Pathogenesis and Pathology of Intraocular Tuberculosis

Intraocular tuberculosis (TB) is an extremely paucibacillary form of extrapulmonary TB. It likely results from bacterial dissemination to the eye from lungs, localization in ocular tissues, followed later by reactivation and appearance of clinical signs. These have been partly demonstrated in the guinea pig model of ocular TB. Alternative hypotheses have been suggested but are not supported by adequate evidence. Mycobacterial recognition by macrophages and dendritic cells probably leads to activation of several immune pathways, primarily the Th1 and Th17 pathways, as in other TB infections. Histopathology of bacteriologically proven ocular TB tissues reveals granulomatous inflammation with central caseous necrosis containing occasional acid-fast organisms. Recent reports have also demonstrated intraretinal granuloma in the vicinity of retinal vessels and T-cell infiltration of epiretinal membranes, in cases of TB retinal vasculitis.