Infectious processes in the uveal tract may be restricted to that layer of the eye or may be part of a generalized inflammatory process affecting multiple or all coats of the eye. If the eye is the primary source of the infection (eg, as in posttraumatic bacterial infection), that infection is termed exogenous. If, however, the infection originates elsewhere in the body (eg, a ruptured diverticulum) and subsequently spreads hematogenously to involve the uveal tract, the infection is referred to as endogenous. A wide variety of organisms can cause infections of the uveal tract, including bacteria, fungi, viruses, and protozoa.
Histologic examination often shows a mix of acute and chronic inflammatory cells within the choroid, ciliary body, or iris stroma. In cases of infection with viral, fungal, or protozoal (eg, toxoplasmosis) agents, epithelioid histiocytes are typically present (granulomatous inflammation). If infection is suspected, special stains for microorganisms may be helpful (Fig 12-7).
Figure 12-7 Infectious uveitis, with the infectious organisms demonstrated with special stains. A, Gram-positive bacilli seen on Gram stain. B, Filamentous fungi seen with Gomori methenamine silver (GMS) stain. C, Filamentous fungi on periodic acid–Schiff (PAS) stain.
(Courtesy of Steffen Heegaard, MD.)
See Chapter 2, Table 2-2, which presents histochemical stains commonly used in ophthalmic pathology.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.