Monocular vs. stereoscopic measurement of cup-to-disc ratios.

Stereoscopic viewing of the optic nerve head and cup has been reported to provide more reliable cup-to-disc (C/D) ratio estimates. We investigated the variability in C/D ratio estimates among three experienced optometric clinicians using conventional direct ophthalmoscopy and indirect biomicroscopy with the Volk 90 D lens. The pupils of 21 subjects were dilated and the discs assessed randomly by each examiner for the determination of the C/D ratio. Analysis of variance indicates that the two methods are not significantly different from each other when comparing interexaminer reliability. However, for a particular examiner, one method may be more effective than the other.