Correlation between cup-to-disc ratio and cup/retrobulbar optic nerve diameter proportion assessed by high-resolution ultrasound in glaucomatous eyes

Abstract

To investigate the correlation between the measurements of the cup/retrobulbar optic nerve diameter (C/OND) proportion obtained by high-resolution 20-MHz B-mode ultrasound (US) and those of the cup/disc ratio (C/D) obtained by fundus biomicroscopy (BIO) and optical coherence tomography (OCT). Thirty eyes of 15 glaucomatous patients with any C/D proportion were studied. All patients underwent examination of the vertical C/D by BIO with a 78D lens and time-domain OCT analysis, as well as the vertical C/OND proportion using 20-MHz US measurements. All data were analyzed by correlation and agreement tests. The Spearman test showed a strong correlation between C/D results obtained by BIO and the measurements of C/OND (US) (r=0.788, p<0.0001), and with C/D obtained by OCT (r=0.8529, p<0.0001). However, comparison of C/D results obtained with OCT to those obtained by with C/OND (US) showed only a moderate correlation (r=0.6727, p<0.0001). Bland-Altman analysis did not show good agreement between C/D (BIO) and C/OND (US). The results demonstrate that B-mode ultrasound examination with a 20 MHz probe can be a good additional method for the evaluation of the C/D ratio in glaucomatous patients, and may be considered as an alternative gross tool in glaucomatous patients with optic media opacities.