title: A comparison of cup-to-disc ratio evaluation in normal subjects using stereo biomicroscopy and digital imaging of the optic nerve head.
abstract: The cup-to-disc (CD) ratio evaluated using stereoscopic biomicroscopy was compared with that evaluated by viewing a non-stereo digital image of the optic nerve head. Twenty normal subjects (mean age 26 +/- 4 years) were evaluated by two observers. The average CD ratio was 0.29 with a range of 0-0.80. The intra-class correlations between the observers ranged from 0.82 to 0.96, when comparing horizontal and vertical CD ratios for both evaluation techniques. The mean CD ratio was significantly smaller when viewing the digital image (0.25 +/- 0.01) compared with stereoscopic observation (0.33 +/- 0.03, p < 0.0001). Although the mean differences between the two techniques were small, the percentage of CD ratios that differed by >or=0.2 were between 5 and 25% of evaluations. Caution should be exercised when using stereoscopic and non-stereo digital evaluations of CD ratio interchangeably to assess longitudinal progression in a multi-clinician setting.
authors.affiliation: School of Optometry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1. hrynchal@uwaterloo.ca
authors.forename: Patricia
authors.initials: P
authors.lastname: Hrynchak
authors.forename: Natalie
authors.initials: N
authors.lastname: Hutchings
authors.forename: Deborah
authors.initials: D
authors.lastname: Jones
authors.forename: Trefford
authors.initials: T
authors.lastname: Simpson
mesh_terms: D000328:Adult; D005654:Fundus Oculi; D005901:Glaucoma / Q000175:diagnosis; D006801:Humans; D007091:Image Processing, Computer-Assisted; D015588:Observer Variation; D009898:Optic Disk / Q000033:anatomy & histology*; D010780:Photogrammetry; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted