Retinal nerve fiber layer thickness and central macular thickness in patients with ethambutol optic neuropathy: a prospective analysis by optical coherence tomography

Background Ethambutol, a key drug for tuberculosis (TB) treatment, poses a risk of ethambutol optic neuropathy, that potentially leads to irreversible visual loss. Early detection is crucial to prevent long-term impairment. Objective This study aimed to evaluate the changes in retinal nerve fiber layer (RNFL) thickness and macular thickness in patients receiving ethambutol for newly diagnosed pulmonary TB. Patients and methods This is a prospective observational study that was conducted on 96 pulmonary TB patients aged 18–60 years at Sri Venkateswara Ramnarayan Ruia Govt. General Hospital (SVRRGH), Tirupati, India under the National Tuberculosis Elimination Program (NTEP). Comprehensive ophthalmic evaluation, including visual acuity, contrast sensitivity, color vision, and spectral-domain optical coherence tomography were performed at baseline, and at 2, 4, and 6 months after starting ethambutol treatment. Results Among 192 eyes, the mean baseline best-corrected visual acuity was 0.26±0.20 LogMAR. It significantly worsened to 0.42±0.31 LogMAR by the 6th month after treatment ( P <0.0001), particularly in those on higher ethambutol doses. In addition, contrast sensitivity declined significantly by 6 months ( P =0.048). Color vision abnormalities developed, with 12.5% of the patients exhibiting red–green defects, 19.8% blue–yellow defects, and 3.1% mixed abnormalities, with the highest dose group (group IV) showing the most pronounced changes ( P =0.03). The average RNFL thickness decreased in all quadrants except the nasal quadrant, with the inferior quadrant being most affected, particularly in the higher dose group ( P <0.001). The mean central macular thickness at baseline was 257.3±20.3 μm. At the 4-month follow-up, it significantly decreased to 243.8±36.9 μm ( P =0.04), and was further reduced to 232.4±45.5 μm at 6 months ( P <0.001). Conclusion The reduction in RNFL and macular thickness indicates ethambutol harmful effects on the optic nerve, reinforcing the importance of regular ophthalmic monitoring using optical coherence tomography. Comprehensive visual assessments should be a part of the standard care protocol for patients on ethambutol therapy to prevent irreversible visual loss.