The value of laboratory testing in uveitis.

Accurate diagnosis of uveitis is of great importance since the treatment for the various uveitis entities may differ considerably. In a large number of cases the clinical picture is sufficient to make an adequate diagnosis. There are cases in which the diagnosis cannot be made on clinical grounds alone and support is needed from laboratory tests. Only a limited number of tests have been proven to be useful as a diagnostic or prognostic aid. These include HLA-B27 typing in patients presenting with anterior uveitis and testing for angiotensin converting enzyme and lysozyme in case of suspected sarcoid uveitis. Toxoplasma serology is only useful to exclude the diagnosis and a positive test has very low specific value. Analysis of local intraocular antibody production is a valuable tool to confirm a suspected clinical diagnosis in uveitis. It is now possible to analyse paired serum and aqueous samples for the presence of specific antibodies against toxoplasma, cytomegalovirus, herpes simplex virus and varicella zoster virus using commercially available kits. Of the patients retrospectively diagnosed as having toxoplasma chorioretinitis 75% were shown to have a positive antibody coefficient indicating specific intraocular antibody production. Local antibody production in the eye directed against CMV confirmed the suspected diagnosis of CMV retinitis in 50% of the AIDS patients investigated. Until now we have not been able to measure local antibody production against herpes simplex virus (26 samples tested). Two of three patients with acute retinal necrosis had a positive antibody coefficient against varicella zoster virus. Both of these patients even had a higher titre in the aqueous than in serum. Since the choice of treatment, in infectious uveitis, depends on the causative organisms, it is very important to confirm a suspected clinical diagnosis with aqueous humor analysis.