Analysis of Peripapillary Vessel Density in Ethambutol-induced Optic Neuropathy Using Optical Coherence Tomography Angiography

Purpose: To investigate the changes in peripapillary and macular vessel density in ethambutol-induced optic neuropathy using optical coherence tomography angiography (OCTA). Methods: The medical records of patients diagnosed with ethambutol-induced optic neuropathy were analyzed retrospectively. Patient age, sex, daily dose (mg/day/kg), treatment duration, best-corrected visual acuity (logMAR), color vision (Ishihara color plate tests), and mean deviation of visual field test were evaluated in non-pathological individuals with age and sex controlled as the normal control group. Peripapillary retinal nerve fiber layer (RNFL) thickness, macular ganglion cell/inner plexiform layer (GC/IPL) thickness, radial peripapillary capillary (RPC) density, and macular superficial capillary plexus (SCP) density were also compared between the patient and control groups. Results: The study included 22 patient eyes and 31 control group eyes. Comparing the OCTA results between the groups, there were no significant differences in peripapillary RNFL thickness, but the temporal RPC density was significantly (p = 0.025) lower in the patient group (48.00 +/- 8.23%) than in controls (52.39 +/- 5.58%). For macular structures, the mean GC/IPL thickness and whole SCP density were lower in the patients (p = 0.001 and p = 0.008, respectively). In the patients, the changes in peripapillary RNFL thickness and RPC density were significantly positively correlated (r = 0.811, p < 0.001), as were the mean macular GC/IPL thickness and whole SCP density (r = 0.445, p = 0.037). Conclusions: Patients with ethambutol-induced optic neuropathy had significantly lower temporal RPC and macular SCP densities. Ethambutol toxicity may affect not only axonal degeneration but also peripapillary and macular vascular function.