Infectious Scleritis

Although systemic immune-mediated diseases are the main possibilities in the differential diagnosis of scleritis, other unusual etiologies, such as infectious diseases, must also be considered. Infectious scleritis, either endogenous or exogenous, may be caused either by a direct invasion of organisms that cause the systemic and local signs, or by an immune response induced by the infectious agent.

All classes of microbial organisms can infect the sclera, including bacteria, fungi, viruses, and parasites (Table 7.1). As the scleritis caused by these conditions may be identical to that caused by immune-mediated diseases, the challenge for the ophthalmologist is to distinguish infectious scleritis from other inßammatory conditions of the sclera. The differential diagnosis between both groups of diseases is important because infectious etiologies are usually treatable with speciÞc therapy, and because corticosteroid therapy or immunosuppressive therapy, often used in scleritis associated with immune-mediated diseases, is contraindicated in active infection; if topical or systemic corticosteroids are started because it is thought the scleritis has an immunologic basis, scleral destruction, and extension of the microbial process may progress.

In evaluating a patient with scleritis, it is important to take a history not only for evidence of underlying systemic diseases, but also for trauma, contact lens effects, past ocular conditions, topical therapy, and surgical procedures.

There are no speciÞc clinical signs that conÞrm scleral infection. When the diagnosis is suspected, laboratory studies are required to establish the causative agent. Appropriate therapy is initiated on the basis of clinical suspicion, the results of initial laboratory studies, and knowledge of the most likely responsible organisms responsible. The plan may be modiÞed later, depending on the clinical response and laboratory results. With advanced infection or with a severe host inßammatory response, devastating complications can occur, resulting in structural alterations, such as thinning, perforation, or extension to adjacent structures.

In theory, any infectious agent that induces an immune response can cause vasculitis. Bacteria, such as Pseudomonas, Streptococcus, Staphylococcus, or viruses such as herpes simplex virus (HSV) or Varicella-zoster virus (VZV) may be associated with small-sized vessel vasculitis. Syphilis and tuberculosis may cause large-sized vessel vasculitis (aortitis). Vascular damage is commonly incurred by direct invasion or the vessel by the organism, or by embolization, both of which result in an inßammatory response and immune complex formation and deposition.

This chapter focuses on the infectious diseases that may be associated with scleritis. Recommendations for an approach to the management and therapy of infectious scleritis are presented.