Non-Invasive Imaging of Inner vs. Outer Vessel Diameter in the Mouse Eye

Abstract

Purpose: : Retinal blood vessel diameter and arteriovenous ratio (AVR) are useful diagnostic parameters in clinical ophthalmology. The low optical density of vascular walls precludes their direct visualization in routine fundoscopy and clinical AVR estimation is based on the lumen but not the entire vessel diameter. Here we used a transgenic mouse model to quantify total vessel dimensions (wall and lumen) in vivo and to determine AVR based on inner vs. outer diameter.

Methods: : Confocal scanning laser ophthalmoscopy (cSLO) of the retinal vasculature was performed in wild type and transgenic mice expressing green fluorescent protein (GFP) under the transcriptional control of the smooth muscle type α-actin (αSMA) promoter. Spectral-Domain-OCT (SD-OCT) and ERG was performed to control for integrity of retinal structure and function in vivo and histology to demonstrate location of GFP expression.

Results: : SD-OCT and ERG testing demonstrated intact retinal structure and function. Native cSLO imaging and indocyanine green angiography yielded inner vessel diameters similar to clinical fundoscopy. In αSMA-GFP mice, autofluorescence imaging of the GFP-marked vascular walls allowed to determine outer vessel diameters. The mean AVR based on either inner diameter (0.72 ± 0.08, mean ± sd) or outer diameter (0.97 ± 0.09) measurements were significantly different (p < 0.01).

Conclusions: : Retinal vessel outer diameter was accessible in αSMA-GFP transgenic mice in vivo. The inclusion of vessel wall width in the AVR calculation reflects the dimensions of the entire vessel and results in a more accurate AVR estimation. Since vessel walls are primary targets of pathologic changes in common hypertensive and metabolic diseases, αSMA-GFP transgenic mice may prove valuable in the detailed assessment of such disorders in vivo.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retina • imaging/image analysis: non-clinical