title: Retrobulbar optic nerve diameter measured by high-speed magnetic resonance imaging as a biomarker for axonal loss in glaucomatous optic atrophy.
abstract: OBJECTIVE
  To assess a novel magnetic resonance imaging (MRI) protocol for quantifying the optic nerve diameter (OND) as a measure of axonal loss in the optic nerve.
  
  
  METHODS
  Included in the study was one eye each from 47 subjects, of whom 9 had no eye disease, 16 had preperimetric glaucoma, 11 had a glaucomatous mean visual field defect of <10 dB and 11 of >10 dB. Each subject underwent automated perimetry, scanning laser polarimetry, optic coherence tomography, scanning laser tomography, and ultrafast high-resolution MRI at 3 T. OND was determined 5, 10, and 15 mm behind the eye with a half Fourier-acquired single-shot turbo spin-echo (HASTE)-sequence requiring 1.5 seconds of data acquisition time per slice and providing a spatial resolution of 0.11 mm. A multiple linear regression model was applied to determine correlations (r) among the different techniques.
  
  
  RESULTS
  The correlation (r) was <0.37 for OND measurements taken 5 mm behind the eye. At 10 mm behind the eye, r increased to 0.57 and was statistically significant in four out six instances. In the orbital apex 15 mm behind the eye, r reached a maximum of 0.80 and was statistically significant in all instances. OND correlated best with the retinal nerve fiber layer thickness measured by optic coherence tomography.
  
  
  CONCLUSIONS
  Retina- or optic nerve head-related surrogate markers for axonal content correlated closely with the OND, although only when it was measured in the orbital apex. High-resolution MRI using an ultrafast HASTE-sequence at 3 T proved useful for OND quantification and may be a valuable asset in future neuroprotection trials.
authors.affiliation: Department of Ophthalmology, University Hospital Freiburg, Freiburg, Germany.
authors.forename: Wolf A
authors.initials: WA
authors.lastname: Lagrèze
authors.forename: Mirjam
authors.initials: M
authors.lastname: Gaggl
authors.forename: Matthias
authors.initials: M
authors.lastname: Weigel
authors.forename: Jürgen
authors.initials: J
authors.lastname: Schulte-Mönting
authors.forename: Anima
authors.initials: A
authors.lastname: Bühler
authors.forename: Michael
authors.initials: M
authors.lastname: Bach
authors.forename: Robin D
authors.initials: RD
authors.lastname: Munk
authors.forename: Thorsten A
authors.initials: TA
authors.lastname: Bley
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001369:Axons / Q000473:pathology*; D003430:Cross-Sectional Studies; D005583:Fourier Analysis; D005902:Glaucoma, Open-Angle / Q000175:diagnosis*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D009896:Optic Atrophy / Q000175:diagnosis*; D009898:Optic Disk / Q000473:pathology*; D012165:Retinal Ganglion Cells / Q000473:pathology*; D041623:Tomography, Optical Coherence; D014786:Vision Disorders / Q000175:diagnosis; D058609:Visual Field Tests; D014794:Visual Fields