Ethambutol-Induced Optic Neuropathy: A Retrospective Study of Incidences and Risk Factors

The present study aims to determine the incidences of ethambutol-induced optic neuropathy (EON) and its associated risk factors in Central Indian tertiary care centers.

A single-centered retrospective observational study was conducted. Data was collected from the Directly Observed Therapy Short-course (DOTS) centre after the revised National Tuberculosis Control Program (RNTCP) 2016 guidelines were implemented. The collected data included demographic data, history of underlying diseases, such as diabetes mellitus, hypertension, HIV infection, and history of smoking. The site of tuberculosis infection, daily dose, the duration of ethambutol (EMB) treatment, onset, and type of ocular symptoms were recorded. We performed regression analyses to investigate the univariate and multivariable associations with different variables.

Of the 1676 patients who received ethambutol for TB treatment, 987 had an ophthalmological symptom unrelated to EON, and 13 developed EON (incidence =0.28%). Demographic and clinical variables considered were age, gender, race/ethnicity, body mass index (BMI), and diabetes mellitus status. Examples of current infection information were chronic HIV and other comorbidities uniquely associated with renal function site/type treatment specific dose/duration ethambutol. Longer treatment duration significantly correlates with greater thickness of the left temporal retinal nerve fibre layer (RNFL) and thicker average RNFL. Increased peripapillary retinal nerve fibre layer (pRNFL) thickness on the left nasal RNFL scan was significantly correlated with ethambutol tablets (or count) (p=0.027).

The findings indicate that ethambutol toxicity is indeed dose and duration-dependent, evidenced by the relationship between prolonged treatment and increased RNFL thickness, suggesting heightened risk of visual impairment. Moreover, adverse effects were observed at even lower doses (12.3 mg/kg), reinforcing that no dose of ethambutol is entirely safe.