choroid, or all 3 structures. Histologically, colobomas appear as an area nearly or entirely devoid of tissue. See BCSC Section 2, Fundamentals and Principles of Ophthalmology, and Section 6, Pediatric Ophthalmology and Strabismus, for further discussion of uveal colobomas.
Inflammations
BCSC Section 9, Intraocular Inflammation and Uveitis, discusses the conditions described in the following sections and also explains in depth the immunologic processes involved.
Infectious
The uveal tract may be involved in infectious processes that appear restricted to a single intraocular structure or that may be part of a generalized inflammation affecting several or all coats of the eye. If the eye is the primary source of the infection, as with posttraumatic bacterial infection, the infection is termed exogenous. If, however, the infection originates elsewhere in the body, such as with 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.
Histopathology often shows a mixed acute and chronic inflammatory infiltrate within the choroid, ciliary body, or iris stroma. In cases of viral, fungal, or protozoal (eg, toxoplasmosis) agents, the presence of epithelioid histiocytes is typical (granulomatous inflammation). Special stains (see Table 3-2) for microorganisms (tissue Gram, Gomori methenamine silver, PAS [periodic acid–Schiff], Ziehl-Neelsen) may be helpful if infection is suspected.
Noninfectious
Sympathetic ophthalmia
Sympathetic ophthalmia is a rare bilateral granulomatous panuveitis that occurs after accidental or surgical injury to 1 eye (the exciting, or inciting, eye) followed by a latent period and development of uveitis in the uninjured globe (the sympathizing eye). The inflammation in the sympathizing eye may occur as early as 9 days or as late as 50 years following the suspected triggering incident. Enucleation of the inciting eye, if blind, is thought to help control inflammation or reduce the risk of inflammation in the other eye.
Histologically, a diffuse granulomatous inflammatory reaction is present within the uveal tract and is composed of lymphocytes and epithelioid histiocytes containing phagocytosed melanin pigment (Figs 12-5, 12-6). Plasma cells are usually scant, suggesting a cell-mediated response. Typically, the choriocapillaris is spared. Varying degrees of inflammation may be present in the anterior chamber, such as collections of histiocytes deposited on the corneal endothelium (mutton-fat keratic precipitates). Dalen-Fuchs nodules, which are collections of epithelioid histiocytes and lymphocytes between the RPE and the Bruch membrane, may be seen in some cases (Fig 12-7). However, Dalen-Fuchs nodules may be present in other diseases, such as Vogt-Koyanagi-Harada syndrome, and thus are not pathognomonic of sympathetic ophthalmia.
Vogt-Koyanagi-Harada syndrome
Vogt-Koyanagi-Harada (VKH) syndrome is a rare cause of posterior or diffuse uveitis and may have both ocular and systemic manifestations. The syndrome occurs more commonly in patients with
Asian or Native American ancestry and usually affects individuals between 30 and 50 years of age.
Figure 12-5 Sympathetic ophthalmia. Diffuse infiltration of the uveal tract by chronic inflammatory cells (arrows). (Courtesy of
Hans E. Grossniklaus, MD.)
Figure 12-6 Sympathetic ophthalmia. A, Diffuse granulomatous inflammation within the choroid. B, Higher magnification shows the presence of multinucleated giant cells (arrowheads). (Courtesy of Hans E. Grossniklaus, MD.)
Figure 12-7 Dalen-Fuchs nodules in sympathetic ophthalmia. A, Focal collections of inflammatory cells are located between the RPE and Bruch membrane (arrows). B, Higher magnification demonstrates the presence of epithelioid histiocytes containing cytoplasmic pigment (arrows) within the nodules. (Courtesy of Hans E. Grossniklaus, MD.)
A chronic, diffuse granulomatous uveitis resembles that seen in sympathetic ophthalmia. However, in VKH, the entire choroid, including the choriocapillaris, tends to be involved by the inflammatory reaction. The granulomatous inflammation may extend to involve the retina. Because the disease is one of exacerbation and remission, chorioretinal scarring and RPE hyperplasia and/or atrophy may also be observed.
Sarcoidosis
Sarcoidosis is a multisystem granulomatous disease characterized by inflammatory nodules, which can occur in various organs and tissues. The uveal tract is the most common site of ocular involvement by sarcoidosis. Anteriorly, inflammatory nodules of the iris may be seen, either at the pupillary margin (Koeppe nodules) or elsewhere on the iris (Busacca nodules). In the posterior segment, chorioretinitis, periphlebitis, and chorioretinal nodules may be seen. Periphlebitis may appear clinically as inflammatory lesions described as candlewax drippings. The optic nerve may be edematous because of inflammatory infiltration.
Histologically, the classic sarcoid nodule is composed of noncaseating granulomas. These are collections of epithelioid histiocytes, sometimes accompanied by multinucleated giant cells, that have a surrounding cuff of lymphocytes (Fig 12-8). Noncaseating refers to the lack of necrosis in the center of the nodule. In the uvea, the inflammatory infiltrate may show a more diffuse distribution of lymphocytes and epithelioid histiocytes (granulomatous inflammation). The multinucleated giant cells may demonstrate asteroid bodies (star-shaped, acidophilic bodies) and Schaumann bodies (spherical, basophilic, calcified bodies). Neither asteroid nor Schaumann bodies are pathognomonic for sarcoidosis.
Juvenile xanthogranuloma
Juvenile xanthogranuloma is an uncommon inflammatory condition that occurs in children. The skin and uvea are commonly affected areas and, in the uveal tract, lesions may present as a solid mass, mimicking a tumor. Histologically, the lesions have a characteristic appearance with the presence of lipid-laden histiocytes, Touton giant cells, lymphocytes, and occasional eosinophils (Fig 12-9). The lesions are often vascularized, and these blood vessels tend to be fragile. This results in intralesional hemorrhage and, in the iris, may result in spontaneous hyphema.
Figure 12-8 Sarcoidosis. A, Gross appearance of multiple discrete nodules on the skin of the upper extremity. B, Histology of sarcoid nodule showing epithelioid histiocytes (between arrowheads) and multinucleated giant cells (arrow). (Part A courtesy of
Curtis E. Margo, MD; part B courtesy of Hans E. Grossniklaus, MD.)
Figure 12-9 Juvenile xanthogranuloma. Touton giant cells (arrow), foamy histiocytes (arrowhead), and lymphocytes are