title: Differences between proximal versus distal intraorbital optic nerve diffusion tensor magnetic resonance imaging properties in glaucoma patients.
abstract: OBJECTIVE
  To analyze in vivo the diffusion tensor magnetic resonance imaging (DT-MRI) properties of the intraorbital optic nerve at two different levels: Proximal to the optic nerve head (ONH) and distal to the ONH at the level of the orbital apex in glaucoma patients.
  
  
  METHODS
  Twenty-four patients with primary open-angle glaucoma were examined. The categorization into early and severe glaucoma was performed by Hodapp's classification. Fifteen healthy individuals served as controls. DT-MRI was performed with a 3T-MR unit.
  
  
  RESULTS
  At early stage mean diffusivity (MD) values were higher at the proximal site with respect to the distal site. On the contrary, a decrease in fractional anisotropy (FA) was observed only relative to patient stage, independent of optic nerve site. Moreover, at early disease stage an increase in overall diffusivities, was evident at the proximal site, whereas at the distal site a decrease of the largest diffusivity and an increase in both the intermediate and smallest diffusivities were observed. FA and MD measured at the proximal site, had, respectively, the highest sensitivity and specificity in discriminating between healthy and glaucomatous eyes.
  
  
  CONCLUSIONS
  Our study represents the first attempt to evaluate in vivo fiber integrity changes along the optic nerve with DT-MRI. Optic nerve degeneration appears to be a process that affects differently the proximal and the distal segments of the optic nerve. The complementary high sensitivity of FA with the high specificity of MD at the proximal site may provide reliable indexes for the identification of glaucomatous patients at early stages.
authors.affiliation: Department of Diagnostic Imaging, Molecular Imaging, Interventional Radiology and Radiotherapy, University of Rome, Rome, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Bolacchi
authors.forename: Francesco Giuseppe
authors.initials: FG
authors.lastname: Garaci
authors.forename: Alessio
authors.initials: A
authors.lastname: Martucci
authors.forename: Alessandro
authors.initials: A
authors.lastname: Meschini
authors.forename: Maria
authors.initials: M
authors.lastname: Fornari
authors.forename: Simone
authors.initials: S
authors.lastname: Marziali
authors.forename: Raffaele
authors.initials: R
authors.lastname: Mancino
authors.forename: Ettore
authors.initials: E
authors.lastname: Squillaci
authors.forename: Roberto
authors.initials: R
authors.lastname: Floris
authors.forename: Luciano
authors.initials: L
authors.lastname: Cerulli
authors.forename: Giovanni
authors.initials: G
authors.lastname: Simonetti
authors.forename: Carlo
authors.initials: C
authors.lastname: Nucci
mesh_terms: D000368:Aged; D056324:Diffusion Tensor Imaging / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D005902:Glaucoma, Open-Angle / Q000175:diagnosis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009900:Optic Nerve / Q000473:pathology*; D011446:Prospective Studies; D012372:ROC Curve; D015203:Reproducibility of Results; D012720:Severity of Illness Index