2020–2021 BCSC Basic and Clinical Science Course™
8 External Disease and Cornea
Chapter 10: Infectious Diseases of the External Eye: Microbial and Parasitic Infections
Microbial and Parasitic Infections of the Cornea and Sclera
Bacterial and fungal infections of the sclera are very rare. Most cases result from the extension of microbial keratitis involving the peripheral cornea. Trauma and contaminated foreign bodies (including scleral buckles) are possible risk factors. Bacterial scleritis has also occurred in sclera damaged by previous pterygium surgery, especially when beta irradiation or mitomycin has been used (Fig 10-25). Bacteria and fungi can also invade tissue of the eye wall surrounding a scleral surgical wound, but endophthalmitis is more likely in this setting. Scleral inflammation can also be a feature of syphilis, tuberculosis, or leprosy, or infection with Acanthamoeba species, Nocardia species, or atypical mycobacteria. Tuberculous scleritis should be considered in chronic steroid-dependent scleritis or in the setting of surgically induced necrotizing scleritis (SINS). Diffuse or nodular scleritis is an occasional complication of varicella-zoster virus eye disease.
Figure 10-24 Subconjunctival loiasis.
(Courtesy of Woodford S. Van Meter.)
Figure 10-25 Bacterial scleritis occurring 2 weeks after pterygium surgery.
(Courtesy of Kirk R. Wilhelmus, MD.)
Evaluating suppurative scleritis is similar to evaluating microbial keratitis. Smears and cultures are obtained before antimicrobial therapy is begun. If the overlying epithelium is intact, a scleral or episcleral biopsy should be performed to obtain specimens for culture, histologic examination, and molecular diagnostic testing. The workup of nonsuppurative scleritis is guided by the history and findings from the physical examination, as described in Chapter 11.
Topical antimicrobial therapy is begun just as for microbial keratitis. Because of the difficulty in controlling microbial scleritis, subconjunctival injections and intravenous antibiotics may also be used. Long-term oral therapy shows promise.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.