26 Episcleral Venous Fluid Wave: A Snapshot of Patency of the Trabecular Outflow Pathway The success of canal-based minimally invasive glaucoma surgery (MIGS) is dependent on the patency and function of the trabecular outflow pathway. Specifically, the collector channels downstream of nearby canal-based surgery sites must be intact and functional to enhance the flow of aqueous humor. Studies have shown that these collectors may be damaged in glaucoma,1 but currently we do not have a clinically available method to visualize these small collectors or determine their capacity. The flow through the trabecular pathway is quite complex and still poorly understood, both from an anatomic and physiological viewpoint Fig. 26.1 illustrates the attempt to map the flow of aqueous humor through the tortuous trabecular pathway, demonstrating that there are at least 11 sites of resistance along this path. We found an easy intraoperative method to visualize the patency of the nearby downstream collectors after a Trabectome procedure; we call it the episcleral venous fluid wave (EVFW).2 The characteristics of the wave of balanced salt solution that courses through the opened canal and veins represent the overall health of the nearby collector channels and tend to correlate with outcomes (Fig. 26.2). The EVFW is an intraoperative visible outcome marker, much like a bleb after a filter, that predicts the outcome of the canal-based procedure.
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