Decreased retinal nerve fibre layer thickness detected by optical coherence tomography in patients with ethambutol-induced optic neuropathy.

Background: 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.

Aim: To evaluate changes in retinal nerve fibre layer thickness (RNFLT) using optical coherence tomography (OCT) in patients with optic neuropathy within 3 months of cessation of ethambutol treatment.

Design: A retrospective observational case series from a single neuro-ophthalmology practice.

Methods: 8 patients with a history of ethambutol-induced optic neuropathy were examined within 3 months after stopping ethambutol treatment. All patients underwent a neuro-ophthalmologic examination, including visual acuity, colour vision, visual fields and funduscopy. OCT was performed on both eyes of each patient using the retinal nerve fibre layer analysis protocol.

Results: The interval between cessation of ethambutol treatment 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. Compared with 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 and 0.025, respectively), with the greatest decrease in the temporal quadrant (mean decrease 26.5 mum).

Conclusions: A decrease in RNFLT is observed 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.