In vivo microscopic spatial characterization of foveal microvasculature in healthy human subjects

Abstract

 

Purpose

 

To characterize the topography of foveal vessel density in healthy human subjects using adaptive optics scanning light ophthalmoscope fluorescein angiography (AOSLO FA).

 

Methods

 

Ten eyes of 6 healthy subjects (mean age 23.2±1.5 years old) were imaged using AOSLO FA after oral fluorescein administration. Simultaneous reflectance (790nm) and fluorescence (488nm) image sequences were acquired using a 1.75° field of view. Registered averges were tiled together to create perfusion maps centered at the fovea (Fig.1A). Maps were then skeletonized and overlaid by a grid of equiangular octants and 8 consecutive annuli (A), 100 µm thick, centered at the fovea (Fig. 1B).The grid was centered on the manually determined center of the darkest area of foveal avascular zone (FAZ) on reflectance AOSLO. Here, we report vessel density (mean±SD) by pooling the annuli within each octant into two regions; A1 (200-400μm) and A2 (400-800μm), chosen to minimize the effect of the FAZ (0-200μm) and because of a radial vessel density plateau at 400μm.

 

Results

 

Mean vessel density at A1 was 24.3±6.4mm^-1 while at A2 was 50.8±3.1mm^-1 (n=10). Despite small inter-octant differences (<10%), statistically significant inter-octant variability was found (two way ANOVA; F(7)=3.65, p<0.005), with highest A2 vessel densities recorded at the superior and inferior octants and lowest at nasal and temporal octants (Fig. 2). Significant inter-subject variability was found (two way ANOVA; F(5)=7.85, p<0.00001), while vessel density differences between fellow eyes were found not to be significant (t(4)=-0.43, p=0.69).

 

Conclusions

 

The vascular density normative data presented here and the successful systematic identification of all capillaries within the foveal region is a first step towards developing highly sensitive quantitative bio-markers of ocular and systemic disease that affects the retinal vasculature.

 

 

Fig. 1. AOSLO FA foveal map (A) and its skeleton after binarization and thresholding (B).

 

 

Fig. 2. A1 and A2 mean vessel densities across different octants. (N: Nasal, T: Temporal)

 

Keywords: 688 retina • 550 imaging/image analysis: clinical