title: A hierarchical cluster analysis of normal-tension glaucoma using spectral-domain optical coherence tomography parameters.
abstract: OBJECTIVE
  Normal-tension glaucoma (NTG) is a heterogenous disease, and there is still controversy about subclassifications of this disorder. On the basis of spectral-domain optical coherence tomography (SD-OCT), we subdivided NTG with hierarchical cluster analysis using optic nerve head (ONH) parameters and retinal nerve fiber layer (RNFL) thicknesses.
  
  
  METHODS
  A total of 200 eyes of 200 NTG patients between March 2011 and June 2012 underwent SD-OCT scans to measure ONH parameters and RNFL thicknesses. We classified NTG into homogenous subgroups based on these variables using a hierarchical cluster analysis, and compared clusters to evaluate diverse NTG characteristics.
  
  
  RESULTS
  Three clusters were found after hierarchical cluster analysis. Cluster 1 (62 eyes) had the thickest RNFL and widest rim area, and showed early glaucoma features. Cluster 2 (60 eyes) was characterized by the largest cup/disc ratio and cup volume, and showed advanced glaucomatous damage. Cluster 3 (78 eyes) had small disc areas in SD-OCT and were comprised of patients with significantly younger age, longer axial length, and greater myopia than the other 2 groups.
  
  
  CONCLUSIONS
  A hierarchical cluster analysis of SD-OCT scans divided NTG patients into 3 groups based upon ONH parameters and RNFL thicknesses. It is anticipated that the small disc area group comprised of younger and more myopic patients may show unique features unlike the other 2 groups.
authors.affiliation: Departments of *Ophthalmology, Severance Hospital, Institute of Vision Research †Research Affairs, Biostatistics Collaboration Unit, Yonsei University College of Medicine ‡Departments of Ophthalmology, Asan Medical Center, College of Medicine, University of Ulsan, Seoul, Korea.
authors.forename: Hyoung Won
authors.initials: HW
authors.lastname: Bae
authors.forename: Yongwoo
authors.initials: Y
authors.lastname: Ji
authors.forename: Hye Sun
authors.initials: HS
authors.lastname: Lee
authors.forename: Naeun
authors.initials: N
authors.lastname: Lee
authors.forename: Samin
authors.initials: S
authors.lastname: Hong
authors.forename: Gong Je
authors.initials: GJ
authors.lastname: Seong
authors.forename: Kyung Rim
authors.initials: KR
authors.lastname: Sung
authors.forename: Chan Yun
authors.initials: CY
authors.lastname: Kim
mesh_terms: D000328:Adult; D016000:Cluster Analysis; D005260:Female; D006801:Humans; D007429:Intraocular Pressure; D057066:Low Tension Glaucoma / Q000145:classification* / Q000175:diagnosis; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers / Q000473:pathology*; D009898:Optic Disk / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000145:classification* / Q000175:diagnosis; D012165:Retinal Ganglion Cells / Q000473:pathology*; D041623:Tomography, Optical Coherence / Q000379:methods