Objective: We assessed agreement between cup/disk ratio measurements obtained by glaucoma expert evaluation of stereoscopic photographs of the optic disk and those obtained with a confocal scanning laser ophthalmoscope.

Methods: Three glaucoma experts estimated vertical and horizontal cup/disk ratios from stereoscopic photographs of 15 normal subjects and 15 patients with glaucoma. These estimates were compared to vertical, horizontal, and area cup/disk ratios measured with a confocal scanning laser ophthalmoscope. Intraobserver and interobserver agreements were also estimated.

Results: Agreement between clinicians and the confocal scanning laser ophthalmoscope varied by clinician. Agreement was moderate to substantial for vertical cup/disk ratio and fair to moderate for horizontal cup/disk ratio; kappas ranged from 0.57 to 0.72 and from 0.21 to 0.55, respectively. The mean confocal scanning laser ophthalmoscope area cup/disk ratio measurements were smaller than each clinician's mean vertical and horizontal cup/disk ratio estimates; differences ranged from 0.10 to 0.24 and from 0.06 to 0.16, respectively. Differences were smaller between clinician estimates and instrument measurements of horizontal and vertical cup/disk ratios of patients with glaucoma than normal subjects.

Conclusions: These results demonstrate good agreement between confocal scanning laser ophthalmoscope measurements and clinician estimates of the vertical cup/disk ratios from stereoscopic photographs, particularly of patients with glaucoma. However, as differences between clinician and instrument estimates of cup/disk ratios were found, new quantitative criteria must be established for characterizing a disk as glaucomatous using confocal scanning laser ophthalmoscopy.