Bimanual phaco is an evolving technique. Those who have tried it are debating its advantages, its disadvantages, and its future. Although the technique was originally proposed more than 20 years ago, new cold phaco technologies such as laser phacoemulsification and WhiteStar (Advanced Medical Optics, Inc., Santa Ana, CA) have led to renewed interest. Here, top surgeons give their opinions on some of the most commonly asked questions regarding bimanual phaco.
1. WHAT ARE THE ADVANTAGES OF BIMANUAL PHACO USING ULTRASOUND?
Dr. Chang: Although promising, bimanual phaco is presently a technique in search of a definitive indication. Over recent years, many innovators have sought to advance the techniques and technology that will allow us to remove a cataract through a 1.0-mm incision. In my opinion, the “micro phaco” system using the WhiteStar cold phaco technology that Randall Olson, MD, of Salt Lake City developed is the best bimanual procedure to come along so far. Rather than having to purchase nonultrasound technology, this is an upgrade to a conventional phaco machine (the Sovereign System, Advanced Medical Optics) that allows us to remove even brunescent lenses with a bare 20-gauge phaco tip. As everyone knows, laser phaco is ineffective for a dense nucleus, and WhiteStar also circumvents the chatter and turbulence that is normally present with brunescent fragments and a micro phaco tip. Thus, WhiteStar ultrasound is currently superior to laser for this application, in my opinion.
Dr. Gravlee: The point of the bimanual technique is that, because it does not use heat-generating ultrasound, the phaco tip may be used without an irrigating sleeve (Figure 1). Bimanual phaco may increase a surgeon's access to nuclear material. The angle of attack can be steepened with a shorter tunnel, and a narrower tunnel is less likely to leak postoperatively and can therefore be shorter and still self-seal. Also, a shorter tunnel undergoes less distortion, reducing the dimple-down effect of the cornea and providing better visibility. There is no steal effect of the BSS (Alcon Laboratories, Inc., Fort Worth, TX), so there is a stronger current of cataractous material to the tip of the extraction probe.
Using a sleeveless phaco probe also offers the advantage of decreased hydration of the corneal stroma surrounding the tunnel incision. A sleeved probe has two irrigating holes in its side that allow BSS to flow tangentially from the probe and directly hydrate the corneal tunnel incision stroma. The secondary whitening of the stroma can obstruct the view of the surgeon intraoperatively, and postoperatively the patient may complain of peripheral blurring. A sleeveless probe obviously reduces corneal stromal hydration. Also, hydration spreading from a wound 1.5 mm or smaller is not as noticeable as from a wound 2.5 mm or larger. Additionally, the newer lollipopping and chopping techniques require the sleeve to be pulled back farther on the probe, thus enhancing hydration from the irrigating holes.
Dr. Fishkind: Bimanual phaco is made possible by the advent of cold phaco, which was developed as part of the WhiteStar technology. Cold phaco involves extremely short pulses of power on and power off, which allow cooling of the phaco tip. The cold phaco tip can enter through a tiny incision without burning the cornea. The advantages of bimanual phaco are: (1) its “cold” energy source cannot cause wound burn, and (2) the incisions are extremely small and therefore should be astigmatically neutral. Bimanual phaco incisions should seal more tightly, reducing the chance of leakage and postoperative complications such as flat chambers or endophthalmitis. The small incisions should increase the efficiency of phaco by changing the movement of the currents within the anterior chamber so that the separated irrigation pushes material toward the sleeveless phaco tip. The lack of a sleeve also draws material toward the phaco tip. Increasing the effectiveness of phaco reduces the power delivered to the anterior segment, which translates to faster recoveries, less corneal edema, and less endothelial cell loss. It is important to note that studies are still underway to determine whether this improved efficiency actually exists with bimanual phaco.
2. DOES INCISION SIZE MATTER IN TERMS OF FINAL VISUAL OUTCOMES? IF SO, BY HOW MUCH?
Dr. Chang: For a temporal clear corneal approach, sub-3.0-mm incisions are safe, astigmatically neutral, and currently attainable for silicone and hydrophobic acrylic IOLs. It is not intuitively obvious that smaller incisions will be better, and clinical studies must decide this issue.
