Ocular tuberculosis (TB) is a form of extrapulmonary tuberculosis where Mycobacterium tuberculosis affects one or both eyes. While rare compared to pulmonary TB, it can be a serious infection affecting various eye structures.
How Tuberculosis Impacts the Eye
Tuberculosis can manifest in the eye through several mechanisms. The bacteria most commonly spread to the eye through the bloodstream from a primary infection site elsewhere in the body, such as the lungs, a process known as hematogenous spread. Less commonly, direct contact with eye structures like the eyelids or conjunctiva can lead to primary ocular involvement. A hypersensitivity reaction to Mycobacterium tuberculosis antigens can also cause inflammation in the eye.
The specific impact of ocular TB depends on which part of the eye becomes affected. Uveitis, an inflammation of the uvea (the middle layer of the eye comprising the iris, ciliary body, and choroid), is a common manifestation, particularly posterior uveitis. This inflammation can present as granulomatous uveitis, characterized by iris granulomas and “mutton-fat” keratic precipitates on the cornea.
Another condition that can arise is choroiditis, an inflammation of the choroid, which is the most vascular tissue of the eye and thus susceptible to bacterial spread. This can lead to the formation of choroidal tubercles, which are small, yellowish lesions, often located in the posterior pole of the eye. Retinal vasculitis, an inflammation of the retinal blood vessels, also occurs, often involving the veins and potentially leading to vitreous infiltrates, retinal hemorrhages, and neovascularization.
Damage to the optic nerve can result in optic neuropathy, which may present as optic nerve edema, papillitis, or optic nerve tubercles. While less frequent, the outer white layer of the eyeball can also experience inflammation, known as scleritis or episcleritis. Tuberculous conjunctivitis, an infection of the conjunctiva, is a rare manifestation but can cause redness, discharge, and the formation of granulomas or nodules.
Identifying Symptoms
The symptoms of ocular TB can be diverse and often resemble those of other eye conditions, making a definitive diagnosis challenging. Symptoms can develop gradually and may affect one eye (unilateral) or both eyes (bilateral).
Blurred or decreased vision is a common symptom. Individuals may also experience eye pain or discomfort, along with redness of the eye. Sensitivity to light, known as photophobia, is another frequent symptom.
Patients might also notice floaters, which are small, dark shapes that appear to drift across the field of vision, or flashes of light. Watering eyes and swelling around the eye are additional symptoms. Some individuals with ocular TB may not experience any symptoms at all.
Diagnosis and Treatment
Diagnosing ocular TB can be complex because its presentation varies widely and often mimics other eye conditions. The diagnostic process begins with a comprehensive eye examination, including a slit-lamp examination to view the front of the eye and fundoscopy to examine the back. Advanced imaging techniques like optical coherence tomography (OCT) or fluorescein angiography may also be used to evaluate the extent of inflammation and structural changes.
A thorough medical history is collected, inquiring about any past exposure to TB, recent travel to areas where TB are common, or a history of systemic TB. Screening for systemic TB is also performed, involving a chest X-ray or CT scan to detect active or latent pulmonary tuberculosis. Blood tests such as Interferon-Gamma Release Assays (IGRAs), including T-SPOT.TB or QuantiFERON-TB Gold, and the Tuberculin Skin Test (TST) are used to assess the immune response to M. tuberculosis. While TST can indicate prior exposure, it may not confirm active infection, and false negatives can occur, especially in disseminated TB.
Sometimes, a sample of fluid from the eye, such as aqueous or vitreous humor, may be analyzed using Polymerase Chain Reaction (PCR) to detect M. tuberculosis DNA. While PCR offers faster results and improved accuracy compared to culture, its sensitivity can vary depending on the ocular disease type. Biopsy of affected eye tissue is rarely performed due to its invasive nature and potential risks, although it is considered the gold standard for definitive diagnosis when M. tuberculosis is isolated. Throughout the diagnostic process, other conditions that present with similar symptoms, such as sarcoidosis or syphilis, must be ruled out.
Treatment for ocular TB follows the same principles as treating systemic tuberculosis. A multi-drug regimen is prescribed, involving a combination of anti-tuberculosis drugs such as isoniazid, rifampicin, pyrazinamide, and ethambutol. The initial phase of treatment includes all four drugs for approximately two months, followed by a continuation phase with rifampicin and isoniazid for an additional four months.
The total duration of treatment is prolonged, lasting from six to nine months, depending on the severity of the infection and the patient’s response to therapy. Completing the full course of medication is important to prevent drug resistance and reduce the likelihood of recurrence. Corticosteroids may be used alongside anti-TB drugs to help reduce inflammation within the eye. However, corticosteroids are administered under close medical supervision and always in conjunction with anti-TB therapy to avoid worsening the infection. Regular follow-up appointments with both an ophthalmologist and an infectious disease specialist are necessary to monitor treatment effectiveness and manage any potential side effects.