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

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.

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.

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.

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.