Change the Channel, Please!

As a glaucoma surgeon, imagine if you could visualize aqueous outflow in the trabecular meshwork (TM) with something like OCT? Such information would help guide your choice of procedure, device (and placement of the device), and increase your confidence in getting a good post-procedural outcome. Of course, such a device would have research applications too, generating great insight into the pathologies present in many forms of glaucoma, potentially yielding new knowledge about the disease that could result in earlier – and smarter – interventions.

At the recent 2018 American Glaucoma Society meeting, Murray Johnston, a Clinical Professor at the University of Washington in Seattle presented on just that (1): a pilot study of a “very high resolution” OCT-based imaging method that could – in ex vivo human eyes with cannulated Schlemm’s canals – detect motion in the TM, the dynamic collector channel entrance (CCE), and deep intrascleral collector channels. The method could also show CCE closure or disruption by MIGS devices or approaches, which could affect distal resistance and, ultimately, the success of the procedure.

According to Johnstone, the speed at which the collector channels can respond to pressure changes from 0–30 mmHg is “remarkably fast” – in the region of 150 ms – and there was a “marked synchrony” between collector channels and Schlemm’s canal in non-glaucomatous eyes – but in glaucomatous eyes, this relationship is lost, and aqueous movement is far slower. And the technique comes with an additional advantage: it should be able to flag those patients with very advanced disease who are unsuitable for Schlemm’s canal-based procedures; not only could it spare patients from a procedure that cannot benefit them, but it would also have the added benefit of increasing the efficacy of the MIGS procedures in those patients who can receive them.

What might the future bring? Intra-operative cannulation combined with OCT-based visualization of the trabecular meshwork and collector channels – or even an entirely non-invasive approach when the technology is mature enough: phase-based OCT to identify areas of poor motion in Schlemm’s canal, occlusions in ostia, and similar pathology. It looks like it’s only a matter of time before ophthalmic surgeons start using this technology to provide individualized care for patients with glaucoma.