PURPOSE: To compare the level of agreement between subjective and objective methods in estimating horizontal and vertical cup-to-disc ratios (HCDR and VCDR, respectively) to determine if objective techniques may be used as surrogates for subjective cup-to-disc (CDR) estimation. METHODS: Fifty-one glaucoma patients and 49 control subjects underwent full ophthalmic examination, stereoscopic optic nerve head photographs (ONHPs), confocal scanning laser ophthalmoscopy (Heidelberg Retina Tomography II [HRT II]), and optical coherence tomography (Stratus OCT). The intraclass correlation coefficient (ICC) and Bland Altman plots were used to assess the agreement across the three methods. Repeated measures analysis of variance (ANOVA), Tukey adjustment, and pairwise P values were used to compare the HCDR and VCDR estimates between three clinicians who reviewed photos, Stratus OCT, and HRT II. RESULTS: For the clinicians, the agreement in subjectively assessed HCDR and VCDR was substantial (ICC=0.84 and 0.85, respectively), and for all three methods, overall agreement was good (ICC=0.75 and 0.77 for the HCDR and VCDR, respectively). Stratus OCT provided the largest overall mean±SD HCDR (0.68±0.14) and VCDR (0.62±0.13). The smallest overall mean±SD HCDR was provided by ONHP (0.32±0.16), and the smallest overall mean±SD VCDR was provided by HRT II (0.26±0.20). Repeated measures ANOVA test demonstrated significant differences across the three methods for glaucomatous (P=0.0017 and 0.0016, HCDR and VCDR, respectively) and normal (P=0.0001 for both HCDR and VCDR) eyes. Tukey adjustment demonstrated specific statistical differences between pairs of methods. CONCLUSIONS: Although the overall agreement between various methods was good, the mean estimates were statistically different. Additional studies are needed to evaluate the sources of variability, their level of significance, and longitudinal agreement between various methods of the CDR estimation. Copyright © 2006 by Lippincott Williams & Wilkins.