title: Long-term variability of GDx VCC retinal nerve fiber layer thickness measurements.
abstract: OBJECTIVE
  To evaluate the long-term variability of GDx VCC retinal nerve fiber layer (RNFL) thickness measurements.
  
  
  METHODS
  The study enrolled a cohort of glaucoma suspects who did not develop any evidence of visual field damage or change in the appearance of the optic nerve during an average follow-up of 9.1+/-3.2 years. Subjects underwent ocular imaging using the commercially available GDx VCC scanning laser polarimeter. At each visit, each eye was imaged 3 times. Subjects underwent repeated testing with GDx VCC at approximately 12-month intervals during their follow-up. In total, 255 examinations were obtained in 31 eyes of 31 individuals during an average GDx VCC follow-up time of 26.0+/-8.9 months. A random effects analysis of variance model was used to estimate intraclass correlation coefficients and long-term and short-term variability estimates.
  
  
  RESULTS
  Intraclass correlation coefficients ranged from 0.77 to 0.86 for GDx VCC parameters. Short-term variability estimates ranged from 2.45 to 3.89 microm for RNFL thickness parameters, whereas the short-term variability estimate for the parameter Nerve Fiber Indicator was 3.71. Long-term variability was slightly higher than short-term variability for all parameters. For RNFL thickness parameters, long-term variability estimates ranged from 3.21 to 4.97 microm, whereas for the parameter Nerve Fiber Indicator the long-term variability estimate was 4.93.
  
  
  CONCLUSIONS
  RNFL measurements obtained with the GDx VCC were found to be highly reproducible in a long-term test-retest situation, supporting the use of this instrument for longitudinal assessment of the RNFL.
authors: Department of Ophthalmology, Hamilton Glaucoma Center, University of California, San Diego, CA 92093-0946, USA. fmedeiros@eyecenter.ucsd.edu
authors: Felipe A
authors: FA
authors: Medeiros
authors: Rishi
authors: R
authors: Doshi
authors: Linda M
authors: LM
authors: Zangwill
authors: Cristiana
authors: C
authors: Vasile
authors: Robert N
authors: RN
authors: Weinreb
mesh_terms: D001718:Birefringence; D003315:Cornea / Q000502:physiology; D003941:Diagnostic Techniques, Ophthalmological; D005500:Follow-Up Studies; D006801:Humans; D007834:Lasers; D008027:Light; D008875:Middle Aged; D009412:Nerve Fibers / Q000473:pathology*; D009798:Ocular Hypertension / Q000175:diagnosis*; D009901:Optic Nerve Diseases / Q000175:diagnosis*; D011446:Prospective Studies; D015203:Reproducibility of Results; D012165:Retinal Ganglion Cells / Q000473:pathology*