Aim: Our study aimed to report the normative values for optic nerve diameter in different age groups in MR imaging (MRI) in the pediatric population and to find a cut-off value for diagnosis in different age groups to be used for the diagnosis of optic glioma in patients with Neurofibromatosis 1(NF1). Materials-methods: Orbital MRI obtained from 2011 to 2021 for children with and without NF1 were reviewed. Patients were divided into three groups: NF1 with glioma (group 1, n = 38), NF1 without glioma (group 2, n = 57), and healthy controls (group 3, n = 295). Two radiologists assessed diameter and tortuosity using validated criteria. The optic nerve measurements were obtained by two radiologists in two plans (axial and coronal sections) at five locations; retroocular, midsegment, and prechiasmatic segment on axial plane and retroocular segment and chiasmatic on coronal plane. Results: Optic nerves were divided into 4 age groups: 0–2 years, 2–6 years, 6–12 years, and 12–18 years. It was observed that optic nerve diameters increased with age in healthy individuals. In subjects in groups 1 and 2, the mean diameter of the optic nerve was significantly greater at all locations compared with control individuals. Tortuosity scores were significantly associated in NF1 subjects with optic glioma than in NF1 subjects without optic glioma. Conclusion: We present the normative values obtained by measuring optic nerve diameters in pediatric populations (0–18 years) on MRI of our center. A rapid increase in optic nerve diameter was observed in the first 6 years of life, followed by a slower increase. Quantitative reference values for optic nerve diameter will benefit the development of objective diagnostic criteria for optic nerve gliomas (ONGs) secondary to NF1.