Inter-visit test-retest variability of OCT in Glaucoma

Purpose To determine the inter-visit test-retest variability (TRV) of a spectral domain optical coherence tomograph, the Topcon 3D OCT-2000, in the measurement of optic nerve head topography, peripapillary retinal nerve fiber layer (pRNFL), and macular ganglion cell complex (GCC) parameters in glaucoma patients. We also examine whether TRV with this instrument varies with the extent of glaucomatous damage. Methods Twenty-four subjects with varying degrees of glaucoma severity provided 41 eyes with usable results for the study. 3D Disc Retinal Nerve Fiber Layer Analysis and Macula V (GCC) scans were repeated 1 week apart, at the same time of day, to determine the inter-visit TRV. TRV was determined using Bland-Altman limits of agreement (LoA) and the resulting coefficients of repeatability (CR). Results The overall horizontal and vertical cup/disc ratio CRs were 0.05 and 0.07, respectively. The GCC CR was 2.9 μm. In contrast, average pRNFL TRV expanded with increasing damage, with the LoA being well fitted by ±(34.67 - 0.294(d)), where d is the pRNFL thickness. A more complex model, with constant LoA of ±5.61 μm at d >82 μm, and linearly expanding TRV below that, achieved marginal significance (P <.06). Conclusions The repeatability of GCC measurements with this instrument was excellent. The determination of statistically significant change in average pRNFL should take into account average pRNFL thickness.