title: Comparative study of retinal nerve fiber layer measurement by StratusOCT and GDx VCC, I: correlation analysis in glaucoma.
abstract: OBJECTIVE
  To evaluate the average and regional correlations of retinal nerve fiber layer (RNFL) thickness measured by StratusOCT (optical coherence tomography; Carl Zeiss Meditec, Inc., Dublin, CA) and GDx VCC (Laser Diagnostic Technologies, Inc., San Diego, CA).
  
  
  METHODS
  Eighty-nine subjects-27 normal, 21 with suspected glaucoma, and 41 with glaucoma-were included in this cross-sectional study. The total average and the mean 12-clock-hour RNFL thickness were measured with the StratusOCT and GDx VCC. The discriminating powers of the two techniques for detection of suspected glaucoma and glaucoma were compared by the area under the receiver operating characteristic curves (AUC). Correspondence between StratusOCT and GDx VCC RNFL measurements in each clock hour was examined with linear regression analysis.
  
  
  RESULTS
  The average RNFL thickness in the normal group was measured at 101.38 +/- 7.73 and 55.26 +/- 4.32 mum by StratusOCT and GDx VCC, respectively. Both nerve fiber analyzers demonstrated a double-hump pattern in the RNFL profiles with maximum RNFL thickness located at the inferotemporal and superotemporal clock hours by the StratusOCT and the superior and inferior clock hours by the GDx VCC. Significant differences were found in the total average and the individual clock-hour RNFL thickness between StratusOCT and GDx VCC RNFL measurements in both the normal and the suspected glaucoma/glaucoma groups. The GDx VCC superior RNFL measurement demonstrated the largest AUC (0.909) for detection of suspected glaucoma and glaucoma, whereas the largest AUC (0.901) in StratusOCT was found over the inferotemporal clock hour. The total average RNFL thickness measured with StratusOCT and GDx VCC correlated highly with each other (r = 0.852). When the respective clock-hour RNFL measurements were compared, the correlation coefficient varied with the position around the optic nerve head, with the highest correlation found over the superior and inferior clock hours (11, 12, 1, 6, and 7 o'clock; all with r > 0.700) and the lowest located at the temporal clock hour (9 o'clock; r = 0.277).
  
  
  CONCLUSIONS
  Despite the substantial differences in the values of RNFL thickness, significant correlations were observed between StratusOCT and GDx VCC RNFL measurements. The variations of the correlation coefficient around the optic nerve head suggested that GDx VCC RNFL measurement does not have a fixed relationship with that of StratusOCT and the use of site-specific RNFL birefringences may improve the estimation of RNFL thickness by the GDx VCC. Nevertheless, the GDx VCC was found to be as effective as the StratusOCT in detecting the loss of RNFL in glaucoma.
authors.affiliation: Department of Ophthalmology, Caritas Medical Centre, 111 Wing Hong Street, Sham Shui Po, Hong Kong, People's Republic of China. tlims00@hotmail.com
authors.forename: Christopher Kai-shun
authors.initials: CK
authors.lastname: Leung
authors.forename: Wai-man
authors.initials: WM
authors.lastname: Chan
authors.forename: Kelvin Kam-Long
authors.initials: KK
authors.lastname: Chong
authors.forename: Wing-ho
authors.initials: WH
authors.lastname: Yung
authors.forename: Kai-tat
authors.initials: KT
authors.lastname: Tang
authors.forename: Jackson
authors.initials: J
authors.lastname: Woo
authors.forename: Woon-ming
authors.initials: WM
authors.lastname: Chan
authors.forename: Kwok-kay
authors.initials: KK
authors.lastname: Tse
mesh_terms: D001718:Birefringence; D003430:Cross-Sectional Studies; D003941:Diagnostic Techniques, Ophthalmological; D005901:Glaucoma / Q000175:diagnosis*; D006801:Humans; D007429:Intraocular Pressure; D008875:Middle Aged; D009412:Nerve Fibers / Q000473:pathology*; D009798:Ocular Hypertension / Q000175:diagnosis; D009898:Optic Disk / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000175:diagnosis*; D012372:ROC Curve; D012165:Retinal Ganglion Cells / Q000473:pathology*; D013223:Statistics as Topic; D041623:Tomography, Optical Coherence / Q000379:methods