Several years ago, I was fortunate to be part of a team of surgeons who were asked by Bausch + Lomb (Aliso Viejo, CA) to work on the next generation vitrectomy system to replace the Millennium. The engineers asked us to devise a wish list of features for the new machine and in turn, our team produced a relatively long list, which included some practical items (eg, faster cutter) and some not-so-practical items (eg, mp3 player). After time and discussion, however, we agreed that because Bausch + Lomb is a global company that serves surgeons from a variety of regions and economies, the best machine to build would not be over-engineered or overly expensive, but would be an elegant, state-of-the-art system focused primarily on improving patient outcomes and safety. The result of these early discussions and subsequent developments is the Stellaris PC.
The next-generation technology that is included on the Stellaris PC includes an ultra–high-speed vitreous cutter, a brighter and safer light source, a user-friendly interface, and an open architecture. The open architecture is an exciting feature because with this design, the surgeon is able to use disposable instrumentation made by other manufacturers. Not only does this give the surgeon more choices, but it also puts pressure back on Bausch + Lomb to design disposables that surgeons will want to use with the Stellaris PC. The Stellaris PC is the only microincision dual-function platform available. The advanced technology allows for an easy transition between microincision cataract surgery (MICS) and transconjunctival sutureless vitrectomy (TSV).
The cutter on the Stellaris PC can operate at speeds as high as 5000 cuts per minute (cpm). The ergonomics of the cutter are excellent. The microvit-style handle is made of a lightweight plastic that is color-coded for gauge size and has an optional extension feature for those surgeons who prefer a longer handle. The handle also has a tactile port indicator.
For many years I used the electric Lightning high-speed cutter (Bausch + Lomb). I was comfortable with the size and weight of that handle, but there were many surgeons who were dissatisfied with the design, so many will welcome the more traditional size and shape of the Stellaris PC cutter.
High-speed 5000 cpm vitrectomy is currently state-of-the-art, and the ability to achieve this with a pneumatic cutter is a significant advantage. The geometries of the commercially available cutters are shown in Table 1.
Note that the Stellaris PC and the Constellation cutters’ ports are both 0.0097 inches from the tips of the cutters, which is important because a closer proximity of port to tip allows the surgeon to work more closely to the retinal surface.
Also shown in Table 1 is that the port area on the Stellaris PC
is larger than that on the Constellation (0.328
mm2 vs 0.313
mm2). In my opinion, this larger port area is an advantage because it allows vitreous to be removed more efficiently.
Previous-generation Cutters and Flow
Approximately 10 years ago, I performed some studies on flow comparing the 25-gauge Bausch + Lomb electric cutter and the Alcon pneumatic cutters. When high-speed cutting was first introduced by Bausch + Lomb, we observed that the electric cutter achieved maximum flow at its maximum cut rate, which was opposite to what we had been taught in our surgical training. The traditional pneumatic cutter achieved maximum flow at the minimum cut rate, with the cutter taking bigger bites of vitreous, which was consistent with the traditional teaching. We found, however, that at maximum cut rates, the electric cutter actually achieved 50% greater flow than the pneumatic cutter at the same maximum cut rate. This higher flow allowed for effective 25-gauge surgery using an electric cutter.
A traditional pneumatic cutter is closed by a pulse of air and opened by a spring. The spring’s mechanical properties are fixed and therefore always open the cutter at the same velocity. The electric cutter is driven back and forth by a gear mechanism and is actively closed and actively opened, similar to a sewing machine needle.
The faster the cutter closes, the faster it opens, allowing the port to remain open approximately 50% of the time, independent of cut rate.
At lower cut rates with the earlier-generation pneumatic cutter, a pulse of air closes the cutter and the spring opens it; the cutter pauses while it is waiting for the next pulse of air, and during that time, the port is open. High flow results because the port is open for a disproportionately larger amount of time. If one were to attempt to use an extremely high cut rate in this model, the pulse of air would close the cutter and the spring would begin to open it, but before the cutter could open, the next pulse of air would arrive to close it. As a result, the port is open for a small percentage of the duty cycle. Conversely, the electric cutter is driven in a sinusoidal pattern where it is open 50% of the time (a 50% duty cycle).
