We labeled a patient to have ocular TB in this study based on the proposed diagnostic criteria for presumed ocular TB by Gupta et al.  (i.e., a known clinical sign of ocular TB with a positive systemic finding such as a tuberculous lesion on CXR). Though the PCR result done in one of the seven labeled to have POTB was negative, it still does not rule out possible ocular TB, only having a reported maximal sensitivity of 66.6% .
Ocular TB is one manifestation of EPTB. It can adversely affect the quality of life of people by threatening vision. Of the 103 pulmonary TB patients in the study, seven (6.8%) showed signs of ocular inflammation. There are probably more cases we were unable to detect because we did not examine EPTB patients. This rate is higher than the 1.39% to 1.46% ocular involvement found in other studies [6, 9]. It can expand the knowledge base regarding the epidemiology of POTB and can contribute to greater awareness on the condition.
Ocular TB is not easy to diagnose because most of the time there is no concurrent active systemic TB. Notable in our findings was the unilateral presentation of all patients labeled as POTB, concurring with the reports of some authors that ocular TB is usually unilateral . However, the absence of a single manifestation of POTB further compounds the difficulty in recognizing the disease. In our study, as with other reports , posterior segment lesions were the predominant finding in patients with POTB. This would be a logical finding in our diagnosed PTB patient population since choroidal tubercles and retinal vasculitis indicate hematogenous seeding of bacilli. EPTB mainly results from reactivation of a tuberculous focus after hematogenous dissemination or lymphogenous spread from a primary, usually pulmonary, focus .
The amount of TB burden necessary in the lungs to produce EPTB has not yet been quantified. TB affects other sites of the body other than the lungs and eyes. One recently published study found that among the total of 2,161 TB infection cases, 705 (32.6%) were EPTB, 1,186 (54.9%) were PTB, 106 (4.9%) were disseminated TB, and 164 (7.6%) were concurrent EPTB-PTB. Most common sites of EPTB they found were in pleural (41.1%) and lymphatic (30.6%) tissues followed by genitourinary (7%), bone/joint (5.8%), cutaneous (4.5%), meningeal (4.1%), peritoneal (2.6%), and gastrointestinal (2%) . In our study, we incidentally detected two cases of cervical lymphadenopathy out of the seven detected POTB cases.
One study conducted a multivariate analysis determining risk factors for developing EPTB relative to PTB, and they found that female gender and older age are associated with EPTB . Our male POTB patients outnumbered the females (4:3). However, we found a relatively higher mean age in our POTB cluster, with six of the seven patients belonging to the 41- to 70-year-old age group. We found the mean age of those with POTB higher (60.00 ± 13.760 years old) than those without ocular findings (50.93 ± 17.406 years old). One East Asian study found increasing longevity of their population and the high rate of TB in their elderly as important factors contributing to their persistent high rate of TB . Old age has indeed been cited to be a risk factor for EPTB since the immune system can be weaker in the elderly [16, 18].
The study is limited by a lack of investigations such as fluorescein angiography, indocyanine green angiography, or ocular coherence tomography. Confounders that compromise the immune system were not controlled in the analysis (e.g., DM, HIV). Effect modifiers such as cataract were not controlled. Future studies could look at the clinical/radiological spectrum of PTB cases associated with POTB. Since active PTB can easily be genotyped, genotypic profiling of these cases can also be done.