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Uveitis is a complex disorder including both infectious and non-infectious etiologies. Clinical diagnosis is a challenge because many diseases share common clinical signs. Laboratory support is crucial for confirming the clinical diagnosis. Laboratory diagnosis includes direct tests and indirect tests. For example smear, culture, and molecular diagnostics demonstrate the pathogens, hence they are direct tests. Immunologic tests employ an antigen to detect presence of antibodies to a pathogen, or an antibody to detect the presence of an antigen, of the pathogen in the specimens. The immunological tests used in laboratories are made by producing artificial antibodies that exactly "match" the pathogen in question. When these antibodies come into contact with a sample they bind to the matching pathogen if found in the sample. Hence they are grouped under indirect evidence. There are several investigations in uveitis to reach the confirmed diagnosis including microbiological, immunological, imaging and molecular diagnostic testing. In this section we will discuss immunological investigations of infectious and non-infectious uveitis.

A 25-year-old male presented with visual loss in the right eye for 20 days and best-corrected visual acuity of counting fingers in the right eye and 20/20 in the left eye. The anterior chamber (AC) had old keratic precipitates, no AC reaction, dense vitritis, active multifocal retinochoroiditis, and retinal vascular sheathing in all quadrants. The left eye showed sheathed blood vessels with chorioretinal atrophy [Fig. 1]. Figure 1 (a) Color fundus montage of the right eye shows vitritis, vascular sheathing, and retinochoroidal infiltrates. (b) Enlarged view of multifocal retinochoroidal infiltrates with vitreous exudates in the right eye. (c) Color fundus montage of left eye showing ... The regular bacteriologic and viral investigations on the aqueous and vitreous samples were negative. ELISA for HIV 1 and 2 was positive. Rapid plasma regain (RPR) was reactive at a dilution of >1:32, and Treponema pallidum hemagglutination assay (TPHA) was positive at more than 1:1280 dilution [Table 1]. Table 1 Investigations carried out and their results The patient was started on tapering dose of oral steroids (1 mg/kg/day), antiretroviral therapy (tenofovir 300 mg, lamivudine 300 mg, and efavirenz 600 mg once daily). Intramuscular penicillin was administered for 3 weeks (2.4 million units every week). After 2 months, visual acuity improved to 20/30, and vitreous inflammation cleared leaving behind retinal pigment epithelium mottling [Fig. 2]. Figure 2 Color fundus montage picture of the right eye showing resolution of vitritis and retinochoroiditis with retinal pigment epithelium mottling 2 months following initiation of treatment