Surgical results and implications

Successful phacoemulsification surgery is a delicate balance of complex forces. On the one hand, energy is required to separate and remove the hardened nuclear material. On the other hand, a significant imbalance of fluidics and/or energy delivery can cause unwanted trauma to the eye.

The basic elements of phaco, particularly longitudinal ultrasound, have been in use for nearly 40 years. The forward-and-backward movement of the tip in traditional phaco is the gold standard for cataract removal with a low rate of complications that enable a quick and successful visual recovery for patients. Surgeons have taken advantage of system parameters, such as sophisticated software modulations of energy delivery and constant adjustments in irrigation and aspiration rates, to limit the potential negative effects of the competing fluidic and energy parameters. It has been a matter of accentuating the positive aspects of phaco surgery and technology, while limiting those aspects that could result in negative outcome.

One of the primary objectives of phaco is keeping lens material at the tip so that energy can be efficiently applied into the nuclear tissue. Surgeons must balance the use of vacuum pressure and aspiration flow rates that are high enough to clear the nuclear tissue efficiently, but low enough to reduce fluid usage and post occlusion surge. Optimally balanced salt solution use should be kept to a minimum. The efficiency of the system should enhance the skill of the surgeon in chopping and clearing the cataract material from the eye without causing undue risk, corneal edema and chamber instability that could result in inadvertent rupture of the posterior capsule.

Reducing repulsion

Numerous studies of the OZil handpiece and the Infiniti Vision system (both from Alcon Laboratories, Inc., Fort Worth, Texas) have demonstrated that it results in less balanced salt solution usage and surgery that is more efficient, without loss of safety. The equilibrium between fluid irrigated into the anterior chamber and material aspirated from the anterior chamber is crucial to phaco.

High balanced salt solution use, combined with turbulence and chatter, are the primary causes of corneal edema following modern cataract surgery, said Robert Cionni, MD, of the Cincinnati Eye Institute, Ohio, in a scientific presentation at the American Society of Cataract and Refractive Surgery meeting.¹ In his experience, more balanced salt solution flow through the chamber, especially if it is turbulent due to chatter from the phaco tip, increases the risk of endothelial cell loss and edema. Chatter also increases the need to “chase” and emulsify nuclear pieces in the anterior chamber.

One of the surgical benefits of torsional phaco is the reduced usage of balanced salt solution.
—Robert Cionni, MD

Traditionally, corneal edema has been associated with greater energy use when performing traditional phaco procedures. This is typical of surgeries with denser nuclei that take longer to perform. Longer ultrasound times are typically accompanied by increased energy levels and chatter of lens material, resulting in anterior chamber turbulence and even more use of balanced salt solution throughout the procedure.

One of the surgical benefits of torsional phaco is the reduced usage of balanced salt solution. This is important, according to Dr. Cionni, because it is a marker for less turbulence and chatter. In a study using the Infiniti vision system, measuring balanced salt solution usage in a total of 15 longitudinal and 23 torsional phaco cases, torsional phaco used less balanced salt solution during nucleus removal in the study: 35.7 mL vs. 40.2 mL. He also studied surgical efficiency of lens removal for each group, and his results showed less time was required for nucleus removal with the torsional patients.

According to Dr. Cionni, the reduction in balanced salt solution was due to less chatter of lens material and less turbulence of fluid in the anterior chamber. Decreased repulsion of lens material kept material on the tip which decreased the amount of balanced salt solution required to draw lens material back to the tip. Overall, this combination of reduced chatter and turbulence, and improved efficiency, means less chance for corneal edema, according to Dr. Cionni. (Figure 1)

Demonstration of improved cutting effectiveness using less fluid, reduced nucleus removal time and lower effective ultrasound power

Figure 1. In comparing longitudinal and torsional phaco, Dr. Cionni found a reduction in fluid use (A), nucleus removal time (B) and effective ultrasound power (C). These measures are important, he said, because they indicate less chatter and turbulence. In other words, less power used and less time in the eye indicate smoother cutting action and constant contact with the cataract, which results in less fluid used.¹

The improved fluidics profile of torsional ultrasound leads to improved performance in the operating room. The constant contact with the nucleus afforded by torsional ultrasound creates efficient cutting and evacuation of nuclei through all lens densities. Because there is no disruption of contact with the nucleus, surgery times are often decreased with better results.

