MT-ND4 and Leber hereditary optic neuropathy: This is especially the case for unaffected LHON carriers as smoking, and to a lesser extent excessive binge drinking, has been linked with an increased risk of disease conversion.42 It also seems sensible to avoid exposure to other putative environmental triggers for visual loss in LHON, in particular industrial toxins and drugs with mitochondrial-toxic effects, for example ethambutol.1, 2