title: The role of magnetic resonance imaging in diagnosing optic nerve hypoplasia.
abstract: OBJECTIVE
  To establish objective lower limits of normal optic nerve (ON) size in children based on high-resolution orbital magnetic resonance imaging (MRI).
  
  
  METHODS
  Case-control study of patients with ON hypoplasia vs normal controls.
  
  
  METHODS
  A neuroradiologist made 4 measurements of each ON at 2 locations (5 mm posterior to the optic disc and just posterior to the optic canal) in patients with ON hypoplasia and controls aged 0-17 years from an academic eye center and children's hospital. Primary analyses were performed using mixed linear models.
  
  
  RESULTS
  Measurements were made in 26 cases of clinically confirmed ON hypoplasia and 31 controls (median age: ON hypoplasia, 1 year; controls, 5.5 years). Nine of 26 cases (35%) and 19 of 31 controls (61%) underwent high-resolution T2-weighted imaging of the orbits. Mean ON diameter was 1.36 mm (95% CI: 1.19-1.54; P < .001) smaller for clinically hypoplastic ONs than for controls. Optic nerve diameter increased by 0.05 mm per year of age (95% CI: 0.03-0.07; P < .001). A lower bound to the 95% prediction interval for normal optic nerves was (2.24 mm + 0.052 × [age in years]) mm and excluded all but 1 case.
  
  
  CONCLUSIONS
  Age was independently associated with normal ON size by MRI and should be taken into consideration when evaluating ON hypoplasia, based on MRI criteria. We have provided a formula to assist clinicians in objectively determining if ON hypoplasia is present.
authors.affiliation: Department of Ophthalmology, Division of Pediatric Ophthalmology and Strabismus, Emory University School of Medicine, Emory Eye Center, Atlanta, Georgia. Electronic address: phoebe.lenhart@emory.edu.
authors.forename: Phoebe D
authors.initials: PD
authors.lastname: Lenhart
authors.affiliation: Department of Radiology, Division of Neuroradiology, Emory University School of Medicine, Atlanta, Georgia.
authors.forename: Nilesh K
authors.initials: NK
authors.lastname: Desai
authors.affiliation: Department of Ophthalmology, Division of Neuro-Ophthalmology, Emory University School of Medicine, Emory Eye Center, Atlanta, Georgia; Department of Epidemiology, Rollins School of Public Health and Laney Graduate School, Emory University, Atlanta, Georgia.
authors.forename: Beau B
authors.initials: BB
authors.lastname: Bruce
authors.affiliation: Department of Ophthalmology, Division of Pediatric Ophthalmology and Strabismus, Emory University School of Medicine, Emory Eye Center, Atlanta, Georgia.
authors.forename: Amy K
authors.initials: AK
authors.lastname: Hutchinson
authors.affiliation: Department of Ophthalmology, Division of Pediatric Ophthalmology and Strabismus, Emory University School of Medicine, Emory Eye Center, Atlanta, Georgia.
authors.forename: Scott R
authors.initials: SR
authors.lastname: Lambert
mesh_terms: D000293:Adolescent; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008279:Magnetic Resonance Imaging; D008297:Male; D009898:Optic Disk / Q000473:pathology; D009900:Optic Nerve / Q000473:pathology; D009901:Optic Nerve Diseases / Q000151:congenital* / Q000175:diagnosis; D012189:Retrospective Studies