Ganglion Cell Layer and Inner Plexiform Layer as Predictors of Vision Recovery in Ethambutol-Induced Optic Neuropathy: A Longitudinal OCT Analysis

Purpose: To describe changes in the retina during ethambutol-induced optic neuropathy (EON) progression, and determine the retinal layer thickness as a predictive factor for vision recovery after stoppage of ethambutol (EMB) in EON. Methods: A total of 42 eyes in 21 patients with EON underwent Spectralis optical coherence tomography after the onset of symptoms. Peripapillary and macular retinal nerve fiber layer as well as ganglion cell layer plus inner plexus layer (GCIPL) thickness was measured using Early Treatment Diabetic Retinopathy Study (ETDRS) circles. Data on best-corrected visual acuity at first visit and 1, 3, 6, and 12 months after stoppage of drug were collected. The longitudinal change of each retinal layer was described, and the association between retinal thickness at the first visit and the degree of vision recovery at each visit was analyzed. Results: In inner temporal GCIPL, a 10-μm-thickness loss in the initial OCT was associated with a 0.5 decrease in the amount of logMAR visual acuity recovery at 12 months (P < 0.001, 95% confidence interval [CI]: 0.2-0.7), and a 10-μm-thickness reduction between follow-up visits was associated with a 0.5 decrease in the amount of logMAR visual acuity recovery (P < 0.001, 95% CI: 0.3-0.7). Conclusions: We described a structure-function relationship between the retinal changes that occur in early EON and vision recovery. Temporal GCIPL could be used to predict vision recovery at 12 months after stoppage of EMB. Careful evaluation for GCIPL damage is required for visual prognosis in early EON.