The resources of the REP were used to identify all Olmsted County residents who sought care for potential acute HZO between January 1, 1976, and December 31, 1998. Medical records were retrieved for all patients with diagnostic codes related to HZO and its complications. Assigned diagnostic codes were based on Mayo Clinic modifications of the International Classification of Diseases, Ninth Revision, Clinical Modification36 and included codes 530110 (herpes zoster, eye), 530111(herpes zoster ophthalmicus), 530112 (keratitis, herpetic [zoster]), 530120(dermatitis, eyelid, herpes zoster), 530130 (keratoconjunctivitis, due to herpes zoster), 530140 (iridocyclitis, due to herpes zoster), 530150 (keratouveitis[herpes zoster]), 539120 (keratitis, postherpetic). We also screened charts with the following diagnoses to determine if patients did, in fact, have HZO: 531111 (herpes zoster, face, except eye), 531112 (herpes zoster, cranial nerves), 531113 (herpes zoster, trigeminal), 531121 (herpes, geniculate ganglionitis), 538110 (herpes zoster, nose), 538111 (shingles), 539110 (herpes zoster, late effect of), 539111 (neuralgia, herpetic), 539112 (neuritis, herpetic), and all cases of herpes zoster in which the affected dermatome was not specified. Cases coded as having nonophthalmic trigeminal zoster (ie, Ramsay Hunt syndrome), varicella zoster, and herpes simplex virus were not retrieved. Trained nurse abstractors or one of the coauthors reviewed all medical records to identify all true cases of acute HZO during the study period. The complete medical records for all confirmed cases were then abstracted by a medical student investigator (E.A.S.) to include information on demographics, antiviral and ocular therapy, ocular complications and outcomes of the disease, number of medical visits, and dates of symptom onset, diagnosis, initiation of therapy, and complications. The senior clinician-investigator (K.H.B.) also reviewed all ophthalmologic records for every patient identified as having any complication or adverse outcome other than conjunctivitis. Because specific complications of HZO were treated as statistical end points, we defined each complication and adverse outcome prior to reviewing the records (Table 1). If such an end point occurred and was judged by the senior clinician-investigator to be clearly unrelated to HZO (eg, bilateral open-angle glaucoma 10 years after the onset of HZO), then this end point was excluded from the analysis of HZO-related complications or outcomes.