Early data from an international feasibility study of a laser-titratable tube shunt indicate that the system is effective and safe in patients with moderate to severe glaucoma. Arsham Sheybani, MD, presented 3-month data from the study of the Calibreye Titratable Glaucoma Therapy surgical system (Myra Vision, Inc) during the American Glaucoma Society’s meeting in Washington, DC.

The Calibreye device is made of silicone and is about 10 mm long, said Dr. Sheybani, an associate professor of ophthalmology and visual sciences at the Washington University School of Medicine in St. Louis who is a consultant to Myra Vision (Figure 1). It contains 3 flow channels that connect the anterior chamber and subconjunctival space. The middle lumen, called the standard channel, is always open, while 2 other channels (the medium and large lumens) are controlled by nitinol valves in the anterior chamber that are directly visible through the peripheral cornea. These valves contain paddles that can be opened or closed using a green wavelength laser at the slit lamp after implantation, providing 4 different adjustable settings to modulate aqueous flow resistance, and therefore IOP. “Depending on which channels are opened, we can modify the flow state,” he explained. “So the original baseline is going to give high single digit backstop pressure, all the way down to low single digit pressure in theoretical calculations.” Dr. Sheybani noted that, based on testing to date, the channels can be opened or closed with the laser as many times as needed.

The ongoing feasibility study is a prospective, nonrandomized open-label trial that has enrolled 43 patients across four clinical sites in India, Mexico, and Panama. Dr. Sheybani presented data on 33 patients who had completed at least 3 months of follow-up. Eight of these patients had previously failed subconjunctival incisional surgeries, he said. The study data showed a 44.9% reduction in IOP compared to baseline, with an average postoperative IOP of 12.1 mmHg. Additionally, 88% of patients were medication-free, with an overall mean reduction of more than three medications per patient.

Safety data was “pretty much what you would expect,” noted Dr. Sheybani. He did note that in 1 case the device had to be explanted due to hypotony maculopathy. “It was very early, during our first implants,” he said. “When we went to explant, it was obvious that there was peritubular flow around the device.” As a result, the surgeons changed the implantation technique for subsequent cases to avoid this potential issue.

One of the advantages of this titratable system is that, unlike a trab, the surgeon can use the laser to make an adjustment if the pressure drops so low that the patient is at risk of hypotony. Dr. Sheybani provided several case examples from the study, including one subject whose baseline IOP was 30 mmHg. “The subject required 2 laser treatments to increase flow, but at 1 month the pressure was down to 4 mmHg with early signs of hypotony,” he said. “So lasers were applied to close off 1 of the channels and there was an immediate in-office response. At 3 months, the patient’s pressures was back up to 13 mmHg, so the channel could be reopened at that time point.”

“I’m not really going to conclude about the IOP effectiveness,” he continued. “It surely works in 3 months. But really, what we’re looking at is, can we change or modify the pressure instantaneously with laser? That was done literally every time that we tried. There was at least some response, and the paddles were able to manipulate it to change the pressure.” GP