Characterization of the human iridocorneal angle in vivo using OCT Gonioscopy

Abstract

Purpose : To characterize the human iridocorneal angle (ICA) in vivo with gonioscopic Optical Coherence Tomography (OCT) imaging using a customized goniolens and a clinically available OCT device (Heidelberg Spectralis). The trabecular meshwork (TM) and Schlemm’s canal (SC) located within the ICA are the target for many glaucoma treatments. However, in vivo study of the TM and SC lying at the apex of the ICA is difficult, and most of our knowledge comes from human post-mortem or animal model studies.

Methods : A clinical single-mirrored gonioscopy lens was modified with a 12mm button lens placed on its anterior surface to provide an image plane at the approximate distance of the ICA structures. The subjects’ eye was anesthetized with 1 drop of Proparacaine Hydrochloride USP 0.5% . The goniolens was placed on the eye coupled with gonio-gel and aided by a 3D adjustable mount fixed to the head mount of the OCT device to provide additional stability. The waist of the OCT beam was set to fall on the goniolens mirror and steering was available by tilting the OCT device. Radial and tangential dense OCT scans with minimum spacing were performed on 6 young healthy subjects and 1 with pigment dispersion syndrome, focused on the inferior ICA apex.

Results : The TM was seen in all 7 subjects showing more detailed structure of the uveoscleral meshwork, with an average signal penetration depth of 636±116 µm (signal dropped to 2x the noise level). Schlemm’s canal was seen in 4 subjects. The penetration depth was 560 µm through the TM and SC for one subject. Schlemm’s canal size varied rapidly over space, with the cross-sectional area varying 35% between individual b-scans tangentially and 19% radially.

Conclusions : OCT gonioscopy imaging of the human ICA in vivo has been proved successful, providing both sufficient resolution to depict the structure of the uveoscleral meshwork, and penetration depth past Schlemm’s canal.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

 

Cross-sectional images of the ICA reconstructed from a radially oriented OCT dense scan, including b-scan (green), orthogonal (blue) and enface (red) views.

 

OCT b-scans of the ICA focused on A) the uveoscleral meshwork for a subject with pigment dispersion syndrome and B) the ICA apex showing the TM, SC and iris structures.