Agreement among 3 Optical Imaging Methods for the Assessment of Optic Disc Topography Esther M. Hoffmann, MD, 1 Christopher Bowd, PhD, 1 Felipe A. Medeiros, MD, 1 Catherine Boden, PhD, 1 Franz H. Grus, MD, PhD, 2 Rupert R. Bourne, MD, 1 Linda M. Zangwill, PhD, 1 Robert N. Weinreb, MD 1 Purpose: To assess the agreement of disc topography measurements between the Heidelberg Retina Tomograph (HRT II), Retinal Thickness Analyzer (RTA), and Optical Coherence Tomograph (StratusOCT). Design: Observational cross-sectional study. Participants: Forty-two randomly chosen eyes of 42 subjects. Methods: Each subject underwent HRT II, RTA, and StratusOCT examination. Two experienced examiners drew the contour lines for the HRT II and RTA. Bland and Altman plots were used to evaluate agreement for each topographic parameter among the instruments. The Spearman coefficient of rank correlation was evaluated for each topographic parameter. Main Outcome Measures: Agreement in the measurement of optic disc topography among 3 imaging instruments, as evaluated by regression-based 95% limits of agreement. Results: For optic disc area, the agreement between HRT II–RTA and StratusOCT–RTA revealed the existence of proportional bias, indicated by significant slopes of the regression lines (P = 0.01 and P = 0.02, respectively). The 95% limits of agreement between instruments varied with the actual optic disc size measure- ment. Heidelberg Retina Tomograph disc area measurements tended to be consistently lower than StratusOCT disc area measurements (fixed bias). The Spearman correlation coefficient between the instruments ranged from r = 0.35 (rim area, HRT II–StratusOCT) to r = 0.91 (cup area, HRT II–RTA). Conclusions: Moderate to high correlation was found in measurements of optic disc topography among different instruments. However, the analysis of agreement indicated important discrepancies among instruments. Therefore, these instruments should not be used interchangeably to obtain measurements of the optic disc for glaucoma diagnosis. Ophthalmology 2005;112:2149 –2156 © 2005 by the American Academy of Ophthalmology. Assessment of the optic disc is important for diagnosis and management of glaucoma. 1–4 A number of studies have shown that morphological changes frequently are observ- able before functional loss can be detected using standard achromatic perimetry. 5–9 Several imaging methods are cur- rently employed in clinical practice to obtain quantitative stereometric and volumetric information of the optic disc. 10 –18 Each of these instruments can detect glaucoma with moderate to high sensitivity. 10,11,19 –21 However, al- though these instruments measure similar characteristics of optic disc topography, their measurements may not be interchangeable. The purpose of this study was to compare measurements of optic disc topography obtained using 3 different com- mercially available optical imaging instruments. Materials and Methods This observational cross-sectional study included 48 subjects who were imaged with the Heidelberg Retina Tomograph II (HRT II) (Heidelberg Engineering, Dossenheim, Germany), Retinal Thick- ness Analyzer (RTA) (Talia Technology Ltd., Neve Ilan, Israel), and Optical Coherence Tomograph (StratusOCT, Carl Zeiss Med- itec, Dublin, CA) within 3 months between February and Septem- ber 2004. One randomly selected eye of all subjects was analyzed. All subjects were evaluated at the Hamilton Glaucoma Center, University of California, San Diego as part of the Diagnostic Innovations in Glaucoma Study, a prospective longitudinal study designed to evaluate optic nerve structure and visual function in glaucoma. All patients who met the inclusion criteria described were enrolled in the current study. Patients were selected retro- spectively from our research database. Informed consent was ob- tained from all participants. The University of California, San Diego Human Subjects Committee approved all protocols, and the Originally received: January 20, 2005. Accepted: July 6, 2005. Manuscript no. 2005-67. 1 Hamilton Glaucoma Center, Department of Ophthalmology, University of California, San Diego, La Jolla, California. 2 Department of Ophthalmology, University of Mainz, Mainz, Germany. Research support: Deutsche Forschungsgemeinschaft, Bonn, Germany (grant no.: Ho 3277/1-1 [EMH]), and the National Institutes of Health, Bethesda, Maryland (grant no.: EY 11008 [LMZ]). Financial disclosure: Dr Weinreb receives research support (instruments) from Carl Zeiss Meditec and Heidelberg Engineering. Correspondence to Robert N. Weinreb, MD, Hamilton Glaucoma Center, Department of Ophthalmology, University of California of San Diego, 9500 Gilman Drive, La Jolla, CA, 92093-0946. 2149 © 2005 by the American Academy of Ophthalmology ISSN 0161-6420/05/$–see front matter Published by Elsevier Inc. doi:10.1016/j.ophtha.2005.07.003