Ethambutol Optic Neuropathy

Paul D. Chamberlain; Ama Sadaka; Shauna Berry; Andrew G. Lee


Curr Opin Ophthalmol. 2017;28(6):545-551. 

In This Article

Clinical Presentation

Patients presenting with EON typically complain of subacute, bilateral, painless, and typically symmetric loss of central vision. Patients may describe cloudy or blurry vision, difficulty reading, difficulty distinguishing colors, or frequent changes in eyeglass or contact lens prescription.[4] Unlike other more commonly known visual toxicity agents (e.g. hydroxychloroquine), where long durations of therapy are required for toxicity, EON may begin rapidly between 1 month and 36 months after beginning therapy. In general, however, most patients experience visual symptoms within the first 9 months of treatment.[4,5,7] In more than 60% of patients, physical examination reveals bilateral, painless, and typically symmetric loss of visual acuity as well as abnormal color vision. Color vision loss is typically in distinguishing green and red, though blue–yellow color changes may also occur.[4,5,22–24] Initially the optic nerve is normal but eventually optic disc pallor will develop. If optic atrophy is present at onset, it is generally considered to be a poor prognostic sign.[4] Visual field testing most often reveals central or cecocentral scotoma,[4,7,25] though bitemporal break out of the visual field defect with optic chiasm involvement has also been reported (see Figure 1).[26–29] Visually evoked potentials (VEP) may reveal abnormalities in the amplitude or latency of the p100 wave.[4,30,31,32]

Figure 1.

Humphrey visual field with foveal threshold of 26 decibels showing bitemporal hemianopsia representing toxicity of the optic chiasm.