Agreement Between Stereophotographic and Confocal Scanning Laser Ophthalmoscopy Measurements of Cup/Disc Ratio: Effect on a Predictive Model for Glaucoma Development Felipe A. Medeiros, MD, PhD, Linda M. Zangwill, PhD, Christopher Bowd, PhD, Cristiana Vasile, MD, Pamela A. Sample, PhD, and Robert N. Weinreb, MD Objective: To evaluate risk estimates obtained by incorporating confocal scanning laser ophthalmoscopy measurements of cup/ disc (C/D) ratio into a previously described and validated predictive model to estimate the risk of glaucoma development in ocular hypertension. These risk estimates were compared with those obtained by the original model in which vertical C/D ratio was estimated from stereophotographs. Design: Cross-sectional study. Methods: The study included 118 eyes of 59 patients with normal optic discs, normal visual fields, and high intraocular pressure. The original predictive model contained information on 6 baseline factors: age, intraocular pressure, central corneal thickness, vertical C/D ratio, visual field pattern standard deviation, and presence of diabetes. Information regarding these baseline factors was collected for each patient. For the original model, vertical C/D ratio was estimated from stereo- photographs. The Heidelberg Retina Tomograph (HRT) model used an identical model, except that the parameter linear C/D ratio was used to provide C/D ratio estimates. All patients underwent confocal scanning laser ophthalmoscopy imaging HRT II within 6 months of stereophotographs. The agreement between stereophotograph and HRT II risk estimates was evaluated by Bland-Altman plots. Results: The difference between HRT II and stereophotograph estimates of C/D ratio was within 0.2 in 95% of the patients. When incorporated into the predictive model, estimates of risk using the HRT II parameter linear C/D ratio were highly correlated to those obtained using stereophotographs (r = 0.954; P <0.001). The 95% limits of agreement were  4.57% to 4.65%. Conclusions: HRT II and stereophotograph estimates of C/D ratio can be used interchangeably when incorporated into a predictive model to estimate the risk of conversion from ocular hypertension to glaucoma. Key Words: ocular hypertension, risk, confocal scanning laser ophthalmoscopy, glaucoma (J Glaucoma 2007;16:209–214) R ecent results from the Ocular Hypertension Treatment Study (OHTS) have shown that the risk of glaucoma development among ocular hypertensive patients varies according to the prevalence of certain risk factors. 1 It has been suggested that the decision to treat a patient with ocular hypertension (OHT) should, therefore, involve an assessment of risk factors for the development of glaucomatous damage. In a previous study, we developed a predictive model to estimate the 5-year risk of glaucoma conversion based on the results of the OHTS. 2 The model was validated on an independent population of 126 OHT subjects and performed well in discriminating patients with OHT who developed glaucoma from those who did not, also providing reliable predictions of risk. The predictive model incorporates the 6 factors found to be significantly associated with the risk of glaucoma devel- opment in the OHTS: age, baseline intraocular pressure (IOP), corneal thickness, visual field pattern standard deviation (PSD) index, vertical cup/disc (C/D) ratio, and diabetes. Both in the OHTS and in our previous study, estimates of vertical C/D ratio were obtained from stereophotographs of the optic disc reviewed by 2 or more experienced examiners. This could potentially limit the applicability of the predictive model in clinical practice, as there is an evidence indicating that optic disc photographs are not routinely obtained in most clinical settings. 3–5 Further, estimates of C/D ratio from stereo- photographs suffer from the inherent variability owing to the subjective assessment. 6–8 Confocal scanning laser ophthalmoscopy (CSLO) is an imaging technology designed originally to provide Copyright r 2007 by Lippincott Williams & Wilkins Received for publication July 20, 2006; accepted October 30, 2006. From the Hamilton Glaucoma Center, University of California, San Diego, CA. Supported in part by an independent research grant from Pfizer, Inc (FAM) and by National Eye Institute grants EY11008 (LMZ) and EY08208 (PAS). Reprints: Felipe A. Medeiros, MD, PhD, Hamilton Glaucoma Center, University of California, San Diego, 9415 Campus Point Dr., 0946, La Jolla, CA 92093-0946 (e-mail: fmedeiros@eyecenter.ucsd.edu). ORIGINAL STUDY J Glaucoma  Volume 16, Number 2, March 2007 209