Submission
| Title: |
Characterization of the human iridocorneal angle in vivo using a custom design goniolens with OCT gonioscopy |
| Co-Authors: |
Carmichael-Martins, Alessandra, Indiana University Bloomington; Stephen A. Burns, Indiana University Bloomington; Brittany R. Walker, Indiana University Bloomington; Brett J. King, Indiana University Bloomington |
Abstract
Background/Significance/Rationale: The trabecular meshwork (TM) and Schlemm’s canal (SC), located within the iridocorneal angle (ICA), form the main outflow pathway and a major target for glaucoma treatments. Imaging these structures is difficult due to the optical limitations of imaging through the cornea at high angles, hence most of our knowledge comes from histology and animal studies. We characterized the human ICA in vivo with Optical Coherence Tomography (OCT) imaging using a customized goniolens and a commercial OCT device (Heidelberg Spectralis).
Methods: A clinical gonioscopy lens was modified with a 12mm plano-convex lens placed on its anterior surface to focus light on the ICA structures. Each subjects’ eye was anesthetized with 1 drop of Proparacaine 0.5%. The goniolens was coupled to the eye with gonio-gel and it was held by a 3D adjustable mount. OCT volume scans were acquired on 9 healthy subjects. The linear polarization of the OCT was rotated with a half-waveplate to measure dependence of the ICA landmarks on polarization orientation.
Results/Findings: The TM was seen in 8 of 9 subjects. Polarization rotation modified the brightness of the band of extracanalicular limbal lamina (BELL) and corneoscleral bands due to the birefringent nature of the collagenous structures, increasing the contrast of SC. SC width was 99±20µm varying in size over space, including a subject with SC narrowing in the inferior-temporal quadrant.
Conclusions/Discussion: This clinically suitable gonioscopic OCT approach has successfully been used to image the human ICA in 3D in vivo, providing detailed characterization of the TM and SC as well as enhancing their contrast against their birefringent backgrounds by rotating the polarization of the imaging beam.
Translational/Human Health Impact: Clinically imaging SC will allow targeted placement of microinvasive glaucoma surgery drainage devices to improve their effectiveness. This will also increase insight into the development of glaucoma by imaging such patients.
