Patients with endogenous intermediate uveitis, posterior uveitis, and panuveitis may present diagnostic dilemmas for the retinal and ocular inflammatory specialist. The differential diagnosis for some of these conditions is vast but may include infectious, inflammatory, and neoplastic conditions, some of which may have vision- or life-threatening consequences. Although an array of laboratory and serological tests are available to assist in the diagnosis, some conditions (ie, intraocular lymphoma) require a tissue diagnosis via a vitreous or chorioretinal biopsy. Infectious uveitides may be diagnosed by routine Gram stain and culture techniques of vitreous fluid in some cases; however, antibody- and polymerase chain reaction-based tests are also available and extremely valuable for the diagnosis of infectious entities, which are slow growing or difficult to culture (viruses, mycobacteria, toxoplasmosis). Understanding the currently available tests for vitreous fluid, the parameters for vitreous fluid collection, and the need for communication with an expert ophthalmic pathologist is essential in clinching the diagnosis. Advances in vitrectomy instrumentation and the advent of small-gauge (23- and 25-gauge) vitrectomy techniques will likely aid the treating physician in obtaining vitreous and chorioretinal biopsy specimens in the future.
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