Ethambutol retinal toxicity: an electrophysiologic study.
OBJECTIVE
In animal studies, ethambutol (EMB) has been shown to be toxic to cone pedicles and to cause their degeneration in the retinas of fish. The purpose of this study was to determine whether EMB is toxic to retinas in humans.


METHODS
Twenty-seven patients with EMB-induced optic neuropathy and 20 normal control subjects were included in this study. The following details were recorded: age, sex, and systemic condition of the patients, daily dosage of EMB, duration of EMB treatment, visual function at the time of electrophysiologic investigation, time from the onset of blurred vision to the discontinuation of EMB treatment (symptom duration), and time from termination of EMB treatment until electrophysiologic investigation.


RESULTS
The electroretinograms were normal in 25 patients. Twelve patients had normal electro-oculogram (EOG) findings in both eyes and the remaining 15 patients had abnormal EOG findings in at least one eye. Ten eyes showed supranormal EOG (light/dark (L/D)) ratios of more than 2.33, and 13 eyes had decreased L/D ratios (< 1.65). The symptom duration was shorter in the supranormal EOG group.


CONCLUSIONS
The results suggest that a supranormal EOG may be indicative of an early toxic state during EMB therapy and that EMB may cause dysfunction of the retinal pigment epithelium.
Yen
M Y
MY
Department of Ophthalmology, Taipei Veterans General Hospital, National Yang-Ming University, Taipei, Taiwan.
Wang
A G
AG
Chiang
S C
SC
Liu
J H
JH
D000328:Adult; D000368:Aged; D000995:Antitubercular Agents / Q000009:adverse effects*; D004585:Electrooculography; D004596:Electroretinography; D004977:Ethambutol / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012160:Retina / Q000187:drug effects* / Q000502:physiology; D012189:Retrospective Studies
D000995:Antitubercular Agents; D004977:Ethambutol