Quantitative Mapping of Uveoscleral and Lymphatic Drainage Pathways From the Suprachoroidal Space

Abstract

Purpose : This study quantitatively evaluates the tracer distribution and drainage following suprachoroidal (SC) injection using a near-infrared (NIR) fluorescent tracer and Magnetic Resonance Imaging (MRI).

Methods : A NIR fluorescent tracer, CF770 conjugated with bovine serum albumin (MW:70kDa, 0.5μL) was injected into the SC space of the right eye of adult mice (C57BL/6; n=6). Non-injected left eyes (n=6) were used as controls. Mice were sacrificed 20 minutes post-injection. Infrared reflectance and fluorescence images of the neck lymph nodes were obtained using a scanning laser ophthalmoscope (Spectralis, Heidelberg Engineering, Germany). Orbit specimens were processed and serially sectioned with a cryostat. Frozen sections were imaged using NIR epifluorescence microscopy mounted with sCMOS camera. The mean pixel intensities (MPI) were measured in the sclera and orbital tissue using ImageJ (NIH, v1.53q). Wilcoxon and student’s t-test were used for statistical analysis. A second set of adult mice (C57BL/6; n=2) received SC injection of galbumin (human serum albumin conjugated with gadolinium and rhodamine; MW:70kDa; 0.5μL, BioPAL, USA) into the right eye. In vivo MRI scans were collected for 50 minutes with a 7T pre-clinical scanner (BioSpec 70/30 USR, Bruker BioSpin) covering the orbits. A 3D fast low angle shot sequence was used, and images were reconstructed using the 3D Slicer software.

Results : 20 minutes after tracer injection into right eye, the MPI of the NIR fluorescent signal within the right sclera was greater compared to left sclera (3.592±4.230 vs. 0.031±0.002, right and left sclera respectively; p=0.0244). The tracer signal was also greater in the right orbit compared to left orbit (7.359±1.965 vs. 0.028±0.006, right and left orbit respectively; p=0.0025). In vivo MRI scans demonstrated that tracer drains through the medial pathway into the orbit. Ex vivo NIR fluorescent imaging showed that tracer drains into the right accessory submandibular lymph node.

Conclusions : This study provides the first quantitative evidence that SC tracer injection exits the eye through a medial route into the orbital tissue and drains into the neck lymph node. This new multimodal imaging approach may lead to in vivo quantitative assessment and screening of drugs targeting the uveoscleral/lymphatic drainage pathway for the treatment of glaucoma and other eye diseases.

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