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Yi-Sing Hsiao, Ben K Jang, Tony H Ko, Kelly Soules, Qienyuan Zhou; Measurements on Vessel Length Density and Fovea Avascular Zone Area with OCT-Angiography: a Repeatability Study using AngioVue. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1646.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the repeatability of measurements on vessel length density and fovea avascular zone (FAZ) area using OCT-Angiography (OCTA) en face images acquired with AngioVue software on an Avanti SD-OCT system (Optovue, Inc., Fremont, CA).
12 normal subjects (age 26-60, 4 female and 8 male) were enrolled in this study with informed consent. Each subject was imaged at an internal site by a single operator on an Avanti SD-OCT system using AngioVue software with 3 replicates of Angio Retina scan pattern. The scan area was all 3 mm × 3 mm. Analyses were performed on OCTA en face images generated from superficial and deep retinal layers with average and maximum intensity projection (MIP) methods. The images were first skeletonized and vessel length density was calculated in the entire en face image and four parafoveal sectors. The parafoveal sectors were defined similar to ETDRS chart, but with a diameter from 1 mm to 2.5 mm. The four sectors are tempo (T), superior (S), nasal (N), and inferior (I) (Fig. 1). The size of the FAZ was also calculated. No manual corrections were applied for all analyses. Repeatability was calculated in terms of standard deviation and coefficient of variation (COV).
Table 1 summarizes the average vessel length density and corresponding COV. The vessel length density is higher in the deep layer (24-29 mm-1) as compared to the superficial (19-25 mm-1). Average COV is 3-6%. Table 2 shows the results for FAZ area measurement. The FAZ area varies across normal subjects with a minimum and maximum size of 0.25 and 0.51 mm2 (superficial layer, average projection). The within-subject variation (S.D.) is between 0.03-0.04 mm2 and the average COV is 6-9%.
OCTA en face images generated by AngioVue provide high-resolution vasculature detail which allows the measurements on the vessel length density and FAZ area. This study shows good repeatability in both measured parameters for normal subjects.
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