Interstitial keratitis, a manifestation of certain corneal infections, is rare in the US. Most cases occur in children or adolescents as a late complication of congenital syphilis Congenital Syphilis Congenital syphilis is a multisystem infection caused by Treponema pallidum and transmitted to the fetus via the placenta. Early signs are characteristic skin lesions, lymphadenopathy, hepatosplenomegaly... read more 
. Ultimately, both eyes may be involved. A similar but less dramatic bilateral keratitis occurs in Cogan syndrome Cogan Syndrome Cogan syndrome is a rare autoimmune disease involving the eye and the inner ear. Cogan syndrome affects young adults, with 80% of patients between 14 and 47 years. The disease appears to result... read more , Lyme disease Lyme Disease Lyme disease is a tick-transmitted infection caused by the spirochete Borrelia species. Early symptoms include an erythema migrans rash, which may be followed weeks to months later by neurologic... read more 
, and Epstein-Barr virus infection Infectious Mononucleosis Infectious mononucleosis is caused by Epstein-Barr virus (EBV, human herpesvirus type 4) and is characterized by fatigue, fever, pharyngitis, and lymphadenopathy. Fatigue may persist weeks or... read more 
. Rarely, acquired syphilis Syphilis Syphilis is caused by the spirochete Treponema pallidum and is characterized by 3 sequential clinical, symptomatic stages separated by periods of asymptomatic latent infection. Common manifestations... read more 
, herpes simplex Herpes Simplex Virus (HSV) Infections Herpes simplex viruses (human herpesviruses types 1 and 2) commonly cause recurrent infection affecting the skin, mouth, lips, eyes, and genitals. Common severe infections include encephalitis... read more 
, herpes zoster Herpes Zoster Herpes zoster is infection that results when varicella-zoster virus reactivates from its latent state in a posterior dorsal root ganglion. Symptoms usually begin with pain along the affected... read more 
, or tuberculosis Tuberculosis (TB) Tuberculosis (TB) is a chronic, progressive mycobacterial infection, often with a period of latency following initial infection. TB most commonly affects the lungs. Symptoms include productive... read more 
may cause a unilateral form in adults.
(See also Introduction to Corneal Disorders Introduction to Corneal Disorders Symptoms that suggest corneal involvement (eg, rather than simple conjunctivitis) include unilateral involvement, pain (foreign body sensation and ache—not just a gritty sensation), particularly... read more .)
Symptoms and Signs of Interstitial Keratitis
Photophobia, pain, lacrimation, and vision blurring are common. The lesion begins as patches of inflammation in the mid-stroma that cause opacification. Typically with syphilis and occasionally with other causes, the entire cornea develops a ground-glass appearance, obscuring the iris. New blood vessels grow in from the limbus (neovascularization) and cause orange-red areas (salmon patches). Anterior uveitis and choroiditis are common in syphilitic interstitial keratitis. Inflammation and neovascularization usually begin to subside after 1 to 2 months. Some corneal opacity usually remains, causing mild to moderate vision impairment.
Diagnosis of Interstitial Keratitis
The specific etiology must be determined. The stigmas of congenital syphilis, vestibuloauditory symptoms, history of an expanding rash, and tick exposure support specific etiologies. However, all patients should have serologic testing, including all of the following:
New tests such as Treponema pallidum particle agglutination assay, Treponema pallidum enzyme immunoassay, chemiluminescence immunoassay, and nucleic acid amplification tests (NAAT) may also be useful in diagnosing ocular syphilis.
Patients with negative serologic test results may have Cogan syndrome Cogan Syndrome Cogan syndrome is a rare autoimmune disease involving the eye and the inner ear. Cogan syndrome affects young adults, with 80% of patients between 14 and 47 years. The disease appears to result... read more , an idiopathic syndrome consisting of interstitial keratitis and vestibular and auditory deficits. To prevent permanent vestibuloauditory damage, symptoms of hearing loss, tinnitus, or vertigo require urgent referral to an otolaryngologist.
Treatment of Interstitial Keratitis
Key Points
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Interstitial keratitis, which is rare in the US, involves chronic inflammation of the middle corneal layers.
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Findings include pain, tearing, decreased visual acuity, and often orange-red discoloration of the cornea and anterior uveitis.
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Test patients for syphilis, Lyme disease, and Epstein-Barr virus infection.
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Treatment is by an ophthalmologist; sometimes topical corticosteroids are prescribed.
