Sonographic Assessment of Optic Disc Cupping and its Diagnostic Performance in Glaucoma

The purpose of this study was to assess the optic cup diameter sonographically in glaucoma patients and in the normal population and correlate it with their photographic parameters to propose a cut-off value as a predictive index of glaucoma.

A total of 95/50 primary open-angle glaucoma and 87/44 control patients with clear media underwent visual field assessment, fundus photography, and B-scan ultrasound. Photographic vertical cup diameter (PVCD) of cases and controls were recorded after magnification correction using the Bengtsson formula. Sonographic vertical cup diameter (SVCD) was measured in the vertical transverse position.

The mean SVCD was 1.13±0.23 mm in glaucoma and 0.72±0.25 mm in controls (P=0.001). The mean PVCD was 1.024±0.199 mm in glaucoma and 0.636±0.217 mm in controls (P=0.001). A strong correlation between PVCD and SVCD in both groups was found (correlation coefficient r=0.857; P=0.001; glaucoma and r=0.795; P=0.001; control). SVCD had a positive correlation with vertical cup disc ratio (r=0.675; P=0.001 in glaucoma patients) and (r=0.797; P=0.001 in controls) cup area (r=0.798; P=0.001; glaucoma) and (r=0.727, P=0.001; control) a negative correlation with vertical neuroretinal rim diameter (r=-0.5187; P=0.000; glaucoma patients) and (r=-0.699; P=0.001; controls). No correlation of SVCD was found with severity of field grade changes. The receiving operative curve analysis was performed, and Youden's optimal cut-off method was used to find a cut-off value for SVCD, which came out to be 1.06, with 65.3% (95% confidence interval, 54.8-74.7) sensitivity and 94.3% (95% confidence interval, 87.1-97.1) specificity.

The sonographic evaluation of the optic cup is a reliable noninvasive procedure and a potentially useful tool in the assessment of nonviewable suspected glaucomatous cups.