Comparison of optic nerve head assessment with a digital stereoscopic camera (discam), scanning laser ophthalmoscopy, and stereophotography

Abstract

Purpose: To compare computer-assisted planimetry using the Discam system (Marcher Enterprises Ltd., Hereford, UK), confocal scanning laser ophthalmoscopy (CSLO), and stereoscopic disc photography with respect to optic nerve head (ONH) measurements and glaucoma status.

Design: Comparative, observational case series and interobserver variability study.

Methods: Three hundred eighty-six eyes of 233 consecutive subjects were imaged with the Discam, and a subset underwent ONH evaluation with CSLO (n = 297), stereoscopic photography (n = 233), or both. Subjects were classified into normal, glaucoma suspect, and glaucoma groups based on clinical findings of slit-lamp disc examination and visual field testing. Agreement of cup-to-disc ratio measurements among the three technologies was assessed by the intraclass correlation coefficient (ICC) and areas under the receiver operator characteristic (AROC) curves.

Main outcome measures: Cup-to-disc ratio as measured by Discam, CSLO, and stereography.

Results: Intraclass correlation coefficients calculated using the two-way random effects model for comparing Discam, CSLO, and stereography among cup-to-disc area ratio, vertical cup-to-disc ratio, and horizontal cup-to-disc ratio were 0.46 to 0.53. The ICC was higher for eyes with larger optic discs (0.51) than those with smaller ones (0.32). The ICC calculated using the fixed effects model for the Discam and CSLO comparison was 0.72. Areas under the receiver operator characteristic curves were 0.67 to 0.80 among the three technologies comparing normal with glaucomatous eyes. In general, there was no statistically significant difference between techniques with respect to sensitivity and specificity of glaucoma detection.

Conclusions: There is good agreement between ONH measurements obtained by Discam, CSLO, and stereography; however, the results are not interchangeable. Similar AROC curve values among all three techniques imply that the Discam, CSLO, and stereography perform equally for the determination of glaucoma status.

Figure 1

Scatter plot showing difference in cup-to-disc area ratio (ACDR) measured by the Heidelberg Retina Tomograph (HRT) and Discam against the average ACDR of the two measurements. Dashed lines represent mean difference and 95% limits of agreement.

Figure 2

Scatter plot showing difference in vertical cup-to-disc ratio (VCDR) measured by stereoscopic disc photography and Discam against the average VCDR of the two measurements. Dashed lines represent mean difference and 95% limits of agreement.

Figure 3

Scatter plot showing difference in horizontal cup-to-disc ratio (HCDR) measured by stereoscopic disc photography and Discam against the average HCDR of the two measurements. Dashed lines represent mean difference and 95% limits of agreement.

Figure 4

Receiver operator characteristic (ROC) curve for cup-to-disc area ratio (ACDR) measured by Discam (continuous line) and the Heidelberg Retina Tomograph (HRT) for distinguishing between glaucoma and normal subjects; areas under the ROC curves (AROCs) are 0.70 and 0.67, respectively. These curves are shown as examples of ROC curves summarized by AROCs in Tables 5 and 6.