title: Advanced imaging for glaucoma study: design, baseline characteristics, and inter-site comparison.
abstract: OBJECTIVE
  To report the baseline characteristics of the participants in the Advanced Imaging for Glaucoma Study. To compare the participating sites for variations among subjects and the performance of imaging instruments.
  
  
  METHODS
  Multicenter longitudinal observational cohort study.
  
  
  METHODS
  A total of 788 participants (1329 eyes) were enrolled from 3 academic referral centers. There were 145 participants (289 eyes) in the normal group, 394 participants (663 eyes) in the glaucoma suspect/preperimetric glaucoma group, and 249 participants (377 eyes) in the perimetric glaucoma group. Participants underwent a full clinical examination, standard automated perimetry, and imaging with time-domain and Fourier-domain optical coherence tomography (OCT), scanning laser polarimetry, and confocal scanning laser ophthalmoscopy. The baseline average, population standard deviation, and repeatability of imaging-derived anatomic variables were reported for each technology and center.
  
  
  RESULTS
  Compared to the normal participants, glaucoma suspect/preperimetric glaucoma and perimetric glaucoma groups had significantly reduced anatomic measurements. Repeatability of nerve fiber layer thickness was best for Fourier-domain OCT (overall coefficient of variation <2%), followed by time-domain OCT (coefficient of variation 2%-2.9%), scanning laser polarimetry (coefficient of variation 2.6%-4.5%), and confocal scanning laser ophthalmoscopy rim area (coefficient of variation 4.2%-7.6%). A mixed-effects model showed that the differences between sites was less than 25 percent of the variation within groups and less than the differences between the normal and glaucoma suspect/preperimetric glaucoma group.
  
  
  CONCLUSIONS
  Site-to-site variation was smaller than both the variation within groups and the changes attributable to glaucoma. Therefore pooling of participants between sites is appropriate.
authors.affiliation: Department of Ophthalmology, University of Southern California, Los Angeles, California.
authors.forename: Phuc V
authors.initials: PV
authors.lastname: Le
authors.affiliation: Casey Eye Institute, Oregon Health & Science University, Portland, Oregon.
authors.forename: Xinbo
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Doheny Eye Institute, University of Southern California, Los Angeles, California.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Francis
authors.affiliation: Department of Ophthalmology, University of Southern California, Los Angeles, California.
authors.forename: Rohit
authors.initials: R
authors.lastname: Varma
authors.affiliation: Bascom Palmer Eye Institute, University of Miami, Miami, Florida.
authors.forename: David S
authors.initials: DS
authors.lastname: Greenfield
authors.affiliation: Eye and Ear Institute, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania.
authors.forename: Joel S
authors.initials: JS
authors.lastname: Schuman
authors.affiliation: Eye and Ear Institute, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania.
authors.forename: Nils
authors.initials: N
authors.lastname: Loewen
authors.affiliation: Casey Eye Institute, Oregon Health & Science University, Portland, Oregon. Electronic address: davidhuang@alum.mit.edu.
authors.forename: David
authors.initials: D
authors.lastname: Huang
mesh_terms: D000328:Adult; D000368:Aged; D003952:Diagnostic Imaging / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D005583:Fourier Analysis; D005901:Glaucoma / Q000175:diagnosis*; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers / Q000473:pathology*; D009798:Ocular Hypertension / Q000175:diagnosis; D009887:Ophthalmoscopy; D009898:Optic Disk / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000175:diagnosis*; D011237:Predictive Value of Tests; D011446:Prospective Studies; D015203:Reproducibility of Results; D012107:Research Design; D012165:Retinal Ganglion Cells / Q000473:pathology*; D057109:Scanning Laser Polarimetry; D041623:Tomography, Optical Coherence; D058609:Visual Field Tests