Dr. Gravlee: Incision size has a direct effect on patient satisfaction, postoperative comfort, wound integrity and safety, endothelial cell loss, postoperative corneal clarity, and reflux of ocular surface debris into the eye that causes endophthalmitis. My guiding principal has always been to use a square tunnel incision to create a better seal and help prevent endophthalmitis. Square tunnels are not very practical with incisions larger than 2.5 mm, and I believe larger, nonsquare incisions raise the endophthalmitis rate accordingly. Surgeons are well aware of the disadvantages of using sutures to secure larger wounds. Pushing the envelope with newfound small-incision capabilities will influence the IOL companies to deliver FDA-approved lenses that can be implanted through 1.5 X 1.5 mm square incisions for 19-gauge extraction probes (even smaller incisions are possible with smaller-gauged probes).
The incisions used in bimanual phaco are quite stable. Additionally, because the technique involves two incisions that are theoretically interchangeable, it is possible to obtain a better approach angle with which to access objects within the eye by swapping instruments between the incisions.
Dr. Fishkind: We know that incision size matters, because multiple investigators have shown that smaller incisions create less astigmatism, and less astigmatism translates to improved visual outcomes, especially if we couple the cataract surgery with astigmatic surgery.1 Without a method that guards against inducing cylinder, we cannot treat it prospectively or effectively. Additionally, as Dr. Olson proved, incisions larger than 3.0 mm have an increased need for sutures. We want to avoid using sutures, because they can induce astigmatism and also must be removed.
3. WHAT IS THE GAUGE OF THE INSTRUMENT, AND DOES INFLOW CAPACITY DICTATE THE INCISION SIZE NEEDED?
Dr. Gravlee: Fluidics is the big problem. Ingress must equal egress to prevent the corneal dome from collapsing and the intraocular contents from trampolining. Amar Agarwal, MD, of Chennai, India, solves this problem by using an aquarium pump to generate a power fluid infusion. The risk of litigation has prevented me from attempting this in the US.
Wounds must be tight in order to prevent intraoperative leakage. Therefore, extraction probes, irrigating choppers, bimanual I/A instruments, and even vitrectomy probes must all be standardized to the same gauge on each individual case so that all the instruments can enter through both wounds, yet fit tightly to minimize leakage.
Dr. Fishkind: Inflow capacity does not dictate incision size; rather, the size of the equipment dictates the size of the incision. The equipment should be the smallest gauge possible to fit through the incision and maintain a watertight seal. Unlike a sleeved phaco tip, for example, with which there is a controlled egress of fluid at all times, a bimanual phaco incision tightly controls both the fluid ingress and egress—they allow no leakage. To achieve a 1.4-mm incision, we use a 20-gauge MVR blade (Alcon Laboratories, Inc.) and a 20-gauge phaco tip. That incision size allows us to insert a 1.4-mm irrigating chopper in one incision and the bare phaco tip through the other. The corollary to this question is, how small can the incision size for infusion and instrumentation be to maintain adequate inflow? We are beginning to experience problems with inflow with bimanual phaco. These 20-gauge incisions and irrigating instruments are just adequate to provide enough inflow to create sufficient anterior chambers.
We are trying to improve bimanual phaco irrigating instruments. For instance, we now raise the bottle height with extenders to improve inflow. We have also been trying to improve the orifices of the irrigating chopper so that it will allow a better flow of fluid. There are structural issues in terms of the size of the lumen that can be produced in a tube before the tube loses rigidity and collapses. We are beginning to reach such limits with our current instrumentation and are exploring different materials and designs. Some researchers have proposed using pressurized inflow, a concept we are also examining.
Surgeons may have difficulty making the capsulorhexis in bimanual phaco if they use forceps. A standard capsulorhexis forceps will not pass through a 1.4-mm incision, so we must use a coaxial capsulorhexis forceps. I am currently using a model developed by Duckworth & Kent Ltd. (Baldock, Hertfordshire, England) (Figure 2) . They also manufacture a Nagahara-style coaxial chopper with two sideport infusers that seem to maintain the chamber effectively.
