Delayed Visual Recovery from Severe Ethambutol Optic Neuropathy in Two Patients with Atypical Mycobacterium Infection

Two patients with atypical mycobacterium infection developed severe ethambutol optic neuropathy for a long period of time followed by good recovery. A 74-year-old female (Case 1) developed reduced visual acuity of 20/200 OD and 20/400 OS after oral administration of ethambutol for 14 months, and ethambutol was discontinued. A 63-year-old female (Case 2) developed a visual acuity of CF10' OD and 20/400 OS after oral administration of ethambutol for 10 months, and ethambutol was discontinued. Cases 1 and 2 had anemia after having undergone gastrectomy 10 years or 5 years earlier, respectively, and both had rheumatoid arthritis. At the onset of ethambutol optic neuropathy, both patients developed severe bilateral visual loss with bitemporal hemianopia-like visual field disturbance. However, Cases 1 and 2 did not show disc pallor nor nerve fiber layer defect (NFLD) at any time during the follow-up period, and had good recovery in visual function at 18 months or 19 months after the onset of optic neuropathy, respectively. In patients with severe ethambutol optic neuropathy, as long as disc pallor and NFLD are not observed, good visual recovery may be expected even if severe visual loss persists for a long period of time.