Impact of Scan Tilt on Quantitative Assessments Using Optical Coherence Tomography Angiography

Purpose To investigate the impact of scan tilt on quantitative assessments using swept-source optical coherence tomography angiography (SS-OCTA) in healthy participants. Methods Healthy participants were imaged with a SS-OCTA system (PLEX Elite 9000; Carl Zeiss Meditec, Inc, Dublin, CA). After a standard scan was obtained, tilted scans were obtained by moving the optical coherence tomography beam entrance position horizontally. The tilting angle was measured from the B-scan image, and the flattest (horizontal) and the most tilted images were selected for comparative analysis. Foveal avascular zone (FAZ) area, vessel density (VD), and vessel length density (VLD) from the superficial and deep retinal capillary plexus (SCP, DCP), and choriocapillaris flow deficits (CC FDs) were computed and compared between horizontal and tilted images. Results Thirteen eyes were excluded due to poor image quality or small angle difference (<8°) between the horizontal and tilted images. A final cohort of 27 normal eyes of 17 participants with a mean age of 39.3 ± 5.9 years was eligible for analysis. The FAZ area, VD, and VLD of both SCP and DCP were not significantly different between horizontal and tilted images. The CC FD, however, was significantly higher in horizontal images compared with tilted images (21.65% ± 2.41% vs. 21.06% ± 2.19%, P = 0.005). Conclusions CC FD measurements may be significantly affected by the position of the scanning beam and resultant scan tilting. These findings highlight the importance of capturing on-axis (pupil-centered) scans for quantitative OCTA analyses. Translational Relevance By assessing what impact a titled scan can have on OCTA measurements, this study will aid clinicians in understanding how to interpret their results in this situation.