4. IS THERE A LEARNING CURVE WHEN TRANSITIONING TO BIMANUAL PHACO?
Dr. Chang: There is certainly a learning curve when switching to bimanual phaco chop, during which the nondominant hand holds the chopper and carries out most of the work. The increased diameter of the irrigating chopper somewhat limits the mobility of the instrument, and the user must avoid retracting the chopper so far that the irrigation port slides out of the anterior chamber. The incision size is critical with bimanual phaco. An incision that is too large compromises chamber stability, and one that is too tight restricts the movement of the instruments. A disposable 20-gauge MVR blade (Alcon Laboratories, Inc.) produces a reproducibly exact, 1.0-mm clear corneal incision that is the perfect size for the 20-gauge instrumentation.
Dr. Gravlee: When finishing a case or encountering trouble, a surgeon's natural reflex is to remove the second instrument (hook or chopper) first before removing the sleeved extraction probe. This technique prevents the eye from collapsing, but it must be reversed when using an irrigating chopper. The surgeon should remove the extraction probe before the irrigating chopper in order to prevent chamber collapse. The surgeon must learn this unnatural behavior.
Dr. Fishkind: There is a significant learning curve with bimanual phaco. Because the instruments move so tightly through the incisions, there are issues of “oarlock,” in which any lateral movement of the instrument tends to move the entire eye and distorts the cornea. Surgeons must learn how to move the instruments to and fro, similar to a piston, as they perform the procedure. If lateral movements are necessary, the incision must act as the fulcrum for the movement of the phaco tip or irrigating chopper, just like an oarlock for an oar. Surgeons can learn these techniques by performing bimanual I/A first. At the beginning of the phaco procedure, the surgeon should make two paracenteces and use one paracentesis for irrigation and one for aspiration. This method teaches the same principles as bimanual phaco, and the surgeon can learn how to use and maneuver the instruments before attempting phaco. Additionally, I believe this technique is best used in a phaco chop procedure, as manipulating these instruments for sculpting is difficult.
5. WHAT ARE THE DIFFERENCES BETWEEN THE FLOW AND VACUUM SETTINGS, AND HOW DO THESE AFFECT THE PERFORMANCE, CONTROL, AND SAFETY OF THE PROCEDURE?
Dr. Chang: With current 20-gauge instrumentation, surgeons must lower their conventional aspiration flow and vacuum rates to avoid surge when removing nuclear fragments. If I use high vacuum to impale the nucleus for chopping, I then switch to a lower vacuum memory setting for removing fragments.
Dr. Gravlee: The aspiration flow must be less than the irrigating flow. If the surgeon does not have power infusion capability, then the 19-gauge extraction probe must have a corresponding 19-gauge infusion. The same logic applies to 20- and 21-gauge extraction probes.
Dr. Fishkind: Inflow is very important. The bottle must be kept as high as possible above the eye, or there will not be adequate inflow (we use an IV pole extender to raise the bottle to approximately 70 cm above the eye). Also, the selection of the chopper is critical because the ports on the chopper restrict inflow, which is a major determinant of how well the chamber will be maintained. Tight incisions are important because any leak may reduce the reprodu-cibility of the entire formula. My personal approach is to lower my vacuum from my standard 315 mm Hg to 250 mm Hg and to lower my flow from my usual 24 cc/min to 20 cc/min. Those two parameters slow the procedure and better stabilize the anterior chamber. By bringing cataractous material to and holding it at the phaco tip, bimanual phaco allows the surgeon control and efficiency despite its less aggressive settings.
6. TO ADDRESS THE LEARNING CURVE, SHOULD FIRST-TIME USERS BEGIN WITH THREE INCISIONS IF ONE IS FOR AN IRRIGATION CANNULA?
Dr. Gravlee: Yes, this was the conclusion that I made when I wanted to convert to bimanual phaco. A self-retaining irrigating cannula allows the surgeon to use skills and techniques he has already developed. I was using a 19-gauge extraction probe at the time I wanted to convert to a sleeveless technique. None of the instrument catalogs had a 19-gauge, self-retaining irrigation cannula available, so I asked Storz Medical (St. Louis, MO), now Bausch & Lomb Surgical (San Dimas, CA), to make one for me. I decided that an elbow design would prevent it from being pulled accidentally out of the eye. The irrigation cannula works best when situated 180º from the cataract incision.
