Advanced phaco tip design makes surgery safer

Steven H. Dewey

Regardless of meticulous preparation, there is always a possibility that surgery will not proceed as anticipated. Some incidents are overcome and quickly forgotten. Others leave the patient and surgeon with a tangible reminder of an unfortunate and unanticipated complication of an otherwise routine procedure.

Ophthalmology is an imprecise science. Some complications, such as cystoid macular edema, result from the normal trauma of surgery. These patients will still have an anatomically stable pseudophakic eye, and treatment may completely resolve the problem. Other complications, such as ruptured capsules and damaged irises, tend to occur sporadically, and guarantee a compromised result.

Although it is recognized that complications may occur in surgery, can ophthalmologists determine whether an acceptable complication rate exists? Is the rate different for refractive lens exchange than it is for cataract surgery? How can surgeons reduce the trauma of routine surgery and still prepare for the unexpected?

Changing the rules

Sessions dedicated to preventing complications provide surgeons with useful recommendations for reducing the likelihood of specific complications. This type of situation-specific proactive approach may be effective, but may be comparable to trying to recognize when to fasten the seat belt just before an accident. Other strategies deal with the complication after the event. The posterior-assisted levitation (PAL) technique,¹ for example, improves the outcome in the face of an intraoperative disaster. Regardless of how the capsule tore, I have sometimes used viscoelastic to retrieve a falling nucleus, although the percentage of cases in which I have used the PAL technique is low. The patient, however, is still left with all of the potential consequences of a ruptured capsule.

I strongly prefer the proactive approach of avoiding as many complications as possible without having to anticipate each one. This approach may seem simplistic, but both patients and surgeons would benefit if surgeons were not worried about how to rescue a falling nucleus or suture a shredded iris. One potential solution is now thoroughly tested, and demonstrably improves the odds of surviving a chance encounter with the iris or capsule.

The Dewey Radius Tip (MicroSurgical Technology) is a phaco needle with no sharp edges. The edges along the inner and outer rims of the tip have been rounded with exacting precision. However, it is exactly like the phaco needle one would otherwise use, with similar gauges, bends, and bevels. The tip functions nearly identically to its sharp-edged counterparts for any surgical technique, and requires no changes in phaco machine parameters.

Challenging the concepts

The primary intent in this needle design is safety. Without a sharp edge, the needle will not inherently cut tissue through simple contact. This is true for both the outer edge of the needle where the majority of passive tissue contact would occur, and the inner edge where the effects of vacuum and ultrasound would be expressed. Many surgeons have embraced the idea that the rounded edge serves the same purpose as a safety belt. Although the odds of having a traffic accident are significantly low, it is best to be prepared for the unexpected.

Other surgeons are appropriately slightly more skeptical. Phaco needles have been manufactured on the premise that the needle must be extremely sharp to cut the cataract. In this view, rounding the edges may make the needle too inefficient to justify the improvement in safety. The argument in favor of a sharp tip also involves the capsule’s ability to resist puncture by vacuum or ultrasound application. Surgeons were taught during residency that vacuum alone could puncture the capsule, and that mere contact with ultrasound will cause a nearly immediate rupture. Thus, if the capsule will break due to vacuum or ultrasound alone, it makes little sense to worry about whether the edge is sharp because it cannot be allowed to touch the capsule.

Unfortunately, this view of needle design is reinforced when a sharp tip contacts the capsule because surgeons are more likely to puncture the capsule than preserve it.

Alternative needle innovations

Over the years, many innovations reduced the potential for damage caused by the sharp needle. In the early 1990s, Peter Davis, MD rounded the outer edge of the phaco needle to facilitate passage through the incision and to allow the tip to contact the capsule and iris without cutting them. His tip design emphasized a shaped inner rim in an attempt to focus ultrasound energy. Later, Joseph F. Gravlee, MD blunted the sharp edge of the bevel, enabling the tip of the needle to contact the capsule without damaging it. These were steps toward a rounded needle, with Dr. Davis’s design retaining the sharp inner edge of the needle and Dr. Gravlee’s design retaining most of the sharp inner and outer edges.

