Real-time monitoring of the focused ultrasound-induced permeabilization of the blood-retinal barrier

Abstract

Purpose : The Blood-retinal barrier (BRB) prevents the entry of harmful molecules from blood to enter the neuronal space and is essential for retinal health. However, it also poses a hurdle for entry of therapeutics. Our goal is to develop a platform for non-invasive, transient and non-injurious increase of the BRB permeability. We use focused ultrasound (FUS) to deliver pressure waves under live visualization of the retinal micro vessels. Angiography will allow quantification of the BRB permeability in real-time. Computational modelling of the BRB will be used to optimize the parameters surrounding our technologies.

Methods : Our approach combines in vivo animal experiments with computational modeling. We performed in vivo-experiments and used the results to optimize the computer model iteratively. We developed a prototype acoustic lens assembly based on numeric simulation (Comsol Multiphysics) for the delivery of FUS pressure waves to targeted regions in the BRB. Our acoustic lens assembly is designed to be placed between a rodent eye and a retinal imaging microscope (Phoenix Micron IV). Sonication experiments in anesthetized Nile grass rats caused leakages of fluorescein dye into the retina under live video microscopy. The parameters were continuous 1 MHz pressure wave delivery for 60 s with a peak rarefactional pressure (PRFP)-amplitude of 0.8 MPa.

Results : Significant increase in fluorescence intensity up to factor two after FUS treatment compared with control was observed (P << 0.001; Kruska-Wallis H-test). 24 h post sonication the BRB leakage returned to normal baseline levels. Histology showed no sign of acute injury.

Conclusions : Our acoustic lens assembly allows direct visualization of pressure wave induced BRB opening in vivo for the first time. At the indicated PRFP, the opening is non-injurious and reversible back to normal levels.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.