To compensate for the fact that their earlier-generation pneumatic cutter could achieve higher effective flow only at low cut rates, Alcon developed what was termed “3D”, Dual Dynamic Drive. In 3D mode, as vacuum increased, the cut rate automatically decreased, allowing effective core vitrectomy flow, but with increased vitreous traction.
New Generation Pneumatic Cutters
The Stellaris PC incorporates a next-generation pneumatic cutter with the advantages of the familiar lightweight microvit-style handpiece. With an optimized duty cycle, the port is open at least 50% of the time, even at 5000 cpm. Thus, we are able to employ ultrafast cut rates but with a duty cycle that allows for effective vitreous removal at the highest cut rates.
Poiseuille’s Law is commonly involved in discussions of flow during vitrectomy. It describes, however, the behavior of ideal, homogenous fluids during laminar flow—in my opinion it does not accurately describe the behavior of vitreous. Vitreous is a complex viscous mixture, which may also contain bits of blood and tissue, and does not behave at all like an ideal fluid. Thus, at low cut rates, larger pieces of vitreous create resistance to flow as they travel down the lumen of the tubing. As cut rate increases, the pieces of vitreous are smaller and behave more like liquid.
Essentially, the mechanical properties of what is moving up the tubing changes at higher cut rates. The 23- and 25-gauge cutters at 5000 cpm on the Stellaris PC produce vitreous flow that approaches that of a 20-gauge cutter. Using the lightweight pneumatic cutter and 5000 cpm with an optimized duty cycle allows surgeons to control flow simply and intuitively by varying vacuum with the footpedal.
Vacuum and Fluidics
The vacuum on the Stellaris PC is controlled by an advanced algorithm that produces accurate, smooth, and linear aspiration that is accurate and predictable at low-end vacuum (as low as 2 mm Hg). Vacuum is robust and responsive—the Stellaris PC can achieve 0 mm Hg to 600 mm Hg in 1.5 seconds and dual vacuum lines can be switched on demand by the surgeon, putting more control into his or her hands.
The Stellaris PC uses either gravity or vented Air Forced Infusion (AFI), both of which produce stable, predictable fluidics. The pressurized bottle is more responsive than an automated IV pole, allowing a surgeon to go from elevated infusion (60 mm Hg) to standard pressure (40 mm Hg) in approximately 0.5 seconds and the rise and fall times follow a linear path.
The pump is independent and does not rely on wall air. Stellaris PC also has a power failure mode that maintains existing intraocular pressure (IOP). It does not, however, have any automated IOP control feature or measuring system. In my opinion, estimating IOP can be dangerously inaccurate—the only way to accurately measure real-time IOP is with a pressure transducer in the eye.
Clinical Experience With Cutting
Our colleagues in Europe had access to Stellaris PC several months before those of us in the United States and the feedback has been excellent. Stanislao Rizzo, MD, has commented that the position of the port in all three gauges of the cutter offer exceptional quality in cutting and fluidics.
The core vitreous can be removed quickly and the surgeon can work adjacent to the peripheral and detached retina with little retinal movement at 5000 cpm.
Trocar/Cannula Entry System
The Stellaris PC has a new 23-gauge trocar/cannula Entry Site Alignment (ESA) design with a sharper blade that allows for outstanding wound architecture with less insertion force.
The ESA design continues to employ a polyamide cannula, which maintains better retention in the incision than a stainless steel cannula. The cannula is slightly beveled, making entry into the eye even easier.
The illumination on the Stellaris PC is also highly advanced. First, the machine has a dual light source with both xenon and mercury vapor. Additionally, Stellaris PC has integrated color filters with amber, yellow, and green
filters that are switchable with the surgeon-controlled footpedal. The xenon light source is “whiter” than mercury vapor with a cut-off filter of 435 nm and is familiar to most surgeons. For longer surgical procedures, the mercury vapor light is ideal to decrease the risk of prolonged exposure and phototoxicity.