Takayuki Akahoshi, MD created a needle called the “Knuckle Tip” (ASICO). Rather than having the standard wall thickness extend through the entire length of the needle, he created a bulbous tip design with round edges on all surfaces. This bulbous design avoids occluding the posterior capsule with the phaco needle, therefore aspirating only nuclear and cortical material. While both Dr. Davis’ and Dr. Gravlee’s tips were designed for use without changing techniques, the Knuckle Tip is most efficient with a pre-chop.

Clinically effective

I was concerned that the rounded needle would not be as efficient at removing cataracts as a sharp needle, or that the needle would behave differently than a sharp tip, and require either changes in technique or phaco parameters to make it useful. Although preoperative planning for an individual case is paramount in importance, I do not advocate changing techniques or technologies depending on nucleus density. I prefer to plan for a dense cataract and tailor my technique and settings to suit the delicacies of a softer nucleus, rather than take an inefficient technology used for softer cataracts and attempt to apply it to denser ones.

To test the efficiency of the rounded needle, I used the WhiteStar Signature System with Fusion Fluidics (Advanced Medical Optics [AMO]). I found that the WhiteStar and the WhiteStar increased control efficiency (ICE) system improved efficiency of micropulse or “cool” phaco. Compared with traditional longitudinal phaco, micropulse delivery significantly reduces the temperature of the phaco needle² at the incision by delivering the power in bursts lasting milliseconds. The gaps between the bursts allow for cooling of the tip.

Reducing the risk of incision burns, however, was not as important to me as the other factors visualized intraoperatively. The micropulse delivery nearly eliminated chatter and turbulence, which significantly decreased the incidental trauma of a routine case. In addition, the phaco power used to remove a nucleus decreased.³ In a presentation in early 2002, Dr. Mark Shafer described the phenomenon of transient cavitation. By delivering power in micropulses, each pulse delivers more power than an equivalent time period of continuous phaco power. The benefit of transient cavitation in reducing power is reduced stress on an eye for routine surgery. Although this benefit may not be significant for softer cataracts, the benefit grows proportionally with the density of the lens.

Over several months, I found that the rounded phaco needle was equally as effective at removing 2+ and 3+ cataracts as a sharp needle. I started slowly, first working with softer 2+ NS (on a 1+ to 4+ scale), with no other changes to the surgery besides the needle design. I expected these patients to need little or no phaco power. I found the parameters of equivalent phaco time (EPT), foot pedal time (FPT), and average power to be nearly identical to cases with the sharp edge. Reviewing the videotapes of several hundred procedures, I found the time the phaco needle spent in the eye was also the same, suggesting that I had not altered my technique to account for the needle configuration.

I gradually expanded the density of cataracts to 3+ and even 4+ nuclei. Again, a thorough review of the videotapes of the procedures showed the rounded needle behaved similarly to the sharp needles without changing other aspects of the surgery. The measured EPT, FPT, average power and “tip time” were close in range. Although my primary technique is a horizontal chop, I found similar results with nuclear flipping and divide-and-conquer approaches as well.

These findings demonstrated that when using modern phaco technology, the sharp edge is not necessary to efficiently remove a cataract.

Validating the rounded tip design

Some surgeons accidentally capture the capsule for a microsecond but without adverse consequences. Cutting requires more than just contact. It requires movement against a stable surface. The Dewey Radius Tip was effective at preventing damage from incidental contact, even with higher levels of vacuum, but I wondered how significantly ultrasound could damage the capsule.

At the Moran Eye Center, University of Utah, Dr. Nick Mamalis, Dr. Liliana Werner and I performed cadaver studies to evaluate the safety of the Dewey Radius Tip. Previous efforts with cadaver eyes showed that the capsule can survive significant amounts of vacuum without apparent damage. I was not certain that ultrasound could be applied to the capsule; however, my colleagues and I found that we could contact the capsule without tearing it and apply as much as 50% phaco power at 400 mm Hg vacuum for extended periods before the capsule ruptured (Figure).

