The traditional bacteriologic diagnostic methods rely on the detection of acid fast bacilli (AFB) by either the Ziehl-Neelsen or the auramine-rhodamine stain. Although roughly 50% of active pulmonary tuberculosis may show smear positivity in sputum samples, the sensitivity of these tests in ocular fluids is low. The IGRAs, though more sensitive than the TST, are still unable to distinguish between latent and active tuberculosis.

Molecular tools such as the nucleic acid amplification tests, PCR and GeneXpert MTB/RIF have emerged as promising tools. They have the added advantage of the ability to detect drug resistance. However, ocular fluid samples availability is usually low, affecting the amount of DNA load and hence the sensitivity and specificity of these assays. Moreover, comparative studies with the gold standard (culture) are still lacking.

Histopathological demonstration of necrotising granulomas in ocular tissue may support the diagnosis of tuberculosis, but in the absence of AFB, the diagnosis of tuberculosis cannot be confirmed. Also, obtaining ocular tissue for histological examination may not be possible in all cases, especially in posterior uveitis.

A reasonable understanding of the available diagnostic tests , particularly their strengths and weaknesses, individualised to the clinical picture, allows for a judicious use of these modalities in a particular clinical setting to achieve a diagnosis (Table 4.1).