Abstract
Purpose: :
The purpose of this study was to investigate various visual function tests for early detection of ethambutol induced ocular toxicity.
Methods: :
A prospective study was conducted on 20 eyes of 10 patients under ethambutol treatment. Visual acuity, visual field, color vision, dilated fundus examination, contrast sensitivity, optical coherence tomography (OCT), and pattern-visual evoked potential (VEP) were assessed. Examinations were conducted prior to therapy and regularly each month through a 5 month period after the initial treatment. VEP assessments were carried out every other month. The mean values for each parameter from each month were compared to baseline examinations to determine differences; where a p-value of < 0.05 was considered significantly different. It was determined that changes in values for each parameter greater than 2 standard deviations (SD) from mean values at baseline were considered "ocular toxicity-induced changes" for each individual eye.
Results: :
Visual acuity, color vision, fundus, contrast sensitivity, and visual field were not affected in any patients. After 4 months of therapy, OCT detected a significant increase in the mean of average retinal nerve fiber layer thickness. Pattern-VEP showed an increased in the mean latency of the P100 wave after 2 and 4 months of therapy. No "ocular toxicity induced changes" were observed in each individual eye using OCT, however, 6 eyes showed "ocular toxicity induced change" through VEP.
Conclusions: :
Pattern-VEP is a more sensitive test for detecting early toxicity than OCT. VEP should be considered when identifying patients who are likely to develop clinical toxicity.
Keywords: drug toxicity/drug effects • image processing • visual impairment: neuro-ophthalmological disease