We determined the limits of the capsule by rupturing the capsules of 12 cadavers, with 11 of the 12 surviving extended contact with vacuum and ultrasound. One capsule ruptured early because of mishandling the Radius Tip. This study showed that the capsule has a greater resilience to the effects of ultrasound than I had previously thought. Although I firmly believe that any capsule can rupture at any time, I think that most iatrogenic damage is a result of a phaco needle’s sharp edge, and not the intrinsic effects of vacuum and ultrasound.

Dewey Radius Tip Figure: The Dewey Radius Tip applying 20% power at 100 mm Hg for 9.5 seconds prior to capsule rupture. While the rounded edge design undoubtedly protected the capsule from immediate damage, it is likely that the micropulse power modulations of WhiteStar ICE further reduced the risk of thermal damage to the capsule. Source: Dewey S

Role of the phaco platform

Regardless of how effectively instrumentation can enhance safety during surgery, I find that the WhiteStar Signature System with Fusion Fluidics is a primary means to prevent complications. In my experience, the efficiencies of micropulse technology improve patient safety. The system also offers advanced safety features with its Fusion Fluidics technology.

The Fusion Fluidics component has two main advantages. First, it offers both a peristaltic and a true venturi dual pump system. With the WhiteStar System, surgeons no longer have to choose a platform based on pump design but can change vacuum formats to accommodate individual techniques.

A significant safety feature of Fusion Fluidics is found in the chamber monitoring software. Every 30 ms, the anterior chamber environment is evaluated. As occlusion is achieved and vacuum builds, this vacuum level is held long enough to allow for good apposition of the nuclear fragment with the tip of the needle. The break in occlusion is anticipated by reducing the vacuum to a preset level. When occlusion breaks, chamber bounce is minimized and true surge is virtually eliminated to achieve maximum chamber stability.

Synergies

In my experience, the WhiteStar Signature System has no learning curve. I have performed divide and conquer, chops, and flips with this machine and have found it to be a reliable platform with a number of advanced features that enhance my procedure. Add to this the safety of the Dewey Radius Tip, and the result is a greater sense of confidence. The Dewey Radius Tip is precise enough to polish the posterior capsule, even using ultrasound.⁴ Observing this needle in action demonstrates its greater reliability as opposed to the liability of a sharp edge.

Conclusion

The paradigm must change as ophthalmology transitions from the cataract surgery standards of the last century to the new standards of refractive lens exchange. Surgical outcomes previously acceptable to patients with impaired vision will no longer be considered sufficient. Ophthalmologists’ historical perspectives do not burden patients’ needs and goals. Complication management is inevitable. The advantages of proactive complication avoidance may be difficult for an individual surgeon to measure, but the advantages to the patient are incalculable.

Surgeons will develop confidence with these standards as they gain experience and see how improved instrumentation and technology allow them to advance their technique. The Dewey Radius Tip and WhiteStar technology are two innovative solutions that allow surgeons to meet the challenges of success.

Reference

1. Chang DF, Packard RB. Posterior assisted levitation for nucleus retrieval using Viscoat after posterior capsule rupture. J Cataract Refract Surg. 2003;29(10):1860-1865.
2. Soscia W, Howard JG, Olson RJ. Microphacoemulsification with WhiteStar. A wound-temperature study. J Cataract Refract Surg. 2002;28(6):1044-1046.
3. Fishkind W, Bakewell B, Donnenfeld ED, Rose AD, Watkins LA, Olson RJ. Comparative clinical trial of ultrasound phacoemulsification with and without the WhiteStar system. J Cataract Refract Surg. 2006;32(1):45-49.
4. Dewey SH. Ultrasonic Polishing of the Posterior Capsule With the Dewey Radius Tip. Techniques in Ophthalmology. 4(4):139-148, December 2006.

Dr. Dewey practices at Colorado Springs Health Partners, P.C. in Colorado Springs, CO.