Merck Manual

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Interstitial Keratitis

(Parenchymatous Keratitis)

By

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 Syphilis in Newborns Syphilis is an infection caused by the bacteria Treponema pallidum. It causes serious problems in infants infected before birth. Syphilis is caused by bacteria. Serious complications may develop... read more Syphilis in Newborns . Other causes of interstitial keratitis include Cogan syndrome Cogan Syndrome Cogan syndrome is a rare autoimmune disease of the eye that can affect the cornea. Eye pain, decreased vision, increased sensitivity to bright light, and redness of the eye are common symptoms... read more , Lyme disease Lyme Disease Lyme disease is a tick-transmitted infection caused by Borrelia species, primarily by Borrelia burgdorferi and sometimes by Borrelia mayonii in the United States. These spiral-shaped bacteria... read more Lyme Disease , Epstein-Barr virus Infectious Mononucleosis Epstein-Barr virus causes a number of diseases, including infectious mononucleosis. The virus is spread through kissing. Symptoms vary, but the most common are extreme fatigue, fever, sore throat... read more Infectious Mononucleosis , acquired syphilis Syphilis Syphilis is a sexually transmitted disease caused by the bacteria Treponema pallidum. Syphilis can occur in three stages of symptoms, separated by periods of apparent good health. It begins... read more Syphilis , herpes simplex Herpes Simplex Virus (HSV) Infections Herpes simplex virus infection causes recurring episodes of small, painful, fluid-filled blisters on the skin, mouth, lips (cold sores), eyes, or genitals. This very contagious viral infection... read more Herpes Simplex Virus (HSV) Infections , varicella-zoster virus Shingles Shingles is a painful skin rash caused by a viral infection that results from reactivation of the varicella-zoster virus, the virus that causes chickenpox. What causes the virus to reactive... read more Shingles , and tuberculosis Tuberculosis (TB) Tuberculosis is a chronic contagious infection caused by the airborne bacteria Mycobacterium tuberculosis. It usually affects the lungs. Tuberculosis is spread mainly when people breathe air... read more Tuberculosis (TB) .

Symptoms of Interstitial Keratitis

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.

Diagnosis of Interstitial Keratitis

  • 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 Slit-Lamp Examination A person who has eye symptoms should be checked by a doctor. However, some eye disorders cause few or no symptoms in their early stages, so the eyes should be checked regularly (every 1 to 2... read more (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 Cogan Syndrome Cogan syndrome is a rare autoimmune disease of the eye that can affect the cornea. Eye pain, decreased vision, increased sensitivity to bright light, and redness of the eye are common symptoms... read more .

Treatment of Interstitial Keratitis

  • 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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Test your knowledge

Eye Redness
Eye redness is a condition in which the part of the eye that is normally white appears reddish. This occurs when blood vessels on the surface of the eye widen (dilate), bringing extra blood to the eye. Which of the following is NOT a frequent cause of eye redness? 
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