Advanced imaging for glaucoma study: design, baseline characteristics, and inter-site comparison.

PURPOSE: 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.
DESIGN: 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.