Etiology of immune stromal (interstitial) keratitis

We compared the etiologies of immune stromal keratitis (ISK), also known as interstitial keratitis (IK), in a recent group of patients with active and inactive ISK.

We reviewed the charts of 97 patients seen in the cornea clinic at the University of Minnesota from 1985 through 1994. Fifty-five patients were classified as having active ISK, defined by stromal inflammation without ulceration within 1 year of presentation. Forty-two patients were identified as having inactive ISK, defined by evidence of past stromal inflammation including stromal scarring, stromal thinning, ghost vessels, and reduplication of Descemet's membrane without active inflammation for the 1 year before presentation. We determined the etiology of the ISK by careful review of the patient's ocular examination, as well as medical and laboratory workup. Patients were labeled with the diagnosis of idiopathic ISK if no identifiable etiology was found.

Herpes simplex virus (HSV) accounted for 71.4% of unilateral active ISK. Idiopathic accounted for 14.3%, and varicella-zoster virus accounted for 8.6% in this group. HSV was the etiologic factor of 50.0% of inactive unilateral cases, whereas 33.3% were idiopathic. Sixty percent of cases of bilateral, active ISK were from idiopathic causes. Syphilis was the cause of 48.5% of bilateral inactive cases. In this group, 33.3% were from idiopathic causes.

Although syphilis has been recognized for many years as the cause of 90% of cases of ISK, this is no longer true. We demonstrated that active ISK is most commonly caused by HSV or is idiopathic and that, although syphilis is the leading cause of inactive, bilateral ISK, it is responsible for only 18.6% of total cases.