurs in people who have had eye infections.

  • Symptoms include tearing, eye pain, blurred vision, and increased sensitivity to bright light in one or both eyes.

  • Diagnosis is by a doctor's evaluation and blood tests to rule out other diseases.

  • Doctors treat the underlying infection.

An Inside Look at the Eye

An Inside Look at the Eye

Interstitial keratitis is rare in the United States. Most cases occur in children or adolescents as a complication of congenital syphilis. Other causes of interstitial keratitis include Cogan syndrome, Lyme disease, Epstein-Barr virus, acquired syphilis, herpes simplex, varicella-zoster virus, and tuberculosis.


Interstitial keratitis can affect one or both eyes. People develop tearing, eye ache, blurred vision, and increased sensitivity to bright light. Sometimes with interstitial keratitis due to syphilis, the cornea becomes cloudy and can cause permanent vision loss.


  • An eye examination

  • Blood tests

Doctors suspect interstitial keratitis when they see an affected cornea in a person who also has a history of an infection such as syphilis. To examine the cornea, they usually use a slit lamp (an instrument that enables doctors to examine the eye under high magnification).

Blood tests and other tests for syphilis, Lyme disease, and the Epstein-Barr virus are also done. People with interstitial keratitis and normal blood tests should be evaluated for Cogan syndrome.


  • Corticosteroid eye drops

Interstitial keratitis may resolve with treatment of the underlying infection. Sometimes people are treated with a corticosteroid eye drop to decrease inflammation in the cornea.

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