New blade design allows higher flow, greater cut rates

Take-home message: A modified vitreous cutter blade design has been found to allow surgeons a much higher flow while doubling cute rate.

By Michelle Dalton; Reviewed by Tommasso Rossi, MD

Genoa, Italy-A modified vitreous cutter blade design allows the amount of open-port surface to remain constant throughout the duty cycle, thereby giving surgeons a much higher flow while doubling the cut rate, said Tommasso Rossi, MD.

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Typical blades have asynchronous suction and cutting action that may result in limited efficiency and create issues with retinal traction, said Dr. Rossi, director of ophthalmology, San Martino Hospital, Genoa, Italy.

The new design “will increase safety and efficacy, especially with small gauge probes,” he said.

The device (Constant Flow Blade) is commercially available in Europe, and “differs from all guillotine blades so far used in vitreous cutters in that it does not completely occlude the cutting port,” he said.

The duty cycle is, therefore, at 100% “since the open surface available for suction is invariant throughout the duty cycle and the blade has a double bevel that cuts vitreous on both sided of the port during its cutting cycle,” he said.

The modified design allows for two cuts-one distal and one proximal-during each of the cutting cycles (Figure 1).

Further, the cutter can be used in any type of vitrectomy surgery, including pucker, macular hole, and retinal detachment cases.

The group has, in essence, doubled the cut rate to allow up to 12,000 cuts per minute “a frequency impossible to achieve with single-action guillotine blades.”

Study details

Dr. Rossi’s group at The Eye Hospital of Rome previously described the CFB (Twedge Cutter Blade, Optikon 2000),¹ and said the blade is by far the best-selling cutter for Optikon. In the modified design, the outer shaft has a slightly enlarged port, while the inner cylinder has a rectangular opening and double beveled blade “that slides like a cursor between the two ends of the port.”¹

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The researchers performed particle image velocimetry of the cutter probe tip and within the cutter tubing in balanced salt solution (BSS), egg albumen, and porcine vitreous. Using a high-speed camera (2,000 to 5,000 fps), the group filmed highly magnified seeded fluids to assess field velocity, volumetric flow, and fluid acceleration.

The Twedge blade (TB) achieved an average triple volumetric flow compared to a regular blade, irrespective of cut rate. Instantaneous BSS flow showed an average volumetric oscillation of 47 ml/min for the regular blade, but a much quicker 12 ml/min for the TB, “synchronous with blade action.” Both the egg white and porcine mediums confirmed a higher and steadier flow for the TB. The BSS flow rate for the traditional blade decreased linearly, likely an effect of the duty cycle reduction, but was constant with the TB, the group reported.¹

“You want a flow as stable as possible, so the mean volumetric flow should have zero fluctuation in an ideal world,” Dr. Rossi explained. “The smaller the oscillation, the more accurate the vitrectomy, and the less chance of inadvertently engaging the retina.”

Clinical relevance in today’s world

The efficiency and efficacy “are improved with triple flow and 1/10 of fluid acceleration and this allows greater safety due to less traction on the vitreous and, therefore, the retina,” Dr. Rossi said. “Less traction means safer vitreous shaving close to the retina and a faster vitrectomy due to higher flow. This, in turn, results in fewer chances of inadvertent retinal tears.”

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The group did find “some degree of velocity fluctuation,” but attributed it to a blade motion-dragging effect.

Since the port cannot be closed, when the pedal is released during the surgery, it is possible the open port can engage vitreous fibrils. That may “expose the surgeon to the theoretical risk of pulling uncut vitreous inadvertently engaged¹,” he explained.

However, in the 12 reported cases the issue was not deemed relevant, as aspiration undergoes a rapid drop once the cutting aspect is stopped.

Dr. Rossi did add that further and extensive testing should be undertaken before the new blade becomes part of the daily armamentarium.

Reference

• Rossi T, Querzoli G, Malvasi C, Iossa M, Angelini G, Ripandelli G. A new vitreous cutter blade engineered for constant flow vitrectomy. Retina. 2014;34:1487-1491.

Tommasso Rossi, MD

E:tommaso.rossi@usa.net

This article was adapted from Dr. Rossi, MD’s presentation at the 2015 meeting of the American Society of Retina Specialists. Dr. Rossi did not indicate any proprietary interest in the subject matter.