This review article provides an update on the methods diagnosing ocular tuberculosis (TB), the difficulties in making the diagnosis and makes recommendations to a more accurate diagnosis by combining the available diagnostic tests. Today ocular TB remains a presumptive clinical diagnosis based on positive tuberculin skin test (TST), interferon gamma release assay (IGRA), or chest X-Ray findings suggestive of pulmonary TB. The gold standard tests for diagnosing ocular TB are often not useful, e.g. mycobacterium TB cultures (which require six weeks to process), acid fast bacilli smears or polymerase chain reaction (PCR) detection of MTB DNA samples from ocular samples (low sensitivities). It is noteworthy that the majority of patients with ocular TB have normal chest radiographs without associated pulmonary TB infection. Currently the diagnosis of TB is made using the Mantoux TST which has limited specificity (66%) and sensitivity (71%) due to false positives in patients with non-tuberculus Mycobacterium or previous BCG vaccination. It is also susceptible to false negative results in immunocompromised patients, diabetes, renal disease, young children, elderly and psoriasis. The recommended cut-off for the diagnosis depends on the endemicity of TB, e.g. in countries with higher incidence of TB a higher cut-off is taken. Two commercially available IGRA are used: QuantiFERON Gold (ELISA measuring secreted IFN-gamma) and T-SPOT.TB (T cell based enzyme ELISPOT). According to the authors there is growing evidence that IGRAs are more specific / accurate for the diagnosis of TB than TST which may prevent unnecessary anti-TB treatment. Τhe combination of an IGRA with TST is the most cost-effective model. The diagnosis of ocular TB in non-endemic countries is more difficult than in countries where the disease is endemic. The IGRA tests may need to be interpreted differently. Most clinicians practice with “intention to test as intention to treat”. False positive results are possible in non-endemic regions especially if only one test is used. Presumed diagnosis of ocular TB based on response to treatment may also be difficult in non-endemic regions. The clinical features making ocular TB a likely diagnosis in an endemic country may not be relevant in a non-endemic country. No specific ocular TB clinical pattern was observed in series of patients from European countries. Occlusive vasculitis was the commonest ophthalmologic presentation and serpiginoid choroiditis a marker for ocular TB in England.

Diagnosis of ocular tuberculosis.
Ang M, Vasconselos-Santos D, Sharma K, et al.
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Nikolaos D Georgakarakos

Moorfields Eye Hospital, London, UK.

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