Agreement between Slit Lamp Examination and Optical Coherence Tomography in Estimating Cup-Disc Ratios

Abstract

To compare optical coherence tomography (OCT) cup-disc ratio measurements with those estimated by two independent examiners using the slit lamp in an evaluation of the optic nerve head (ONH). In 47 eyes each of 47 patients with glaucoma and 47 healthy subjects, the ONH was examined using the slit lamp with a 78 D lens. Two examiners subjectively determined the cup-disc area ratio (A-CDR), the horizontal cup-disc ratio (H-CDR), and the vertical cup-disc ratio (V-CDR). These measurements were compared to objective OCT readings obtained by a third examiner blind to the slit lamp results. For the three variables determined, correlation indices between the OCT readings and the two sets of slit lamp measurements were significantly higher for the glaucoma group than the control group. In the patients with glaucoma, the OCT tended to underestimate A-CDR and overestimate H-CDR. For both these variables, Bland-Altmann analysis revealed significant differences between the two methods that persisted across the whole range of CDRs examined. In contrast, differences in V-CDR varied with disc size. The OCT is a diagnostic tool that provides a complete automatic evaluation of the ONH. However, its measurements vary significantly from those obtained in subjective evaluations performed by experienced ophthalmologists.