We can alter the phototoxic hazards of light, however, using a filter. In terms of reducing phototoxicity, the amber filter is the most effective, with 118% more safety margin, the yellow filter is next with 16% more safety, and the green filter has the least effect at 10% increased safety.
Currently, there are no rules to guide us in the selection of color filters during vitreous surgery. However, many surgeons report that certain colors seem to enhance their ability to identify ocular structures during surgery. For example, some surgeons report that they can see the vitreous better under yellow light, while others report better visualization of membranes under green light. Also, research demonstrates that individual responses to light will vary greatly due to factors such as surgeon age and patient lens opacity.Functionality and Versatility
The Stellaris PC is a compact and staff-friendly machine. The footpedal is wireless, which is greatly appreciated by my staff – one less cable to drag along the floor! I like the footpedal, as well, particularly because Stellaris PC allows me to use it for Dual-Linear control, meaning that I can independently vary vacuum and cut rate (or phaco power). It is particularly helpful when I am chasing after dropped lens fragments—I can engage the lens material, increase vacuum and then slowly increase frag power to consume the fragment without shooting it off the end of the port. It truly is an advantage to have the ability to control these and a multitude of other functions with the programmable wireless footpedal, which can store multiple surgeon settings.
The Stellaris PC screen interface is user friendly and does not have layers of menus to navigate. All parameters that require control during vitrectomy, cataract surgery, or combined cataract-vitrectomy are on one screen. Additionally, the screen is light adapting and it swivels, making it easy for the staff or surgeon to move it either toward them or away from them.
The Stellaris PC has many features that make setup easier for staff such as hands-free automatic priming, which frees the nurse or surgical scrub tech to attend to other tasks while Stellaris primes the cutter and the tubing.
The first week that the Stellaris PC was approved in the United States I had the opportunity to use it in my OR. My first 25-gauge case using this system was fairly straightforward and demonstrates its utility and functionality.
The patient was a younger monocular woman who with proliferative diabetic retinopathy and a tractional retinal detachment involving the temporal region of her macula. I prefer to use chandelier lighting for diabetic vitrectomy, Chandelier lighting used for a diabetic vitrectomy, and with the Stellaris PC’s open architecture, I am able to use third-party disposables. I used the cutter at 5000 cpm to reduce traction and the risk of retinal tear. At this cut rate, I can shave the scar tissue from the retinal surface safely. The Stellaris PC has a reflux function that can effectively blow blood away from the retinal surface. In this case, no diathermy was needed.
The traction detachment involved an area of very thin and atrophic retina, so I chose to operate bimanually. With the chandelier in the mercury-vapor light source, I used a serrated pick in one hand and the cutter in the other. This allowed me to provide slight counter traction to safely dissect the fairly thick membrane from the atrophic retina. I find that being able to shield the retina a little bit with the pick is helpful, and the Stellaris PC cutter eliminates the need for scissors. I did not induce any retinal breaks, but because of the traction, I applied laser and performed a fluid/air exchange at the end of the
case. The patient’s eye was a bit soft after I removed the cannulas, so I had injected a small bubble of filtered air with a 30-gauge needle. If I feel that the eye is maintaining pressure well, I do not suture. If, however, a leak persists, I will open up the conjunctiva and suture. In this case, the eye maintained pressure nicely and, indeed, her IOP was 18 mm Hg the day after surgery and the eye has done quite will since the operation.
Since 2007, anterior segment surgeons have had access to the Stellaris, which has been considered a premier microincision cataract platform. The Stellaris PC merges the functions of cataract surgery with a vitrectomy system. In subsequent articles within this supplement to Retina Today, Boris Malyugin, MD, discusses his use of the Stellaris PC for 1.8-mm MICS and Roberto Bellucci, MD, discusses the use of Stellaris PC for combined anterior and posterior segment procedures.
Carl C. Awh, MD, practices at Tennessee Retina in Nashville, TN. Dr. Awh states that he is a paid consultant to Synergetics, and a paid consultant to Bausch + Lomb. He may be reached at +1 615 983 6000; or via e-mail at firstname.lastname@example.org .