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Original Investigation |

Estimating Retinal Blood Flow Velocities by Optical Coherence Tomography ONLINE FIRST

Gerald Seidel, MD1; Gerold Aschinger, MSc2; Christoph Singer1; Sereina Annik Herzog, PhD3; Martin Weger, MD1; Anton Haas, MD1; René Marcel Werkmeister, PhD2; Leopold Schmetterer, PhD2,4; Gerhard Garhöfer, MD4
[+] Author Affiliations
1Department of Ophthalmology, Medical University of Graz, Graz, Austria
2Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
3Institute for Medical Informatics, Statistics and Documentation, Medical University of Graz, Graz, Austria
4Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria
JAMA Ophthalmol. Published online August 04, 2016. doi:10.1001/jamaophthalmol.2016.2507
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Importance  While optical coherence tomography (OCT) angiography has been considered to evaluate retinal capillary blood flow instead of fluorescein angiography, the reflectance pattern of blood vessels on structural OCT might also provide retinal capillary flow data in the absence of fluorescein angiography. This potential has been insufficiently explored, despite promising data concerning a possible relationship between the reflectance pattern of blood vessels and their perfusion velocity in a laboratory setting.

Objective  To evaluate the potential of retinal blood flow velocity estimation by structural OCT.

Design, Setting, and Participants  Cross-sectional observational study conducted from June to November 2015 at a tertiary clinical referral center. Sixty arteries (the superior and inferior temporal arteries) from 30 eyes of 30 patients (17 female, 13 male) were included in the study.

Main Outcomes and Measures  Based on the intraluminal contrast patterns of retinal arteries on OCT, 3 independent graders categorized the blood flow velocities as low, medium, or high. These results and the results from a software-based intraluminal contrast analysis were compared with the retinal blood flow velocities measured by video fluorescein angiography.

Results  Among the 30 eyes of 30 patients (mean [SD] age, 72.6 [12.3] years; 17 female, 13 male), 15 were controls without retinal occlusion, 6 had a branch retinal artery occlusion, and 9 had a central retinal artery occlusion. When discriminating between low flow velocities and medium or high flow velocities, the graders’ sensitivity ranged from 88.2% to 100% (grader 1: 88.2%; 95% CI, 63.6%-98.5%; grader 2: 88.2%; 95% CI, 63.6%-98.5%; and grader 3: 100%; 95% CI, 69.8%-100%) and their specificity ranged from 97.6% to 100% (grader 1: 100%; 95% CI, 87.7%-100%; grader 2: 97.6%; 95% CI, 87.4%-99.9%; and grader 3: 100%; 95% CI, 87.7%-100%). The κ coefficients of the comparison between the 3 graders and the angiography were 0.77 (95% CI, 0.60-0.93; P < .001), 0.64 (95% CI, 0.44-0.83; P < .001), and 0.87 (95% CI, 0.74-0.99; P < .001). In the computer-based assessment, the contrast reduction of the intraluminal pattern could be numerically expressed in a specific coefficient in the model (I2, describing the angular change of the backscattering intensity in the model), which presented nonoverlapping intervals between low flow velocities and medium or high flow velocities (mean [SD] I2, 0.3 [5.3], 20.4 [6.4], and 21.7 [4.0], respectively).

Conclusions and Relevance  This study suggests that a low retinal blood flow velocity reflects in a visually distinct contrast reduction of the intraluminal pattern of retinal vessels on OCT. Larger studies are required to assess the clinical benefits.

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Figure 1.
Schematic of Moving Erythrocyte’s Alignment in Relation to the Optical Coherence Tomographic Scan Beam

Blue arrows indicate the optical coherence tomographic scan beam; green arrows, backscattered light. The reflection is higher for perpendicular erythrocytes than for parallel erythrocytes. Adapted from Cimalla et al.3

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Figure 2.
Cross Sections of Retinal Arteries at Varying Blood Flow Velocities on Optical Coherence Tomography

The contrast of the intraluminal pattern on optical coherence tomography increased from low flow velocity (<1.5 mm/s) (A), over medium flow velocity (1.5-3.0 mm/s) (B), to high flow velocity (>3.0 mm/s) (C). D, The responsible erythrocyte alignment is schematized under each optical coherence tomographic image (adapted from Cimalla et al3). Black arrows indicate flow velocity; blue arrows, shear stress.

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Figure 3.
Semiautomated Evaluation of the Intraluminal Backscattering Profile of a Retinal Artery

Each optical coherence tomographic scan was positioned perpendicular to the temporal retinal artery. Arrow indicates the position of the scan beam. The backscattering intensity was measured at half the vessel diameter. In vessels with high flow velocity, this resulted in bimodal intensity curve modeling. AU indicates arbitrary units.

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Figure 4.
Intraluminal Backscattering Intensity Profiles According to the Angiography-Based Blood Flow Velocity Category

While the profiles in the vessels with low flow velocity were irregular (A), those with medium (B) and high (C) flow velocity exhibited a characteristic bimodal profile. This pattern also seemed more pronounced in vessels with higher velocities within a single category. Dashed lines indicate mean backscattering intensity for each category; AU, arbitrary units.

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Figure 5.
Erroneous Intraluminal Backscattering Evaluation

In 1 artery with high blood flow velocity, the scan position (arrow) at a bend close to a retinal vein resulted in low contrast in the inferior half of the vessel and a lacking middle hump on the intensity profile. AU indicates arbitrary units.

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