In Vivo Visible-light Optical Coherence Tomography for Imaging the Full 360 Degrees of the Conventional Outflow Pathway

Abstract

Purpose : Glaucoma is most often a result of increased outflow resistance within the conventional aqueous humor outflow (AHO) pathways (consisting of trabecular meshwork (TM), Schlemm’s canal (SC), and collector channels (CC)). Thus, noninvasive imaging of the AHO pathways has the potential to optimize the efficacy of glaucoma treatments. We utilized robotic visible-light optical coherence tomography (vis-OCT) to image the AHO pathways 360 degrees around the eye.

Methods : To image the circumferential AHO pathways, we acquired multiple volumetric OCT volumes around the limbus of the eye. Using a simultaneous localization and mapping method, we mapped each OCT volume into a common coordinate system. We reconstructed the entire AHO pathways and characterized SC morphology, CC distribution and morphology. Variations in these parameters after IOP modulation and pilocarpine administration were characterized. To validate whether segmental differences in these parameters had any clinical relevance, we implemented a resistor model of outflow resistance and tested whether segmental differences had the potential to influence surgical outcomes.

Results : We found that using our robotic OCT to image conformal to the AHO as compared to fixing the sample arm at a rigid position improved the contrast-to-noise ratio between SC and TM by 32.4 dB. Segmental distribution of CC was observed, with the quadrant with the most CC having 2.3 ± 0.6 times the number of CC as the quadrant with the least CC in a sample of six C56BL/6 mice. Mathematical modeling using the CC distribution from these mice predicted that the location of iStent surgery relative to the CCs could influence IOP reduction by up to 53% of the mean reduction at all positions.

Conclusions : We reconstructed the entire AHO pathway in vivo in mice utilizing vis-OCT’s high axial resolution. Further studies using OCT will deepen our understanding of conventional AHO pathway physiology.

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

 

Digitally resampled CCs around the 360 degrees of the eye. The blue arrows point to SC and the green arrows to CCs. Each CC is sorted by location (N for nasal quadrant, S for superior quadrant, T for temporal quadrant, and I for inferior quadrant). Scale bar is 50 µm.

 

3D reconstruction of the SC within the anterior segment of the eye. SC is seen as a continuous orange structure and the anterior segment is the grayscale volume containing SC. Scale bar is 100 µm.