High-speed Cutting with Stable Fluidics
High-speed Cutting with Stable Fluidics
Surgeons discuss the performance of the Stellaris PC for critical aspects of vitreoretinal surgery.
Dr. Heier: Let's talk about our experiences with the Stellaris PC cutter. What are your thoughts in terms of the cut rate efficiency and how it works for core vitrectomies vs. shaving?
Dr. Blinder: At first I did not see a need for a higher cut rate, but after using the Stellaris PC, I actually see a great advantage. I recently did a retinal detachment procedure where I set the cutter at 5000 cuts per minute (cpm) and, while varying the aspiration, did the entire core and the vitreous base trimming at the same 5000 cpm. The fluidics at 5000 cpm are very good. The flow rate does not decrease at the higher cut rate. I saw minimal movement of the detached, mobile retina during the entire vitrectomy.
I also like the high volume reflux function. It is 3 times greater than the Millennium Microsurgical System. One very efficient aspect of this function is using it when we are done with Kenalog to flush it out of a macular hole or off the surface of the retina.
Dr. Tewari: The reflux is a wonderful tool when working on diabetic cases. I recently did a diabetic tractional detachment with multiple areas of active neovascularization using the Stellaris PC. Once the membrane dissection was complete, there were a few areas of residual bleeding from the neovascular fronds. These areas can ooze and can lead to postoperative vitreous hemorrhage. With the older vitrectomy machines, the reflux on the vitrector was not impressive, especially with small-gauge platforms. In contrast, the Stellaris PC reflux cleared the blood very quickly and efficiently. It was very robust, and I was able to take the intraocular diathermy and treat those areas precisely. At the end of the case, the areas were well treated and there was no postoperative hemorrhage. The reflux is a definite improvement over older vitrectomy systems and has practical utility in many of the cases we do.
Dr. Kunimoto: In addition to volume and the force of the reflux being great, I find the system also has the ability to repeatedly reflux without repriming as often as with the Millennium.
Dr. Wald: The Stellaris PC's 5000 cpm rate is great, but we also have the opportunity to work at other speeds such as 4000 or 3000 cpm, which we are not as accustomed to doing. I have not had the system for very long but have been trying different rates. Sometimes I am very happy to progress rapidly along at 3000 cpm. I think we can achieve more efficiency at a lower cutting rate in some situations, not necessarily needing 5000 cpm, which might be most advantageous when cutting close to the retina. We can dial up the rate or dial it down. We have a lot of options, and the speed is easy to change. I had been doing most of my cases with an Accurus at 1500 cpm, so 3000 and even 2000 cpm is still safer and may be faster than the maximal cut rate. Even at 3000 cpm, I am still moving quickly and efficiently with very low vitreous turbulence.
Dr. Heier: I agree. In certain cases, I find the slower cut rate is more efficient. With situations like a vitreous hemorrhage I may work in the 2000 to 3000 cpm range to cut out the majority of it but then when I go back to the periphery, I find I always want to be at 5000.
Dr. Antoszyk: I have migrated toward the 3000 cpm speed and I like the ability to control the aspiration and the cutting at the same time. It is similar to working in 3-D mode with the Constellation Vision System (Alcon), but the Stellaris PC is just as nice because we can essentially have control of the cutting speed as well as aspiration.
Dr. Heier: I use the dual linear mode all the time, which enables me to control both aspiration and cut rate. I used it even before getting the Stellaris PC for cases such as dense membranes and cutting small lens fragments. Now I find it to be even more of an advantage. I am likely to work at a lower cutting rate for the core and then go to the faster rate for the periphery. This way I do not have to worry about modifying it at all.
I will say that I found the control of aspiration to be more of an issue with the older vitrectors. With the newer ones I am less concerned than I was previously about accidentally eating retina with aspiration.
THE ROLE OF DUTY CYCLE IN SAFE AND EFFICIENT VITRECTOMY
Dr. Heier: One of the areas Bausch + Lomb has worked hard in is fluidics. For example, making sure the fluidics are stable as the surgeon moves through a procedure and through different vitreous densities. Does anybody want to comment on their experiences with that?
Dr. Antoszyk: I am always concerned when cutting thick membranes in diabetics and engaging tough tissue that the material may occlude the port and cause a pressure build-up that leads to a sudden rush of fluid into the port when I move the port away. I have not experienced this with the Stellaris PC system. It tends to have an even flow rate. I do not get bouncing of tissue into the cutting tip.
Dr. Heier: What is duty cycle and how does it affect the efficiency of the vitrector?
Dr. Antoszyk: I do not think in practical clinical terms most surgeons are paying attention to duty cycle. However, it is very important in these systems. The duty cycle in the Stellaris is biased toward an open status, which means the cutter is open more than it is closed. The actual closure duration has been shortened. This allows us to cut small pieces of vitreous without building up pressure in the system and without experiencing the bouncing of the tissue. In the Stellaris, the duty cycle is adjusted automatically to optimize cutting. Therefore we can do things like shave diabetic membranes, and as the retina becomes more mobile we are not having the tissue jumping into the port and raising the risk of breaks.
