Intraday Repeatability of Bruch's Membrane Opening-Based Neuroretinal Rim Measurements

Purpose: To assess possible intraday variability in Bruch's membrane opening-based (BMO) assessment of neuroretinal rim by spectral-domain optical coherence tomography (SD-OCT) of the optic nerve head (ONH) as well as to evaluate its independence from intraindividual IOP changes. Methods: In this noninterventional, prospective cohort study, 51 consecutively enrolled patients with glaucoma or ocular hypertension underwent standardized SD-OCT of the ONH and IOP assessment at two different time points with a time gap of 5 hours on the same day. Random effects models, intraclass correlation coefficients (ICC) and Bland-Altman plots were used to analyze repeatability of BMO minimum rim width (BMO-MRW) and area (BMO-MRA) and peripapillary retinal nerve fiber layer (RNFL) thickness measurements. Results: Mean BMO area was 1.86 ± 0.30 mm2. At baseline, mean BMO-MRW was 206.46 ± 0.86 μm, mean BMO-MRA was 0.89 ± 0.34 mm2, and mean RNFL thickness was 71.61 ± 0.20 μm. Within intraindividual measurements, mean difference was 2.95 μm or 1.76% for BMO-MRW, 0.02 mm2 or 2.68% for BMO-MRA, and 1.18 μm or 1.89% for RNFL thickness. Comparing time points, η2 was 0.001 (P = 0.757) for RNFL thickness, 0.043 (P = 0.01) for BMO-MRA, and 0.07 (P = 0.06) for BMO-MRW. Intraclass correlation coefficients were greater than 0.994, respectively. Variability of morphometric parameters did not correlate to intraindividual IOP fluctuations. Conclusions: Assessment of BMO-MRW by SD-OCT shows high intraday repeatability, which is comparable to the parameter RNFL thickness. Variability seems not to be driven by typical moderate intraday fluctuations of IOP. The two-dimensional parameter BMO-MRA incorporates a fairly higher intraindividual variability.