Vol. 43 No. 2 Original Research PDF

Baseline Retinal Nerve Fiber Layer Thickness and Visual Outcomes of Eyes with Ethambutol Toxic Optic Neuropathy

Franz Marie Cruz, MD, DPBO


To determine the retinal nerve fiber layer thickness (RNFL) in eyes with ethambutol-induced toxic optic neuropathy (ETON) at the time of diagnosis and to describe the visual outcomes at 1, 3, and 6 months after discontinuation of ethambutol.


This was a retrospective chart review of 8 patients (15 eyes) diagnosed with ETON that had RNFL thickness measurements using Cirrus® spectral-domain optical coherence tomography (OCT) at the time of diagnosis. Visual function was measured on initial visit and at 1, 3, and 6-month follow-up. Snellen visual acuity was converted to logMAR. Color vision was measured using Ishihara 14-plate test chart.


The mean duration from commencement of ethambutol intake to onset of visual symptoms was 16 weeks (range: 8-24). While, the mean duration from onset of visual symptoms to discontinuation of ethambutol was 4 weeks (range: 2-14). The mean global RNFL thickness at time of diagnosis was 101.2 ± 17.0 microns. Mean RNFL in the temporal, superior, nasal, and inferior sectors were as follows: 79.2 ± 15.4, 119.7 ± 27.9, 71.7 ± 9.2, and 136.7 ± 25.8 microns. Global and sectoral RNFL thicknesses were either normal or thick when compared to age-matched normal database. No eye displayed global or sectoral RNFL thinning. Mean baseline visual acuity and color vision were logMAR 1.2 and 5 plates, respectively. At 1, 3, and 6 months after discontinuation of ethambutol, mean visual acuity and color vision were 0.96 and 6, 0.63 and 11, and 0.44 and 13, respectively.


Patients with early ETON have normal or thick RNFL at time of diagnosis. They display good visual recovery 6 months following discontinuation of ethambutol.

Keywords: Ethambutol, toxic optic neuropathy, optical coherence tomography, retinal nerve fiber layer thickness, ethambutol-induced toxic optic neuropathy