Comparison of Two Spectral-domain Optical Coherence Tomography Scan Modes for Measuring Retinal Vessel Diameter

Purpose: To assess the agreement between Line 3-5 raster scan mode and circular scan mode for measuring retinal vessel diameter, and to analyze the influence of scanning distance on retinal vessel diameter and agreement.Methods: 79 healthy participants (79 eyes) were scanned with two modes. The scanning distance was defined as the distance from the center of the optic disc to the intersection of the blood vessel and the scan line on the raster image. The large superior temporal vessel was measured, with the distance between vascular wall hyperreflectivities measured to obtain vessel diameters. The degree of agreement between the line 3-5 raster scan and circular scan modes, and the effect of scanning distance on agreement and vascular diameter were assessed.Results: There was good agreement between line 3 subgroup and the circular scan for measuring venous and arterial diameter (venous: intraclass correlation coefficients (ICCs) = 0.87, p < .001; arterial: ICCs = 0.84, p < .001). Unexpectedly, diameters from the fourth raster scan were only comparable to the circular scan in measuring venous diameter (ICCs = 0.86, p < .001), despite the same scanning distance between the fourth raster line and circular scan. Vessels with a scanning distance between 1400 μm - 1799 μm showed good agreement with the circular scan (venous and arterial: all ICCs ≥ 0.84, p < .001). In addition, venous diameter and arterial diameter decreased with increasing distance from the optic disc center, with venous and arterial diameter decreasing by 0.02 μm/μm (p < .001) and 0.007 μm/μm (p = .02), respectively.Conclusion: Arterial and venous diameter measured by the circular mode was comparable to only one scan line and two scan lines of the raster scan mode, respectively. Our study identified a difference between the two scan modes, with the difference not fully attributable to differences in scanning distance. Prospective studies reporting vascular diameter as a primary outcome should report the scan mode used.