Impact of optical coherence tomography scan direction on the reliability of peripapillary retinal nerve fiber layer measurements

Abstract

Purpose To evaluate the intradevice repeatability and agreement for peripapillary retinal nerve fiber layer (pRNFL) measurements in healthy eyes with two different scan directions and two different number of B scans. Methods pRNFL was measured with a spectral domain optical coherence tomography on 54 healthy participants. Three-dimensional optic disc scans (6 mm x 6 mm) were performed on the right eye of the participants. Two repeated scans were performed in four different settings: H1: Horizontal scan with 512 A-scans x 96 B-scans; H2: Horizontal scan with 512 A-scans x 128 B-scans; V1: Vertical scan with 512 A-scans x 96 B-scans; V2: Vertical scan with 512 A-scans x 128 B-scans. The pRNFL thickness was evaluated in twelve clock-hour sector in a circle of 3.45 mm diameter centred at the optic disc. Repeatability and agreement were assessed with within subject standard deviation (Sw) and Bland-Altman test respectively. Results The repeatability of pRNFL measurements varied depending on the scan direction and sectors. The repeatability for the horizontal sectors were better with H1 and H2, with sector 9 having the best Sw (< 3 μm). The repeatability for the vertical sectors were better with V1 and V2 with sector 5 and 9 having the best Sw (< 4 μm). The repeatability with vertical scan was more symmetric among the sectors than with horizontal scans. The repeatability metrics of the sectors did not vary much between H1 and H2 (difference < 2 μm) and between V1 and V2 (difference < 3.2 μm). Comparing horizontal and vertical scans, the vertical sectors had larger limits of agreement of about 45 μm. Conclusion The reliability of the pRNFL thickness measurements is dependent on the direction of the scan and independent on the numbers of B-scans. Vertical scans for pRNFL gives more homogeneous repeatability across the different sectors.

Agreement and precision of wide and cube scan measurements between swept-source and spectral-domain OCT in normal and glaucoma eyes

“…By contrast, the Wide scan and Cube scan in the current study are closer in scan density. It has also been reported previously that the scan direction affects precision, where horizontal scans have better repeatability than vertical scans 21 . The Wide scan in the prior study employed vertical B-scans, while the Optic Disc and Macular Cube scans were captured horizontally and vertically, respectively 15 , thereby potentially contributing to the varied repeatability between the Wide and Cube scans.…”

Precision and Agreement of Individual and Simultaneous Macular and Optic Disc Volumetric Measurements With Spectral Domain Optical Coherence Tomography

“…In all other sectors, the repeatability of the individual scan was better than combined scan. It has been reported previously that the scan direction affects the precision of the pRNFL measurements ( 12 ), where the horizontal sectors had better repeatability with horizontal scanning, whereas with the vertical scanning the repeatability was more homogeneous. In the present study, the combined scan, which had vertical B-scans, did not have a homogeneous repeatability among the sectors.…”

“…Clinical available OCTs have different scanning protocols for the macular and optic disc volumetric measurements. The built-in automated segmentation algorithm provides reliable volumetric measures of different retinal layers (9)(10)(11)(12)(13).…”

Agreement and Precision of Wide and Cube Scan Measurements between Swept-source and Spectral-domain OCT in Normal and Glaucoma Eyes

“…It has also been reported previously that the scan direction affects precision, where horizontal scans have better repeatability than vertical scans. 21 The Wide scan in the prior study employed vertical B-scans, while the Optic Disc and Macular Cube scans were captured horizontally and vertically, respectively, 15 thereby potentially contributing to the varied repeatability between the Wide and Cube scans. With SS-OCT (DRI-OCT-1 Atlantis, Topcon), another study 8 , found comparably good repeatability of macular GCIPL and macular GCC thickness values from the Wide scan and Cube scans in healthy and glaucoma eyes; the current results are consistent with these earlier ones.…”