The ocular complications of smallpox and smallpox immunization

Although smallpox was eradicated worldwide, concerns have been raised about the use of smallpox as a biological weapon. Plans are being considered for smallpox immunization in the United States. Variola virus, the cause of smallpox, and vaccinia virus, used in smallpox immunization, are both orthopoxviruses that are associated with serious ocular complications, including eyelid and conjunctival infection, corneal ulceration, disciform keratitis, iritis, optic neuritis, and blindness. About 5% to 9% of patients with smallpox develop ocular complications, and case-fatality rates reach 20% to 35% among unvaccinated individuals. About 10 to 20 patients develop ocular complications per 1 million smallpox immunizations, usually through autoinoculation, in which the patient transfers vaccinia from the immunization site to the eye. The risk of ocular vaccinia infection may be reduced by instructing patients and individuals in close contact with the vaccinee to wash their hands often and avoid touching the immunization site and their eyes. Topical antiviral therapy, topical steroids, and topical and oral antibiotics have been used to reduce the ocular complications of smallpox immunization. In contrast, there has been little experience with the use of these therapies for the ocular complications of smallpox.