In vivo microscopy of the foveal avascular zone in normal and vasculopathic eyes

Abstract

 

Purpose

 

To map and analyze the geometrical descriptors of the foveal avascular zone (FAZ) and the tortuosity of the capillaries defining the FAZ boundaries in healthy controls and diseased eyes using the Adaptive optics scanning light ophthalmoscope fluorescein angiography (AOSLO FA).

 

Methods

 

AOSLO FA imaging was performed on 12 eyes of healthy control subjects (age mean 25, range 21-35), 4 eyes of patients with diabetic retinopathy (DR) (age mean 56, range 49-66; all treatment naïve), 4 eyes of patients with sickle cell retinopathy (SCR) (age mean 40, range 32-51; 3 treatment naïve, 1 post LASER) and 4 eyes of patients with central retinal vein occlusion (CRVO) (age mean 46, range 27-64; 1 treatment naïve, 3 post anti-VEGF). Simultaneous reflectance (790 nm) and fluorescence (488 nm) image sequences were acquired using a 1.75° field of view after oral fluorescein. Individual registered averages were tiled to create perfusion maps of the entire FAZ and its surrounding micro-vasculature. Manual delineation of the FAZ was used to calculate FAZ area (mm²), effective diameter (µm, diameter of the smallest circle to fully encompass the FAZ), perimeter (µm) and tortuosity index (TI).

 

Results

 

Results are summarized in Table 1. Area, effective diameter and perimeter showed variation among normal and diseased eyes, with the CRVO eyes having significantly higher values than controls. The highest TI was seen in eyes with DR. No difference in metrics could be made between treatment naïve and treated eyes.

 

Conclusions

 

Results concur with previous studies, and confirm the differences in FAZ geometry among normal and vasculopathic eyes. Our CRVO data corresponds with previous studies indicating that CRVO causes chronic and extensive capillary dropout resulting in a higher FAZ area, effective diameter and perimeter. The data also demonstrate that TI of DR FAZs was larger than TI of normal, SCR and CRVO eyes. As LASER and anti VEGF treatment do not seem to have an effect on the metrics, the changes in metrics over time could thus more accurately help track the pathology. The in vivo quantification of FAZ and microvascular geometry shows potential for detection and monitoring progression of vascular diseases in the eye.

 

 

Table 1

 

Keywords: 550 imaging/image analysis: clinical • 688 retina • 436 blood supply