Get Behind the Wheel of the Constellation
Knowing the bells and whistles of a particular vitrectomy platform widens surgical potential and increases confidence and safety.
I recently completed a vitreoretinal surgery fellowship at Wills Eye Hospital in Philadelphia, Pa., where I had the privilege to operate 5 days a week over the past year with 15 talented vitreoretinal surgery attendings. Never again will I get the chance to perform 1200 surgical cases in 1 year and gain surgical proficiency so exponentially. The lessons, techniques, and skills learned have been indispensible to my career. Much like my car, I got behind the wheel of the Constellation Vision System (Alcon) for 8 to 10 hours each day, getting to know the ins and outs of the machine.
An often-overlooked feature of the Constellation is the machine’s user-friendly interface (Figure). The Constellation’s easy-to-read screen allows surgeons to choose among the device’s various functions and clearly indicates when the user has switched from, for example, core vitrectomy to shave vitrectomy. Although retina surgeons often first consider the technical aspects of the device (such as those detailed below) the most important functions, such as the clarity an interface provides cannot be ignored.
Intraocular Pressure Control
Intraocular pressure (IOP) control is one feature that sets the Constellation apart from other vitrectomy machines. This control allows surgeons to keep IOP within 2 mm Hg of a preset level. Unlike older platforms, the Constellation, combined with valved trocars, becomes a controlled, predictable system. The IOP control utilizes flow sensors at the bottom of the cassette that directly compensate to maintain a set pressure. Predictable IOP is paramount in cases involving patients with diabetic tractional membranes, in which high IOPs are often intermittently required for hemostasis. IOP control is also important in patients with glaucoma, as such control ensures safe operating pressures to minimize damage to the optic nerve.
Additionally, cases involving perfluorocarbon liquid (PFCL) are predictable when performed with the Constellation and valved cannulas, as this configuration minimizes dispersion of small PFCL droplets and reduces the risk of PFCL entering the subretinal space.
When performing vitrectomy with high aspiration, surgeons rarely outrun the infusion. However, there are situations where infusion issues can occur.
Spatial factors play a role in IOP control: The patient’s eye level must be at the same height as the bottom row of connectors on the cassette. If the patient is lower than those connectors, increases in IOP will occur. IOP increases at a rate of approximately 1.87 mm Hg for every inch the patient’s eye is below the cassette connectors, and such unevenness results in decreased aspiration by the same factor. For example, if you have IOP settings for 25 mm Hg and the patient’s eye level is 10 inches below the cassette, the eye’s actual IOP will be 43.7 mm Hg (25 + 18.7 = 43.7). To correct for the desired level of the patient’s head during surgery, the Constellation has a patient eye level setting, allowing the surgeon to make this adjustment so that the pressure he or she sets is the actual pressure in the eye.
Prior to unclamping the infusion, direct visualization of the infusion cannula in the vitreous cavity is critical to prevent complications, including infusion under the retina or in the suprachoroidal space. In cases that preclude direct visualization, 6-mm trocars may be beneficial. Inadvertent infusion into the suprachoroidal space is not a good way to start the case, and air infusion into the choroid could result in fatality due to air embolism.
Infusion issues can also develop if the infusion cannula is directed anteriorly behind the lens. This issue can be avoided by taping the infusion line to maintain the infusion’s angle toward the posterior pole. If the infusion is correctly positioned and IOP stability remains an issue, clearing vitreous from the infusion cannula area usually resolves these problems.
Another key advantage of using the Constellation is the dual pneumatic vitreous cutter, which relies on independent airflow to drive closing and opening of the cutter itself. Improved design with the Constellation includes optimized port location placed closer to the tip, allowing improved dissection of preretinal membranes, which proves particularly helpful in cases of tractional retinal detachment (TRD) secondary to proliferative diabetic retinopathy.
Thanks to the dual pneumatic system, vitreous cutters offer superior cutting forces and cut rates up to 7500 cpm without affecting efficiency and port flow; compared with older vitrector models, in which increased cut rates came at the expense of port flow, this is a massive improvement. Flow through the port is maintained despite higher cut rates, thus decreasing the cone of influence on the vitreous, resulting in less traction when working close to the retina.
Duty cycle, which is the amount of time the port is open during the cutting cycle, can be controlled by the surgeon independent of the aspiration and cut rate. The three settings available are core (port biased open), 50/50, and shave (port biased closed). An additional setting is called momentary, which allows footpedal–controlled aspiration with side pedal–controlled cutting at low cut rates. The momentary setting is ideal for removing lens fragments that do not require the fragmatome.
The cutting settings can be quickly changed during a case with footpedal control, thus allowing enhanced surgeon control for all situations encountered. Shave vitrectomy works well over detached retina, often cutting vitreous with little underlying movement of the retina. These features are available in 23-, 25-, and 27-gauge cutters. All gauges have a full complement of surgical adjuncts including forceps (eg, max grip, internal limiting membrane), soft-tip extrusion tips, and lasers. As a result, there is a full armamentarium available to accommodate to the surgeon’s preferences.
Of utmost importance during vitrectomy surgery is proper lighting to illuminate vitreous and visualize membranes during peeling. However, light toxicity and retinal damage are concerns. The Constellation uses a xenon light source that has a radio frequency identification (RFID) probe that automatically regulates light intensity based on the probe gauge size, thus minimizing the likelihood of inadvertent light toxicity. The RFID also allows easy connection of chandeliers and lighted lasers that can be individually selected and controlled on the platform without needing to unplug other lights.
