Quantitative assessment of foveal vascular bed

Purpose of the study — to determine the causes of significant differences in optical coherence tomography angiography (OCTA) quantitative metrics in the central zone and the inner ring of the ETDRS grid and to develop methods for their correcting.

Material and methods. Manuals for the most common OCTA devices of various manufacturers Carl Zeiss Meditec (USA), Optovue (USA), Topcon Corp. (Japan), Optopol Technology (Poland), Huvitz Co. (South Korea) were studied. OCTA data of 57 people (57 eyes) over 18 years old with refraction close to emmetropia were analyzed. OCTA examinations were performed on a Cirrus HD-OCT 5000 device (Carl Zeiss Meditec, USA). The perfusion density, vessel density and foveal avascular zone (FAZ) area of the superficial capillary plexus were determined. OCTA images of the macula were acquired using the 6 × 6 mm scan.

Results. It was found that in most devices, including Cirrus HD OCT, the calculation of indicators in the central zone of the ETDRS scheme d = 1 mm is performed by dividing by the entire area of the central zone without taking into account the area of the FAZ. As a result, the quantitative metrics of the central zone are significantly underestimated. A correction formula has been proposed to calculate OCTA parameters adjusted for the size of the FAZ. It has been shown that the correction increases the quantitative metrics of the superficial capillary plexus in the central zone of the ETDRS grid by about 1,5 times, approaching their values to the indicators in the inner ring of the ETDRS grid.

Conclusion. Correcting the values to account for the FAZ area provides more accurate characterization of the quantitative OCTA indicators in the central zone.

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