Dr. Wald: I am under the impression that the Stellaris PC will vary the duty cycle depending on the cutting speed. I think the most important part of that is that at a high cut speed it will bias toward an open duty cycle to maximize efficiency. If it were more closed, we would have a much less efficient procedure. I do not think we have the opportunity to alter the duty cycle as the surgeon.
Dr. Blinder: The Stellaris PC has an “optimized duty cycle,” meaning that the software automatically adjusts the duty cycle to maintain the longest open time and still provide a full cut cycle. I think the bottom line is that at 5000 cpm, the system still does not go below 50% duty cycle; and at lower cut rates, the port is open more like 80% of the time. I think that is the secret to the fluidics of the high-speed cutter.
Dr. Kunimoto: Yes, at 2500 cpm, the port is biased open about 75% of the time. At 5000 cpm, it is biased open 50% of the time. So it is never less than 50%.
Dr. Wald: It changes itself. It is built into the machine to change depending on the cut speed. With Alcon's Constellation system, the surgeon has to manually change the duty cycle. The Stellaris is programmed to maximize the efficiency of the cutting speed.
Dr. Heier: I think the strength of the Stellaris PC in this area is that it maintains the ideal duty cycle and it is something the surgeon does not need to think about. Certainly this is an important point for differentiating it from previous technologies and other machines.
INNOVATIVE HANDPIECE FEATURES
Dr. Heier: The handpiece of the Stellaris PC is different from other machines as well. The cutting port is closer to the end. Is this something any of you have noticed or appreciated?
Dr. Tewari: The grip itself is nice, but having the port really close to the tip is wonderful. With diabetic dissections, the majority of the case can be completed with the cutter alone. Only rarely do you need to use intraocular micro-scissors. Also with the 5000 cpm rate and having the port so close to the tip, we have a great deal of stability while working around posterior hyaloid and fibrous traction on the retina. Less instrumentation needs and greater control leads to a more efficient surgery and likely less iatrogenic complications, such as retinal breaks and hemorrhage.
Dr. Blinder: Yes, having the port closer to the end minimizes the use of scissors. I like the innovation of the rubber grip, too. When any fluid comes in contact with other hand pieces, they become very slippery and difficult to manipulate. Even when the Stellaris PC hand piece is wet, I can still grip it well due to the new rubber grip.
I also like the tactile port locator. It allows me to locate the open port when I am having difficulty actually viewing it.
Dr. Heier: I have found the 5000 cpm rate combined with the port closer to the end to be almost like having a small scissors. I am able to dissect membranes with the cutter rather than going in with scissors or certain types of blunt dissection to separate membranes. I can come up comfortably almost flat against retina and use the cutter to dissect these tissues almost as well as I was able to with other techniques.
Dr. Antoszyk: I agree with Dr. Heier that the new technology in the Stellaris PC, as well as other high-speed cutting systems, has obviated the need for automated scissors. Because of this, Bausch + Lomb has not included an automated scissor driver feature on the unit. I haven't used automated scissors in more than 2 years. With the new cutter, I can get down to the surface, dissect the membranes and use manual vertical scissors if the need arises.
Dr. Blinder: I have not used automated scissors in years either. I do not see the need. The 5000 cuts per minute should really make them obsolete.
Dr. Kunimoto: In addition to everything said, another significant innovation of the pneumatic hand piece is how lightweight it is compared with the Millennium's electric high-speed cutter.
USING THE STELLARIS PC IN A VARIETY OF CASES
Dr. Heier: Have you used the Stellaris PC in other types of cases and found it to be different than machines that were cutting at 2000 or 2500 cpm? Is it just as effective for dissecting membranes in proliferative vitreoretinopathy (PVR) cases as it is in diabetic cases?
Dr. Antoszyk: Fortunately, PVR is a rare entity and the severity of cases we are seeing these days is much less. However, I can anticipate that in severe cases with anterior loop traction, the small-gauge, high-speed cutter on the Stellaris PC, with its port closer to the tip, would be advantageous in opening a trough.
Dr. Heier: I see a number of PVR referrals. I find that the control at the 5000 cpm rate is really nice for handling these cases.
Has anyone used the Stellaris PC to deal with a dropped lens? How is the flow through the vitrector?
Dr. Kunimoto: I have done several cases with the fragmatome, and I would say this is one area in which I do not notice a big improvement from the Millennium to the Stellaris PC. I also use dual linear for removing nucleus, and I use the pulse for more efficient lens removal. I find that lowering the ultrasound power helps to minimize chatter, so the lens does not shoot off the tip.
