Ethambutol-associated Optic Neuropathy

INTRODUCTION: Ethambutol is used in the treatment of tuberculosis, which is still prevalent in Southeast Asia, and can be associated with permanent visual loss. We report 3 cases which presented with bitemporal hemianopia. CLINICAL PICTURE: Three patients with ethambutol-associated toxic optic neuropathy are described. All 3 patients had loss of central visual acuity, colour vision (Ishihara) and visual field. The visual field loss had a bitemporal flavour, suggesting involvement of the optic chiasm. TREATMENT: Despite stopping ethambutol on diagnosis, visual function continued to deteriorate for a few months. Subsequent improvement was mild in 2 cases. In the third case, visual acuity and colour vision normalised but the optic discs were pale. OUTCOME: All 3 patients had some permanent loss of visual function. CONCLUSIONS: Ethambutol usage is associated with permanent visual loss and should be avoided if possible or used with caution and proper ophthalmological follow-up. The author postulates that in cases of ethambutol associated chiasmopathy, ethambutol may initially affect the optic nerves and subsequently progress to involve the optic chiasm.