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Michal Laron, Mary K Durbin, Lin An, Utkarsh Sharma, Renee W Lamb, Jose G Cunha-Vaz; The Range of Foveal Avascular Zone (FAZ) Size and Vessel Density Around the FAZ in Healthy Eyes as Measured from OCT Angiography En-Face Images. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5957.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize the range of FAZ size and vessel density around the FAZ in healthy eyes, and compare manual versus automated FAZ measurements from OCT angiography en face images at different retinal layers.
Three OCT angiography scans were performed on each of 22 healthy subjects. The range of subjects’ age was 21-63 years (mean±SD; 40±10.7), and best corrected visual acuity was 20/25 or better. OCT field was 3x3 mm and vascular information was extracted by repeating each b-scan several times while evaluating change in contrast between consecutive b-scans at the same location. The average area and perimeter of FAZ in both the superficial retinal layer (SRL) and the deeper retinal layer (DRL), was calculated both manually and by using an automated algorithm.
The range of SRL FAZ area was 0.06-0.53/0.12-0.49 mm2 (automated/manual). DRL range was 0.38-0.89/0.29-1.00 mm2. SRL FAZ perimeter range was 1.07-3.21/1.21-2.47 mm (automated/aanual), and DRL range was 2.68-4.52/1.90-3.55 mm. Regression analysis comparing manual vs. automated measurements of FAZ showed high correlations for area and perimeter of FAZ in both layers (P<0.0001 for all). The correlations were higher for SRL (R2=0.87/0.85, area/perimeter), compared to DRL (R2=0.63/0.62, area/perimeter). Vessel density in the SRL was on average 19% around the FAZ, increased to 47% in the 200-400μm zone, and further increased to 58% for eccentricities beyond 400μm from FAZ border. In DRL, vessel density was on average 23% around the FAZ, increased to 44% in the 200-400μm zone, and further increased to 54% for eccentricities beyond 400μm.
Our study shows that there is a large variability in size of the FAZ in the normal population. However, the reliable identification of the FAZ both in the SRL and DRL make it a new tool to follow progression of capillary closure in retinal vascular diseases.
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