98th Annual Meeting DOG 2000

P 78

Long Term Reversibility of Ethambutol Optic neuropathy

I. Frisch, A.-L. Castro-Mendoza, H. Krastel

Introduction: As first line antituberculous drug Ethambutol is still irreplaceable. It may cause significant visual impairment: deficiencies in blue green and in red green discrimination, reduced visual acuity, and central scotoma. By decreasing cytosolic calcium and increasing mitochondrial calcium, Ethambutol perturbs mitochondrial function. Ethambutol afflicts retinal ganglion cells and synaptic connections between cones and horizontal cells, thus hampering the color coding process at two levels. There is no entirely safe dosage. Visual side effects have been reported from an intake as low as 15 mg/kg/bw/day, however, application around 20 mg/kg/bw/day is regarded as therapeutically effective. The early Ethambutol visual deterioration is detected, the more favourable are the prospects for reversibility. Long term follow up may pay. We report on two patients who, after severe visual loss, recovered to near normal Snellen acuity during a course of more than one year.

Methods: Acuity was tested following DIN 58220 (linked optotypes). Velhagen and Ishihara pseudoisochromatic plates, saturated (Farnsworth) and desaturated (Lanthony) versions of the Panel D 15 were aplied for colour vision exams. Fields were tested by Goldmann kinetic and / or Octopus static procedures, and VEP was performed according to the ISCEV Standard.

Results: After an uneventful ocular history, a female of 42 years underwent a 4 month treatment with Ethambutol (1800 mg/day) for pulmonary tuberculosis, unless she encounted rapid visual loss. Acuity had dropped to 0.1 OU, field examination revealed central scotomata, an acquired red green defect was recorded by arrangement tests, and VEP latency was delayed. Despite discontinuation of Ethambutol, acuity went down to 1/15 OD and 0.08 OS during the subsequent weeks, 3 months after Ethambutol withdrawal, acuity remained at 0.1 and 0.125, but then slowly recovered towards 0.5 and 0.3 after 7, and to 0.8 and 0.6 after 12 months, parallelled by improvement in colour vision, field and VEP findings. A similar course was observed in another female patient aged 52, needing more than 2 years to restore acuity.

Discussion: If significant visual loss occurs due to Ethambutol, recovery may take more than one year. The possibility of long term recovery has to be considered in judgement of visual functions after Ethambutol toxicity.

Dept. of Ophtalmology, Ruprecht Karls University of Heidelberg, Im Neuenheimer Feld 400. D – 69120 Heidelberg, Germany
Supported by the KAAD