Purpose: To determine the repeatability and agreement between a digital camera (monoscopic and stereoscopic images) and the Heidelberg Retina Tomograph (HRT; Heidelberg Engineering, Heidelberg, Germany) in determining cup-to-disc ratio. A secondary purpose was to determine the monoscopic and stereoscopic thresholds that maximize specificity and sensitivity when compared with the HRT.

Methods: Community living participants aged between 70 and 79 years had their optic discs imaged with a digital nonmydriatic retinal camera (NMRC) and the HRT. Intraclass correlation coefficients (ICCs) and 95% tolerance limits of change were used to determine repeatability characteristics of the instruments. The agreement between the HRT- and NMRC-derived area cup-to-disc ratios was assessed using weighted kappa statistics and receiver operator characteristic (ROC) curves.

Results: The agreements between the monoscopic and stereoscopic images and HRT were assessed for 1238 and 1173 eyes, respectively. The reliability measures for both NMRC techniques and HRT were almost perfect (ICC = 0.84-0.99) with narrow tolerance limits of change (9.2%-18.4%) and very small systemic biases (P < 0.05). The agreement between the HRT and both NMRC techniques was substantial, with a weighted kappa = 0.83. The HRT gave a marginally larger area cup-to-disc ratio than the monoscopic and stereoscopic images by 0.008 and 0.006, respectively (P < 0.001). The areas under the ROC curves for both NMRC techniques were 0.98, indicating excellent discriminating characteristics (P < 0.001). An area cup-to-disc ratio cutoff of > or =0.5 for the monoscopic and stereoscopic NMRC was highly specific (94.1% and 91.6%) and sensitive (87.5% and 97.2%, respectively) in determining an HRT-derived area cup-to-disc ratio >0.6.

Conclusions: The monoscopic and stereoscopic digital images showed excellent repeatability and demonstrated substantial agreement with the HRT. The results indicate that the digital NMRC could be a reliable and useful instrument for assessing area cup-to-disc ratio and screening for glaucoma-suspect eyes in the community.