Agreement Between Stereophotographic and Confocal Scanning Laser Ophthalmoscopy Measurements of Cup/Disc Ratio: Effect on a Predictive Model for Glaucoma Development

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Abstract
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. Cross-sectional study. 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 stereophotographs. 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. 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 (rho=0.954; P<0.001). The 95% limits of agreement were -4.57% to 4.65%. 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.