CHAPTER 5

Uveal Tract and

Ocular Inflammation

Iris

IRIS ANATOMY (FIG. 5–1) Dimensions: 12 mm diameter, 37.5 mm circumference (length of Schlemm’s canal); root of iris 0.18 mm thick, midstroma 0.5 mm; thickest at collarette. Radial vessels run from the major arterial circle at the root from two long posterior ciliary arteries and seven anterior ciliary arteries, with a minor circle under the collarette. Surface anatomy from outside in: peripheral crypts, ciliary iris, collarette, Fuchs’ crypts, and pupil. Anterior iris has melanocytes, fibroblasts, and capillaries (increased with rubeosis or pseudorubeosis from iritis). Stroma is composed of collagen, GAG ground substance, channels, and clump cells (macrophages). Stromal pigmentation (neural crest origin) gives iris color, and resident melanocytes are postmitotic and not reactive like the RPE (thus the patency of PI). The iris is an extension of the choroid, which is attached to the sclera only at the vortex vein ostia (the cause of the cloverleaf pattern seen with choroidal effusions) and at the scleral spur.

The iris dilator and sphincter muscles arise from the IPE. The dilator has sympathetic innervation that also stimulates pigmentation (thus, congenital Horner’s syndrome has light-colored irides). The sphincter muscle has cholinergic innervation. Fuchs’ and Michel’s spurs connect the sphincter and dilator muscles; thus, when the iris contricts, it stretches the dilator muscle and vice versa. The iris constrictor shortens by 80% (unusual for a muscle) and thus needs crypts to allow for increased movement.

Iris pigment epithelium (IPE): bilayer of anterior nonpigmented epithelium and posterior pigmented cells are in an apical-to-apical arrangement (like the ciliary body). Iris cysts form if the apical junction breaks down. Poor iris dilation is seen in patients with PXS from basement membrane material deposited into the muscle. Histopathologically, lacy vacuolization represents glycogen deposits seen in diabetic patients.

IRIS COLOBOMA Usually inferonasal.

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174 UVEAL TRACT AND OCULAR INFLAMMATION

IRIS MELANOMA Concern for melanoma if pigmented iris lesion is >2 mm. Increased risk of metastatic cancer increases with age, increased IOP, tumor in angle, extraocular extension, and prior surgery, but not the type of cells seen on pathology. There is a 5% risk of metastatic cancer at 10 years.

IRIDODIALYSIS Tear in root of iris; distinguish from coloboma (which is inferonasal and has the sphincter involved).

IRIDOSCHISIS Seen in elderly patients, with bilateral inferior iris stomal ‘‘shredding’’ and atrophy, which may obstruct the TM and cause glaucoma.

Uveitis

DEFINITION AND CLASSIFICATION Uveitis is broadly defined as inflammation of the uveal tract (iris, ciliary body, and choroid). The definition is complicated by other types of intraocular inflammation (e.g., infections, endophthalmitis, or toxoplasmosis retinitis that spills over to the choroid). Thus, defining the uveitic diseases involves careful classification as to the primary tissue that is affected. In this chapter, the uveitic diseases are classified as anterior (involving the iris and anterior segment primarily), intermediate (involving the pars plana and anterior vitreous primarily), posterior (involving the choroid and retina primarily), and panuveitis (diffuse inflammation of ocular tissues). Uveitis can further be classified by the histopathologic characteristics of granulomatous or nongranulomatous types of inflammation. Further delineation of the inflammation can be made as to whether it is a local ocular disease process only or part of a systemic disease. Thus, a careful history and a review of systems are important first steps in elucidating the etiology of the patient’s inflammation.

GOALS OF THERAPY Suppress the inflammation and prevent secondary complications. Ten percent of cases of blindness in the United States are caused by uveitis complications.

Complete elimination of all active inflammation and cells: most important therapeutic goal, because allowing chronic, even low grade (1 þ cells), uveitis eventually produces permanent structural damage, such as chronic macular edema with cyst or macular hole formation, cyclitic membrane formation with hypotony, and ON damage.

Limitation of total steroid used: long-term use of corticosteroids has a 100% incidence of significant undesirable side effects.

Tables 5–1 and 5–2 present diagnostic uveitis laboratory tests, and associations between uveitis and human leukocyte antigens (HLA).

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UVEITIS 175

TABLE 5–1

Selected Diagnostic Uveitis Laboratory Tests

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