Dr. Heier: I have used the Stellaris PC for removing cortical material and smaller lens fragments, and it does a nice job, although I certainly decrease the cutting rate. I have not had the opportunity to use the system with the fragmatome, but I have always done my fragmentations with dual linear, including with the Millennium. It provides better control so if I need to be at low power to prevent the fragments from blowing off the tip, I can do that. When I am faced with really hard lenses, I often block the fragmatome at one end with my light pipe and aspirate harder. Also, from what I understand the Stellaris PC offers the same modality that is used on the Constellation and Accurus, proportional vacuum to occlude the lens followed by proportional power to emulsify with out blowing of the tip.
Dr. Wald: I agree that with the Millennium, it is best to use dual linear, which did not seem to be as necessary with the Accurus. I have done hundreds of cases with the Accurus in that manner. The dual linear approach works very well on the Millennium and the Stellaris PC. It seems I have been able to use a lower phaco power with the Stellaris than with the Millenium or Accurus.
Dr. Heier: Have you done any cases with the Stellaris PC that you think were more difficult than with the Millennium or the Accurus?
Dr. Antoszyk: No.
Dr. Blinder: One minor setback with the Stellaris PC compared with the Millennium is not having the laser integrated into the machine but Bausch & Lomb has assured us that we will have a way to integrate this in the future to give the surgeon full control of the laser.
Dr. Wald: I think compared with the Millennium, it takes a slight bit of getting used to the Stellaris PC foot pedal. You have to be a little more precise to activate it. It was somewhat more forgiving with the Millennium. However, I have gotten used to it and it has not been a big deal.
Dr. Tewari: I agree about the foot pedal. The ergonomics have improved with some of the foot pedal buttons and you do need to push a little harder to get them to engage, compared to the Millenium.
UNPRECEDENTED VERSATILITY IN ILLUMINATION
Dr. Heier: Have you experimented with the different light sources and filters on the Stellaris PC?
Dr. Antoszyk: The green light enhances the tissue contrast, particularly during peeling of the internal limiting membrane. Also, when dyes are being used, the depth of field and clarity of the tissue planes is enhanced. During fluid/gas exchange, the amber light decreases glare markedly, especially with use of a widefield viewing system. These have been the aspects I have found to be most helpful during vitrectomies.
Dr. Wald: Do most people use the mild blue filtering effect—it is like a yellowish light—for most cases?
Dr. Heier: Do you mean the amber one?
Dr. Wald: Well, one of the options is a bright amber, which I did not like. I have done most of my cases with the option that seems to be a more gentle amber, as if I were wearing light sunglasses.
Dr. Antoszyk: That sounds like the yellow filter.
Dr. Wald: It is yellow, but not too yellow. It seems to me it filters out some of the blue light and is very comfortable. I have not used all the options enough to determine which would be helpful in different circumstances, but I am exploring the issue. The important aspect is that surgeons can find a light source and color that they feel is most helpful to accomplish specific surgical goals.
Dr. Antoszyk: The yellow light has the blue filter in it, so if we need to substantially increase the brightness, it increases the safety profile.
Dr. Tewari: I like to use the green filter, especially with triamcinolone assisted membrane peels. Another helpful feature is having two illumination lamps. One is standard xenon, and the other is mercury vapor. Surgeons who are more accustomed to using the Photon II (Synergetics) mercury vapor lighting can use this built-in light. Having that flexibility is a nice touch.
Dr. Blinder: The Stellaris PC also allows dual independent lamp function. So if we want to use a chandelier system and a light pipe, we can. Also, we can use the second light source as a backup. All of us have had our main light source go out and had to deal with the interruption of getting a different machine or change the light during the case.
Dr. Kunimoto: Yes, the diversity of lighting options affords every surgeon his or her preferences. It is a very nice feature.
Dr. Heier: Have any of you had the pop-up box come on for reaching the higher lumens on the machine?
Dr. Kunimoto: How high do you have to go to prompt that? I thought the brightness was quite good. I have been at 40% but have not gone above 50%, because of the adequacy of the light source.
Dr. Heier: If I am not mistaken, the default is 40% and once you reach 68%, the pop-up box appears, indicating that you are at a level that could be damaging to the retina based on a calculation considering 15mm distance from the tip of the light probe to the retina. It seems as if some surgeons are concerned this means we have decreased safety with this light source, but it is actually quite the opposite. We can set the system at the default level, and if the need arises to go above that, perhaps because we are using light from an angle or from a wider view, we have that capability. It is just like when we increase the intraocular pressure and get the warning telling us we are at a level above what is normally used so just be careful. As far as the Stellaris PC lighting, I would not expect many of us are going to employ lumens high enough to prompt the pop-up box.
Dr. Blinder: Being alerted as we approach higher lumens is at least a good reminder that the potential for light toxicity exists. The odds of ever getting to that level are minimal, but it is a nice safety feature.
Dr. Antoszyk: It is also just as important to remember that potential light toxicity depends upon time of exposure and the proximity of the tip to the retinal surface. We can hold the tip, especially with the brighter lights, much farther away, up close to the cannula tip, thereby decreasing the risk of creating a phototoxic lesion. RP
Retinal Physician, Issue: March 2011