[Area of the foveal avascular zone in patients with refractive errors]

To investigate the dependence of the area of the foveal avascular zone (FAZ) on axial eye length (AL) and to develop a feasible method for correcting this dependence.

The study involved 209 patients over the age of 18 years (209 eyes), of them 52 patients with AL of 20-22 mm (hyperopia group), 60 patients with AL of 25.5-28.5 mm (myopia group) and 97 patients with AL of 22.5-24.5 mm (emmetropia group). Optical coherence tomography angiography (OCTA) examination was performed on Cirrus HD-OCT 5000 with AngioPlex («Carl Zeiss Meditec», Germany).

FAZ area was corrected using the Littmann-Bennett formula modified by A.A. Shpak and M.V. Korobkova. FAZ area values both in emmetropic patients and in patients with refractive errors varied over a very wide range. Before correction, AL had a significant influence on the FAZ area (mm²), which compared to the emmetropia group (0.27±0.09) was significantly reduced in the myopia group (0.21±0.07; p<0.000) and increased in the hyperopia group (0.31±0.11; p=0.015). The corrected FAZ area values did not differ in the compared groups. After correction the FAZ area decreased on average by 19% in the hyperopia group and increased by 25% in the myopia group. A chart and an Excel (Microsoft)/LibreOffice Calc program have been developed for correction of the FAZ area depending on the AL.

Refractive errors, especially high-degree ones, have a significant effect on the FAZ area. This study proposes an original chart and a calculation program for correct interpretation of FAZ area measurements in patients with refractive errors, providing an accessible and quick way to assess the obtained results.