Dr. Rupesh Agarwal
New Delhi, January 15-Tuberculosis (TB) still represents a global health challenge. According to the WHO (World Health Organization) Global TB Report 2019, TB is one of the top 10 causes of death worldwide and the leading cause of death from a single infectious agent, with one third of the world’s population infected with the agent, and thus at risk of developing the disease.
Around 30 high-TB burden countries account for almost 90% of world’s cases and contribute to difficulties in its eradication, including Asian countries like India, Nepal, Singapore and Malaysia. The disease is caused by Mycobacterium tuberculosis, which is spread person-to-person by aerosolized particles when people sick with TB expel mycobacteria into the air by cough.
Most people think that TB is a disease affecting only the lungs, but it can cause disease in multiple organs throughout the body, including the eye.
Ocular TB is a rare extrapulmonary form of the disease, not to be underestimated considering its potential impact on visual loss in patients diagnosed with the disease.
Ocular TB can affect any part of the eye, i.e. it can be intraocular, superficial or periocular, but the most common manifestation is uveitis, an inflammation of the middle layer of the eye, called the uvea. Among all causes of intraocular inflammation, symptoms and clinical features of ocular TB are not specific for the disease and that poses a significant diagnostic challenge, especially because in most cases the disease is confined to the eye in the absence of any findings throughout the body.
Ocular symptoms can be monolateral or bilateral, and include pain, redness, light sensitivity, blurred vision, floaters, and decreased vision, but patients can also be asymptomatic. Ocular TB is usually suspected based on clinical signs, and the diagnosis is further supported by laboratory investigations.
Different tests are performed to check for previous exposure to mycobacterium. In most cases healthy people infected with mycobacterium have body’s natural defences, namely the immune system, that contain the spread of the infection, leading to what is called latent infection. People with latent TB carry the disease and don’t have any symptoms, but they are at risk to develop active disease during their lifetime, including ocular manifestations.
Tuberculin skin test and, more recently, interferon-gamma release assays, including Quantiferon Gold, are widely use to test for exposure to mycobacterium, giving positive results in both latent and active disease. These tests, together with chest Xray, which looks for changes suggestive of TB in the lungs, help achieve the diagnosis in selected patients with clinical pictures suggestive of ocular TB. The disease is curable, and a prompt diagnosis with early treatment can address the infection at an early stage, avoiding damages to sight.
Treatment for ocular TB is the same as for pulmonary TB, consisting of a multi-drug regimen with 4 antimicrobial drugs, and is often managed with the help of a pulmonologist or an infectious disease specialist. Ocular TB is curable and severe visual loss can be prevented when medications are taken properly.
(The writer is Consultant Ophthalmologist at National Healthcare Group Eye Institute, Tan Tock Seng Hospital, Singapore.)