Episcleral venous fluid wave offers intraoperative guide during canal-based surgery

July 29, 2014

Observation of the episcleral venous fluid wave while performing canal-based glaucoma surgery provides intraoperative confirmation of accurate device placement, correlates with the extent of surgically induced canal cleavage, and may be a prognostic indicator for surgical success, said Ronald L. Fellman, MD.

 

(Video courtesy of Ronald Fellman, MD)

 

Dallas-Observation of the episcleral venous fluid wave while performing canal-based glaucoma surgery provides intraoperative confirmation of accurate device placement, correlates with the extent of surgically induced canal cleavage, and may be a prognostic indicator for surgical success, said Ronald L. Fellman, MD, private practice, Glaucoma Associates of Texas, Dallas.

Dr. Fellman-together with his colleague, Davinder S. Grover, MD, MPH-previously described the episcleral venous fluid wave based on observations they made in a series of four consecutive eyes undergoing combined cataract-ab interno trabeculectomy (Trabectome, NeoMedix) [J Glaucoma. 2012 Dec 31 Epub ahead of print].

During the irrigation/aspiration stage of phacotrabectome, they noted transient blanching of the nasal perilimbal and episcleral collector vessels immediately after anterior chamber balanced salt solution (BSS) surge. As the affected vessels were adjacent to the cleaved canal site, they concluded the blanching represented washout of blood by BSS flowing from the anterior chamber through the collector channels into the veins and demonstrated patency of that portion of the outflow system.

 

As a follow-up investigation, Dr. Fellman and Dr. Grover reviewed intraoperative video footage to identify and describe the intraoperative fluid wave during four types of canal-based surgery:

  • Ab interno trabeculectomy (Trabectome, NeoMedix).

  • Implantation of a Schlemm canal scaffold (Hydrus, Ivantis). (Available for investigational use only in the United States.)

  • Implantation of a micro-bypass trabecular stent (iStent, Glaukos).

  • Gonioscopy-assisted transluminal trabeculotomy (GATT).

The wave was observed in all cases and found to correspond in terms of location and extent with the surgically induced opening of the canal.

“The wave-seen as blanching of BSS through the venous plexus-was confined to the surgical site or to the type of device, thus confirming in vivo the long-held belief based on laboratory work by Chandler, Grant, Epstein, and others that there is very little circumferential flow in Schlemm’s canal,” Dr. Fellman said. “The appearance of a bleb after a filtering procedure provides glaucoma surgeons with a visible outcome marker that can help to explain the patient’s course after surgery.

 

“We believe that the episcleral venous fluid wave at least confirms that a canal-based procedure has been successful in creating communication to the collector channels and shows the collector channels are at least anatomically functioning in that area,” he continued.

In ongoing research, the investigators will be trying to determine how well the extent of the episcleral fluid wave predicts clinical success.

“Even if the surgery is technically perfect, a canal-based procedure may not help a patient whose collector channels are atrophied and not functioning,” Dr. Fellman said.

 

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