title: Glaucoma severity affects diffusion tensor imaging (DTI) parameters of the optic nerve and optic radiation.
abstract: OBJECTIVE
  To evaluate whether MR diffusion tensor imaging (DTI) of the optic nerve and optic radiation in glaucoma patients provides parameters to discriminate between mild and severe glaucoma and to determine whether DTI derived indices correlate with retinal nerve fibre layer (RNFL) thickness.
  
  
  METHODS
  3-Tesla DTI was performed on 90 subjects (30 normal, 30 mild glaucoma and 30 severe glaucoma subjects) and the FA and MD of the optic nerve and optic radiation were measured. The categorisation into mild and severe glaucoma was done using the Hodapp-Parrish-Anderson (HPA) classification. RNFL thickness was also assessed on all subjects using OCT. Receiver operating characteristic (ROC) analysis and Spearman's correlation coefficient was carried out.
  
  
  RESULTS
  FA and MD values in the optic nerve and optic radiation decreased and increased respectively as the disease progressed. FA at the optic nerve had the highest sensitivity (87%) and specificity (80%). FA values displayed the strongest correlation with RNFL thickness in the optic nerve (r=0.684, p ≤ 0.001) while MD at the optic radiation showed the weakest correlation with RNFL thickness (r=-0.360, p ≤ 0.001).
  
  
  CONCLUSIONS
  The high sensitivity and specificity of DTI-derived FA values in the optic nerve and the strong correlation between DTI-FA and RNFL thickness suggest that these parameters could serve as indicators of disease severity.
authors.affiliation: Department of Biomedical Imaging, University Malaya, Research Imaging Centre, Faculty of Medicine, University Malaya, Malaysia; Medical Imaging Unit, Faculty of Medicine, Universiti Teknologi MARA, Selangor, Malaysia.
authors.forename: S
authors.initials: S
authors.lastname: Sidek
authors.affiliation: Department of Biomedical Imaging, University Malaya, Research Imaging Centre, Faculty of Medicine, University Malaya, Malaysia.
authors.forename: N
authors.initials: N
authors.lastname: Ramli
authors.affiliation: Department of Biomedical Imaging, University Malaya, Research Imaging Centre, Faculty of Medicine, University Malaya, Malaysia. Electronic address: katt_xr2000@yahoo.com.
authors.forename: K
authors.initials: K
authors.lastname: Rahmat
authors.affiliation: Department of Ophthalmology, Faculty of Medicine, University Malaya, Kuala Lumpur, Malaysia.
authors.forename: N M
authors.initials: NM
authors.lastname: Ramli
authors.affiliation: Department of Ophthalmology, Faculty of Medicine, University Malaya, Kuala Lumpur, Malaysia.
authors.forename: F
authors.initials: F
authors.lastname: Abdulrahman
authors.affiliation: Department of Biomedical Imaging, University Malaya, Research Imaging Centre, Faculty of Medicine, University Malaya, Malaysia.
authors.forename: L K
authors.initials: LK
authors.lastname: Tan
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003430:Cross-Sectional Studies; D056324:Diffusion Tensor Imaging / Q000379:methods*; D005260:Female; D005901:Glaucoma / Q000473:pathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009901:Optic Nerve Diseases / Q000473:pathology*; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index
keywords: Degeneration; Diffusion tensor imaging; Glaucoma; MRI; Optic pathway