Auto Air-Fluid Switch, Integrated Gas Fill, and Integrated Laser
Use of air and gas with the Constellation is straightforward. The surgeon has automatic air-fluid switch control with the footpedal, allowing seamless transition from fluid to air. The IOP control continues to function, maintaining a closed, stable system under air much the same as under fluid. The vitrectomy platform also has an integrated gas fill for SF6 and C3F8. The machine automatically purges the gas to ensure pure gas, and the surgeon or scrub technician then dilutes to the desired gas concentration. This feature allows fully integrated gas fill without the need for the circulator to assist in pulling the gas.
Continuing the integrated concept, the Constellation also contains a laser, which can be selected with the main footpedal, as part of the platform. A separate laser pedal allows surgeon control of changing the power up or down and enabling and disabling the laser. The options for lasers include straight and curved, illuminated and nonilluminated. A significant benefit of the curved illuminated laser is the ability for surgeon-independent scleral depression with simultaneous laser for peripheral retinal breaks, even in phakic patients across the eye. During retinal detachment repairs (Video; eyetube.net/v.asp?f=enome), the curved illuminated laser allows the surgeon to adequately treat all breaks, including the anterior portions of a tear.
I already alluded to the importance of valved cannulas combined with the advanced IOP control in the Constellation platform. Additional features of the EdgePlus trocars include advanced blade design to create linear wounds. The trocar cannulas also easily detach from the blade after insertion, often eliminating the need to use a second instrument to hold the trocar cannulas, instead allowing the second hand instrument to stabilize the eye. The cannula design also enhances instrument rigidity and ease of instrument movement within the cannula. The hubs are low profile, and the valves allow easy access to instruments. Wound construction is paramount for creating a self-sealing wound and should include conjunctival displacement and a beveled approach at approximately 30°.
Viscous Fluid Injection
The Constellation has a viscous fluid injection setting to allow the insertion and removal of silicone oil. The silicone oil cannula attaches to the vitrectomy platform, and the settings allow controlled extrusion (up to 650 mm Hg aspiration) and infusion (up to 80 mm Hg). Silicone oil infusion is a crucial step in many diabetic TRD and proliferative vitreoretinopathy cases. Of key importance is venting the air at the highest point to ensure that all air is removed prior to topping off the silicone oil. In pseudophakic patients, the soft tip with active extrusion can aid in removing the final air in the anterior vitreous cavity
Removal of silicone oil is also easily performed with the Constellation with the same cannula. Silicone oil (1000 cs) can be removed with the 23-gauge or 25-gauge system quickly, with longer times needed to remove higher viscosity silicone oil (5000 cs). Insertion is even faster, usually taking less than 3 minutes. A key step to ensure removal of all silicone oil is to perform two or three air-fluid exchanges while keeping the vitreous cutter on aspiration-only with the port facing down at the air-fluid interface. You will see the “oil slick” on the surface, and this will aid in determining the presence of any retained silicone oil and need for further rinses. Retained oil in the capsular bag or anterior chamber will require further steps such as anterior chamber washout, but the above technique will be beneficial.
The viscous fluid injection cannula and tubing can also be used to perform subretinal tissue plasminogen activator (tPA) injection in cases of massive subretinal hemorrhage or submacular hemorrhage. The tPA can be placed in the viscous fluid cannula with the attachment of a 41-gauge subretinal tip. The infusion settings should be adjusted to between 8 mm Hg and 14 mm Hg, or until the tPA has a fast drip out of the 41-gauge instrument. This allows controlled infusion of subretinal tPA without the dependence on an assistant manually pushing a syringe with unknown infusion pressure.
Fundamental aspects of the Constellation vitrectomy platform are its ease of use and efficiency. With the RFID plugs, the correct settings are automatically populated when each instrument is plugged in. As a result, setup is straightforward and can be performed by the scrub technician or surgeon. The circulator needs only to spike the bottle, select the doctor, and press the prime button. This frees him or her to perform other tasks and speeds room turnover, allowing for shorter time between cases and overall improved efficiency.
When we buy expensive electronics or a car, customer service and support are key features that result in overall satisfaction with the product. The Constellation provides nothing short of excellence in this department. The surgical representatives are valuable sources of information new and seasoned vitreoretinal surgeons. For everything from initial demos and programmed settings to real-time troubleshooting, the company’s representatives reliably serve surgeons using their platform. I can think of several instances when I had a question before, during, or after a case and I could count on our regional surgical representative to answer a call on the weekend to walk step-by-step through the issue.
I liken using the Constellation to driving my favorite car: I love getting behind the wheel. The platform is compact and efficient, providing an all-in-one machine. The dual pneumatic cutter allows cut rates as high as 7500 cpm and independent duty cycle control, thus providing the utmost safety and efficiency. As a surgeon, I have full control during surgery and can easily switch between settings with clicks on the footpedal. Futhermore, everything has voice confirmation, so, with every setting change, a pleasant voice confirms my actions. I know the Constellation will serve me well and get me to 250 000 miles—just like my first car. n
S. K. Steven Houston III, MD, is a vitreoretinal surgeon with Florida Retina Institute in Central Florida (Orlando area) and North Florida (Jacksonville area). He has no relevant financial disclosures. Dr. Houston may be followed on Twitter at @trieyedoc and reached at email@example.com.