title: Estimating Retinal Blood Flow Velocities by Optical Coherence Tomography.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  METHODS
  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
  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.
authors.affiliation: Department of Ophthalmology, Medical University of Graz, Graz, Austria.
authors.forename: Gerald
authors.initials: G
authors.lastname: Seidel
authors.affiliation: Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
authors.forename: Gerold
authors.initials: G
authors.lastname: Aschinger
authors.affiliation: Department of Ophthalmology, Medical University of Graz, Graz, Austria.
authors.forename: Christoph
authors.initials: C
authors.lastname: Singer
authors.affiliation: Institute for Medical Informatics, Statistics and Documentation, Medical University of Graz, Graz, Austria.
authors.forename: Sereina Annik
authors.initials: SA
authors.lastname: Herzog
authors.affiliation: Department of Ophthalmology, Medical University of Graz, Graz, Austria.
authors.forename: Martin
authors.initials: M
authors.lastname: Weger
authors.affiliation: Department of Ophthalmology, Medical University of Graz, Graz, Austria.
authors.forename: Anton
authors.initials: A
authors.lastname: Haas
authors.affiliation: Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
authors.forename: René Marcel
authors.initials: RM
authors.lastname: Werkmeister
authors.affiliation: Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria4Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria.
authors.forename: Leopold
authors.initials: L
authors.lastname: Schmetterer
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Garhöfer
mesh_terms: D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D005451:Fluorescein Angiography; D005654:Fundus Oculi; D006801:Humans; D008297:Male; D012039:Regional Blood Flow / Q000502:physiology*; D015203:Reproducibility of Results; D015356:Retinal Artery Occlusion / Q000175:diagnosis / Q000503:physiopathology*; D012171:Retinal Vessels / Q000503:physiopathology*; D041623:Tomography, Optical Coherence / Q000379:methods*; D014792:Visual Acuity