Dr. Fishkind: Chamber maintainers can be helpful, and some surgeons have used them; however, my experience with chamber maintainers is that, when using temporal incisions, the chamber maintainer will pass over the nose. This position will torque the inflow tube, and the resultant angle will direct fluid inflow into the iris. I believe that this fluid is traumatic and will affect the blood-aqueous barrier of the iris. Therefore, I do not use chamber maintainers. There is the potential for improvement if new chamber maintainers are designed specifically for bimanual phaco. While a chamber maintainer creates a deeper anterior chamber, I feel that dropping the vacuum and flow pressure and raising the bottle should sufficiently stabilize the chamber.
7. WHAT ARE THE DISADVANTAGES OF BIMANUAL PHACO USING ULTRASOUND?
Dr. Chang: The main disadvantage is that, compared to conventional phaco, the procedure is less forgiving with respect to incision size (must be exact), fluidics (easier to experience surge), and chopper maneuverability (more cumbersome and can lose inflow when retracted). It is a low inflow/outflow technique. Using high vacuum is more difficult and requires a machine that allows changing vacuum memory settings on the fly with the foot pedal. However, I can also imagine situations in which low flow/tight incision phaco might be advantageous. One case might be phaco with a zonular dialysis where viscoelastic is used to block off the vitreous. Another might be Fuchs' dystrophy, for which less total irrigation volume might be safer and might better preserve the viscoelastic shield.
Dr. Gravlee: A standardized technique has not been developed yet for cataract surgeons to use with bimanual phaco, so the technology requires a certain sense of adventure and creativity. For their initial cases, surgeons should choose a posterior subcapsular cataract with a 1+ or 2+ nuclear hardness to build confidence. They can easily convert to their usual technique to prevent any complications.
Dr. Fishkind: Bimanual phaco takes a little longer to perform, it is somewhat more difficult to maneuver the instruments, and there is currently no implant that can enter through the small incisions. Due to this lack of appropriately sized lenses, when I perform bimanual phaco, I plan a space in between the irrigating paracentesis and the phaco paracentesis through which I can create a separate incision to insert the implant. Surgeons must be careful not to enlarge or stretch the paracenteses in any way or they will become difficult to close without sutures.
Additionally, there are times when the material being emulsified will actually spindle on the sleeveless phaco tip. The tip will puncture right through the fragment, which will then slide down the tip, forcing the surgeon to pull the tip back and immobilize the fragment in order to access it (I call this nuisance spindling).
Finally, once the ThinOptX implant (ThinOptX Inc., Abingdon, VA) or other microincisional IOLs become available, bimanual phaco will be a very nice procedure. Without such lenses, there is not a compelling reason to perform the technique. However, just as large-incision phaco procedures transitioned to small incision phaco when foldable implants became available, bimanual phaco will be very useful with the next generation of lenses.
David F. Chang, MD, is Clinical Professor at the University of California, San Francisco, and is in private practice in Los Altos, California. He is a consultant for Advanced Medical Optics, Inc., and holds no financial interest in any product or technology mentioned herein. Dr. Chang may be reached at (650) 948-9123; firstname.lastname@example.org.
Joseph F. Gravlee, Jr, MD, MSEE, ABES, is in private practice at the Bay Eyes Cataract and Laser Center, P.C., in Fairhope, Foley, and Daphne, Alabama. He holds no financial interest in any technology or product mentioned herein. Dr. Gravlee may be reached at (251) 990-3937; email@example.com.
William J. Fishkind, MD, FACS, is Clinical Professor at the University of Utah in Salt Lake City and Director of the Fishkind and Bakewell Eye Care And Surgery Center in Tucson, Arizona. He also serves as Clinical Instructor at the University of Arizona in Tucson. He is a consultant for Advanced Medical Optics, Inc., but holds no financial interest in any product or technology mentioned herein. Dr. Fishkind may be reached at (520) 293-6740; firstname.lastname@example.org.
1. Masket S, Tennen DG. Astigmatic stabilization of 3.0 mm temporal clear corneal cataract incisions. J Cataract Refract Surg. 1996;22:1451-1455.