Decreased Retinal Nerve Fiber Layer Thickness detected by Optical Coherence Tomography in Patients with Ethambutol-induced Optic Neuropathy

Abstract

Purpose: It is difficult to assess the degree of optic nerve damage in patients with ethambutol-induced optic neuropathy, especially just after the onset of visual loss, when the optic disc typically looks normal. This study aims to evaluate changes in retinal nerve fiber layer thickness (RNFLT) using optical coherence tomography (OCT) in patients with optic neuropathy within three months of cessation of ethambutol therapy.

Methods: Retrospective observational case series from a single neuro-ophthalmology practice. Eight patients with a history of ethambutol-induced optic neuropathy were examined within 3 months after stopping ethambutol. All patients underwent a neuro- ophthalmologic examination including visual acuity, color vision, visual fields, and funduscopy. OCT was performed on both eyes of each patient using the retinal nerve fiber layer analysis protocol.

Results: The interval between cessation of ethambutol therapy and the initial visit ranged from 1 week to 3 months. All patients had visual deficits characteristic of ethambutol-induced optic neuropathy at their initial visit, and the follow-up examination was performed within 12 months in all patients. Compared to the initial RNFLT, there was a statistically significant decrease in the mean RNFLT of the temporal, superior, and nasal quadrants (P = 0.009, 0.019, 0.025, respectively), with the greatest decrease in the temporal quadrant (mean decrease = 26.5 μ).

Conclusions: There is a decrease in the RNFLT in all quadrants in patients with ethambutol-induced optic neuropathy who have recently discontinued the medication. This decrease is most pronounced in the temporal quadrant of the optic disc.