In the present study, regular ophthalmic examinations performed in patients taking ethambutol were analyzed and the risk factors for ethambutol optic neuropathy were investigated.

We retrospectively collected the data of patients diagnosed with tuberculosis at Inje University Sanggye Paik Hospital and referred to the Department of Ophthalmology between October, 2010 and June, 2015. The patients were divided into three groups: group A (patients without visual loss), group B (patients with visual loss who were not diagnosed with ethambutol optic neuropathy), and group C (patients with visual loss who were diagnosed with ethambutol optic neuropathy). We evaluated each patient's glomerular filtration rate, ethambutol daily dosage, duration of ethambutol prescription, change in best corrected visual acuity, Ishihara color test over time, and peripapillary retinal nerve fiber layer thickness based on optical coherence tomography and mean deviation of perimetry.

Group A consisted of 158 patients (86.8%), group B of 12 patients (6.6%), and group C of 12 patients (6.6%). Age was a risk factor for ethambutol optic neuropathy according to logistic regression analysis ( p < 0.001) with a cut-off value of 59.5. In group B, visual acuity showed significant difference ( p < 0.001) and in group C, visual acuity ( p < 0.001) and color vision ( p < 0.001) showed significant differences before and after taking ethambutol. When comparing groups B and C, average and temporal thickness of peripapillary retinal nerve fiber layer were not significantly different but mean deviation of perimetry was significantly different ( p = 0.010).

Elderly patients should be more cautious when taking ethambutol, and color vision test and perimetry are useful diagnostic tools to differentiate patients with ethambutol optic neuropathy from patients with simple visual loss.