Comparison of Cup-to-disc Ratio Estimates Using Wide Field Fundus Photography and Optical Coherence Tomography

Purpose: We compared cup-to-disc ratio estimates obtained using wide-field fundus photography and optical coherence tomography (OCT), both of which are widely used for fundus examination.Methods: In total, 130 eyes from 65 patients were included and categorized as 53 right eyes and 53 left eyes from patients with diabetes mellitus, and 12 right eyes and 12 left eyes from patients without diabetes mellitus. Vertical cup-to-disc ratios (VCDRs) were measured using wide-field fundus photography and OCT. Differences in VCDR measurements between the two modalities were analyzed using generalized estimating equations with an exchangeable working correlation structure to account for within-subject correlation between fellow eyes.Results: Mean VCDRs measured using wide-field fundus photography were 0.64 ± 0.17 and 0.61 ± 0.16 for diabetic right and left eyes, respectively, and 0.69 ± 0.14 and 0.64 ± 0.21 for non-diabetic right and left eyes, respectively. Corresponding VCDRs measured using OCT were 0.69 ± 0.12 and 0.67 ± 0.13 for diabetic right and left eyes, respectively, and 0.60 ± 0.24 and 0.68 ± 0.12 for non-diabetic right and left eyes, respectively. OCT significantly overestimated VCDRs in diabetic eyes compared to wide-field fundus photography. In contrast, OCT underestimated VCDRs in non-diabetic right eyes and overestimated VCDRs in non-diabetic left eyes; however, these differences were not statistically significant. Generalized estimating equation analysis demonstrated that diabetes mellitus was a significant factor associated with differences in VCDR measurements between wide-field fundus photography and OCT.Conclusions: VCDRs measured using OCT in patients with diabetes mellitus were greater than those estimated using wide-field fundus photography. These findings emphasize the importance of carefully selecting and interpreting diagnostic, screening, and follow-up modalities for VCDR assessment in patients with diabetes mellitus.