Focused ultrasound-induced non-invasive and transient permeability of the blood-retinal barrier

Abstract

Purpose : The blood-retinal barrier (BRB) prevents the entry of harmful molecules from the blood into the neuronal space and is essential for retinal health. However, it is also a barrier to therapeutic intervention. Our goal is to deeper investigate the permeability of the BRB and develop a platform for non-invasive, transient and non-injurious increase of the BRB permeability. We use focused ultrasound (FUS) under live visualization of the retinal micro vessels and an advanced fluorescence angiography technique to analyze the results.

Methods : Our approach combines a FUS treatment with an accurate real-time analysis of the induced BRB permeability. We have designed an acoustic lens assembly for the targeted delivery of FUS into the retina of anesthetized Nile Grass rats serving as model. The FUS assembly is placed between a rodent eye and a retinal imaging microscope (Phoenix Micron IV). Continuous 1 MHz pressure waves were applied for 60 s with a peak pressure amplitude of 0.8 MPa across an area of about 1 mm². We developed an advanced fluorescein angiography method that uses an additional image registration algorithm to correct mapping errors resulting from any movement of the 3D eyeball on the captured 2D image. Through this approach, we enable a precise real-time quantification of the BRB permeability via fluorescein angiography.

Results : Sonication resulted in leakage of fluorescein into the retina under live video angiography. Significant increase in fluorescence intensity after FUS application compared with control was observed all over the retina (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 and registration software allows direct visualization of the pressure wave effects to induce BRB opening. No side effects or bleeding were noticed. In the following experiments, the range of usable and safe ultrasound amplitudes as well as the release of different fluorescein-labeled molecules will be investigated. In the long term, targeted local drug release at pathological areas of the retina will be addressed.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.