Examination of parafoveal intercapillary region with axial length and foveal avascular zone size in healthy adults

Abstract

Purpose : It is unclear whether the topography of the foveal microvascular network is related to an eye’s size or foveal properties. We sought to better understand the geometry of parafoveal intercapillary regions (PICRs), or regions between capillaries, surrounding the foveal avascular zone (FAZ) and determine whether PICR properties are related to an eye’s axial length or FAZ structure.

Methods : Adaptive optics scanning laser ophthalmoscope images of the perfused superficial capillary plexus were acquired around the FAZ in right eyes of 13 healthy adults (mean age = 26.8 ± 3.9 years). Retinal capillaries were automatically segmented from perfusion images using a convolutional neural network and manually corrected for minor segmentation errors. A custom MATLAB program delineated the FAZ boundary and computed FAZ area and circularity. The program also delineated all PICRs and computed PICR area and circularity, as well as the minor axis and axis ratio (major to minor axis) from an ellipse best-fit to each PICR, for PICRs whose centroid was located inside annuli of 100, 200, and 300 µm from the FAZ border.

Results : Mean axial length was 23.75 ± 1.09 mm (range: 22.57-26.18 mm) and mean FAZ area was 0.25 ± 0.10 mm² (range: 0.04-0.38 mm²). PICR minor axes within the 100 µm annulus (mean ± SD: 61.8 ± 10.0 µm) were significantly larger than within the 300 µm annulus (46.3 ± 4.1 µm) (Kruskal-Wallis One Way AVNOVA on ranks, Dunn’s Post-hoc, P<0.05), but not the 200 µm annulus (50.8 ± 5.1 µm). There were no correlations between PICR metrics and axial length. PICR area and minor axis were not related to FAZ area. However, for 200 and 300 µm annuli, eyes with smaller FAZ areas had more circularly-shaped PICRs, as evidenced by increased values of PICR circularity (r²=0.33, P=0.04 and r²=0.43, P=0.02, respectively) and decreased axis ratios (r²=0.35, P=0.03 and r²=0.33, P=0.048, respectively). Eyes with more circular FAZs had larger PICR major and minor axes (r²=0.41, P=0.02 and r²=0.45, P=0.01), larger PICR areas (r²=0.43, P=0.02), and decreased PICR circularity (r²=0.32, P=0.04) for the 100 µm annulus.

Conclusions : PICR geometry is not related to axial length, suggesting factors other than retinal stretching drive intercapillary spacing (e.g. metabolic demand). The relationships between PICR geometry and FAZ area and shape should also be considered when calculating vascular density around the FAZ.

This is a 2020 ARVO Annual Meeting abstract.