Magnetic Resonance Evaluation of Normal Optic Nerve Sheath and Optic Nerve Diameter in Eastern Indian Paediatric Population- A Retrospective Study

Background: Prospective magnetic resonance imaging (MRI) of orbits in healthy paediatric population is difficult as it involves sedation or general anaesthesia in most of the cases. The data of normal value of healthy paediatric optic nerve and optic nerve sheath diameter is also scant in literatures for Indian paediatric population. The normal data will help in defining abnormal optic nerve such as congenital optic nerve hypoplasia, optic nerve atrophy and distended optic nerve sheath in raised intracranial pressure. AIM: The aim of our retrospective study is to define the normal value of optic nerve and optic nerve sheath diameter in MRI of paediatric Indian population. MATERIAL AND METHODS:190 MRI studies of paediatric brain with normal radiology reports and no history of raised intracranial pressure were retrospectively reviewed by two senior radiologists using T2 weighted axial brain images. RESULT: The mean optic sheath diameter and optic nerve diameter of 380 eye balls were 4.746 and 2.59 mm respectively. The age wise distribution of optic sheath diameter and optic nerve diameter were 4.08±0.019, 2.05±0.608 in 0-2-year age group, 4.83±0.575, 2.54±0.456 in 3-6-year age group, 4.789±0.553, 2.704±0.447 in 7-12-year age group, and 4.82±0.567, 2.65±0.412 in 13-18 years age group in mean (mm)±standard deviations respectively. Three hundred seventy-one (97%) optic sheath measurement of the 380 eye balls was below the threshold of 6 mm and about 352 (92%) optic nerve measurements out of 380 globes were having optic nerve thickness above 2 mm. This normative data will help the ophthalmologist, clinician, neuro-ophthalmologist and radiologists for better quantitative evaluation of pediatric patient with vision abnormality.