Early Stage Ethambutol Optic Neuropathy: Retinal Nerve Fiber Layer and Optical Coherence Tomography

Abstract

To evaluate retinal nerve fiber layer (RNFL) thickness with optical coherence tomography (OCT) in early stage ethambutol optic neuropathy. The RNFL thickness of 20 eyes of 10 patients who developed optic neuropathy after taking ethambutol and visited within 6 months after onset were analyzed and compared with those of 54 eyes of 29 healthy age-matched controls. The mean age was 67.40+/-10.25 years for the patients with toxic optic neuropathy and 66.78+/-10.60 for the control group (p=0.948). A full ophthalmologic examination including RNFL evaluation with fast RNFL thickness (3.4) scanning using a Stratus OCT (Carl Zeiss Meditec, Dublin, CA) was performed. RNFL thicknesses associated with early ethambutol optic neuropathy were as follows: temporal 75.35+/-15.77 microm, superior 124.05+/-24.62 microm, nasal 75.15+/-24.23 microm, inferior 127.60+/-22.91 mum, and the average was 100.83+/-16.56 microm. There was no significant difference between the RNFL thickness of the patients with the early stage of ethambutol optic neuropathy and those of the control group. The thickness of RNFL was greater in the temporal quadrant than the nasal quadrant, although not statistically significant. RNFL thickness associated with ethambutol optic neuropathy during the early stages was no different from the controls. Although not statistically significant, the relative thickening of temporal RNFL in our patients might represent a mild swelling of the papillomacular bundle.