New Surgical System Features Performance-enhancing Technology
Learn how the CONSTELLATION® Vision System facilitates vitreoretinal surgery.
BY JOHN C. HUCULAK
During the 2008 annual meeting of the American Academy of Ophthalmology, Alcon introduced its all-new CONSTELLATION® Vision System for retinal surgery to U.S. retinal specialists. The system features a 5000 cuts per minute (cpm) vitrectomy probe with duty cycle control, integrated pressurized infusion with IOP control, advanced xenon illumination and an embedded 532-nm laser.
Here is a look into the technology behind the new system's capabilities in 3 key areas: infusion, cutting and aspiration. Technological advances in these areas combine to improve intra-operative fluidic stability, decrease tissue movement during vitrectomy and membrane dissection and reduce length of pull on tissue as it is drawn to the cutting port.
Integrated Pressurized Infusion and IOP Control
The CONSTELLATION® Vision System monitors infusion pressure and makes adjustments to stabilize IOP during retina surgery. As infusion fluid flows into the globe, the system automatically anticipates the resulting pressure drop that builds across the infusion cannula as fluid flows through. The infusion pressure is automatically increased to match and compensate for the pressure drop across the infusion cannula, effectively canceling out the negative effect of the infusion cannula pressure drop. This keeps IOP constant, within 2 mmHg, throughout the entire procedure.
It is anticipated that by using this new system, surgeons will be able to lower average IOP levels during surgery. Surgical complications, such as poor visualization (through a deformed cornea resulting from low IOP), retinal arterial bleeding and choroidal detachment can be more easily avoided by the improved IOP regulation.
Ultrahigh Cutting Rates
The advanced ULTRAVIT® Vitrectomy Probe technology in concert with the CONSTELLATION® Vision System enables vitrectomy and membrane dissection at previously unattainable cut rates and port open duty cycles. The ULTRAVIT® Probe pneumatic design has drawn from the best features of the ACCURUS® and INNOVIT® Probes and incorporated all-new patented technology as well.
The ULTRAVIT® Probe with dual actuation line technology makes the spring return mechanism approach used in other vitrectomy probes obsolete. The conflicting design requirements of the return spring had been a primary factor in limiting maximum cut rates in the past. The design of the new probe includes an integrated double-sided diaphragm with dual actuation lines (Figure 1). Air pressure first pushes against the backside of the diaphragm, which causes it to move toward the tip of the probe. The cutter, connected to the diaphragm, is driven through the port to make the cut. Alternating air pressure on the other side of the diaphragm, while venting pressure on the backside, pushes the cutter back into place, reopening the port.
Figure 1. A cross section of the ULTRAVIT® Vitrectomy Probe shows its double-sided diaphragm with dual drive lines. Dual alternating air pulse pressure is utilized to create the probe's cutting action.
The new probe technology provides for ultrafast cut and return action, enabling the cut cycle to be completed very quickly. A cut cycle that quickly completes can be repeated more frequently than with previous designs, allowing surgeon-controlled cut rates up to 5000 cpm.
The ULTRAVIT® Probe is the first vitrectomy probe designed for small gauge from the ground up. The probe is available in 20-, 23- and 25-g formats and can be configured for additional gauge sizes, reducing the time it takes to develop new gauge formats.
To create a new gauge format, the needle and cutter are exchanged for the new size and the appropriate color-coded handle is snapped in place. The design platform can readily accommodate even smaller gauge formats, such as 27 g.
The ergonomics of the probe are notable as well. The grip area on the front end of the handle is covered with a soft rubber compound. Also, surgeons who prefer the feel of a shorter-handled ACCURUS® probe-like instrument can remove the back section of the probe body.
Duty Cycle Control
In addition to enabling ultrahigh cut rates, the dual actuation technology of the ULTRAVIT® Probe provides increased port open duty cycles, greater than 50% at 5000 cpm, and offers an alternative to conventional thinking about cutting and duty cycle. By merging advanced probe technology with new CONSTELLATION® Vision System probe driver technology, duty cycle — the percentage of time the port is unobstructed by the cutter — is maximized and can be controlled. Since the port is opened and closed with air pressure pulses, and there is no returning spring, the port open characteristic of the duty cycle can be inverted. Rather than driving the probe with a port open bias, for high-flow efficiency, the probe can be driven where the port is biased closed instead. A biased closed port reduces flow rate for a given vacuum level and can be used to delicately dissect membranes close to detached retina. Three duty cycle profiles are available with the system, port biased open, port biased closed and a fixed 50% duty cycle for surgeons who prefer constant duty cycle cutting.
Furthermore, based on the type of tissue being cut and removed, the surgeon can modify the duty cycle to control flow, independent of vacuum and cut rate. The increased efficiency of the system's technology allows flow rates of 8 cc per minute or better at a 5000 cpm cut rate regardless of what gauge is being employed (Figure 2). With appropriate vacuum settings, the surgeon can achieve the same aspiration rate experience and the same flow efficiency at any of the 3 gauges. For example, in a 20-g procedure, flow is 8 cc per minute, using 200 mmHg of vacuum at 5000 cpm. In a 23-g procedure, flow is 8 cc per minute, using 300 mmHg of vacuum at 5000 cpm. And in a 25-g procedure, flow is 8 cc per minute, using 650 mmHg of vacuum at 5000 cpm.
Figure 2. The increased flow efficiency of the combined CONSTELLATION® Vision System and the ULTRAVIT® Probe results in flow rates of 8 cc per minute or better at 5000 cuts per minute, regardless of what gauge is being employed.
Aspiration Flow Limit
Another key aspect of the CONSTELLATION® Vision System's advanced fluidics is the aspiration flow limit feature. When performing a 20-g procedure, the surgeon can select an aspiration flow limit from 0 to 20 cc per minute. This limit is independent of vacuum level. Once flow reaches the set limit, the system intervenes to prevent the flow from exceeding that limit.
This feature can be loosely compared to computerized traction control on a car. When the car hits a patch of ice (or a flow obstruction breaks away from the probe tip and flow increases, as can happen when attempting a posterior hyaloid detachment), the anti-lock brakes take over (or the CONSTELLATION® system automatically reduces the vacuum, which reduces the flow). When the car moves off the ice (or the posterior vitreous is re-engaged), control is returned to the driver (and the surgeon can re-engage the posterior vitreous and continue the posterior hyaloid detachment).
New Level of Performance
In addition to the features highlighted here, the CONSTELLATION® Vision System incorporates improvements in virtually all aspects of surgical functionality and performance. With its easy to use V-LOCITY® Efficiency Features, efficient tissue dissecting capabilities and advanced fluidics, the system enables surgeons to optimize the efficiency of their preferred surgical techniques.
John C. Huculak is senior director of research and development for Alcon Laboratories Inc.