Background Optic neuritis (ON) is the most prevalent manifestation of pediatric multiple sclerosis (MS ped ) and myelin-oligodendrocyte glycoprotein antibody-associated disease (MOGAD ped ) in children > 6 years. In this study, we investigated retinal atrophy patterns and diagnostic accuracy of optical coherence tomography (OCT) in differentiating between both diseases after the first ON episode. Methods Patients were retrospectively identified in eight tertial referral centers. OCT, VEP and high/low-contrast visual acuity (HCVA/LCVA) have been investigated > 6 months after the first ON. Prevalence of pathological OCT findings was identified based on data of 144 age-matched healthy controls. Results Thirteen MOGAD ped (10.7 ± 4.2 years, F:M 8:5, 21 ON eyes) and 21 MS ped (14.3 ± 2.4 years, F:M 19:2, 24 ON eyes) patients were recruited. We observed a significantly more profound atrophy of both peripapillary and macular retinal nerve fiber layer in MOGAD ped compared to MS ped (pRNFL global: 68.2 ± 16.9 vs. 89.4 ± 12.3 µm, p  < 0.001; mRNFL: 0.12 ± 0.01 vs. 0.14 ± 0.01 mm 3 , p  < 0.001). Neither other macular layers nor P100 latency differed. MOGAD ped developed global atrophy affecting all peripapillary segments, while MS ped displayed predominantly temporal thinning. Nasal pRNFL allowed differentiation between both diseases with the highest diagnostic accuracy (AUC = 0.902, cutoff < 62.5 µm, 90.5% sensitivity and 70.8% specificity for MOGAD ped ). OCT was also substantially more sensitive compared to VEP in identification of ON eyes in MOGAD (pathological findings in 90% vs. 14%, p  = 0.016). Conclusion First MOGAD-ON results in a more severe global peripapillary atrophy compared to predominantly temporal thinning in MS-ON. Nasal pRNFL allows differentiation between both diseases with the highest accuracy, supporting the additional diagnostic value of OCT in children with ON.