“The use of torsional phaco for progressing cataracts results in improved patient outcomes, and torsional phaco is a safe and viable new technology for the emulsification of any density of cataract,” Fernando Z. Aguilera, MD, of Instituto de Ojos said at a presentation at the ASCRS meeting.²

Dr. Aguilera compared 214 cases, half performed with torsional phaco with the OZil handpiece and Infiniti Vision System, and half using traditional ultrasound with a Legacy 20000 Advantec (Alcon Laboratories, Inc.) system. There was no overall difference in ability to sculpt the dense cataracts with respect to longitudinal and torsional phaco. A distinct difference in performance occurred, he said, during the segment or quadrant removal process, where there was less repulsion with torsional phaco due to steady contact of the tip and lack of repulsion of the lens material because of the side-to-side movement.

The torsional phaco surgeries employed less energy, were more efficient and required significantly less balanced salt solution. Another important finding of his study is that patients undergoing torsional phaco experienced less endothelial cell loss and had less corneal edema measured by pachymetry after surgery. There was a 26% reduction in balanced salt solution use during torsional phaco compared to longitudinal phaco. (Figure 2)

“The use of less delivered energy and less fluid flow through the eye is desirable in every phaco procedure in order to diminish the possibility of endothelial cell loss,” Dr. Aguilera said. “The best corrected visual acuity was similar in both groups,” he said, but there was considerable surgical benefit to using torsional vs. longitudinal phaco. There was 8% less loss of endothelial cells in eyes after torsional vs. longitudinal phaco. Using pachymetry, Dr. Aguilera observed a 23% reduction in corneal swelling in eyes treated with torsional ultrasound compared to longitudinal phaco. (Figure 2)

“We can conclude that torsional phaco with Infiniti shows improved fluidics and systemetrics as compared to linear phaco with the Legacy Advantec,” said Dr. Aguilera.

Comparison of surgical results and outcomes

Figure 2. Dr. Aguilera found reduced use of balanced salt solution and delivered dissipated energy, which resulted in reduced corneal swelling and less endothelial cell loss when comparing Infiniti torsional ultrasound with Legacy traditional ultrasound.²

Repulsion and micro-repulsion

Improved performance was also found by David Allen, FRCS, of Sunderland, England, who presented objective evidence at the ASCRS meeting of the increased efficiency of torsional phaco in a study measuring the volume of balanced salt solution used during the actual removal of the nucleus.³ Mr. Allen assigned 42 patients each to receive either longitudinal or torsional phaco. He and his staff weighed the balanced salt solution bottle during each surgery at the beginning of nucleus removal and again at the end of nucleus removal.

The corneal endothelium is not designed to have large volumes of fluid flowing over it, especially potentially turbulent flow as might be seen with phaco surgery on hard cataracts with traditional ultrasound, according to Mr. Allen. “It is commonly accepted that where possible, ophthalmologists should minimize the amount of this fluid that flows through the eye,” he said.

Patients undergoing torsional phaco required significantly less balanced salt solution during nucleus removal, averaging 42 mL compared to the 55 mL used during longitudinal phaco, a reduction of 22% with torsional. (Figure 3) Mr. Allen believes these findings are compelling and is now looking into demonstrating the clinical significance in future studies.

“Longitudinal motion encourages repulsion, reduces followability and reduces efficiency. By contrast, the torsional motion greatly removes repulsion.”
—David Allen, FRCS

Nucleus removal time was reduced in the group undergoing torsional phaco, Mr. Allen said, and, although difficult to measure, repulsion was also reduced. Torsional ultrasound, he said, reduced the two common types of repulsion in traditional phaco.

The more common occurrence involves nuclear fragments being repulsed completely away from the tip, leaving the tip to travel around the anterior chamber forcing the surgeon to move the tip within the anterior chamber. Dislodged nuclear material and turbulence within the anterior chamber can lead to corneal endothelial cell loss.

There is also a problem of “micro-repulsions,” visible only on slowed-down video footage, according to Mr. Allen. Micro-repulsions occur when material is repulsed slightly away from the tip by phaco power, only to be drawn back to the tip by system fluidics. After analyzing slow motion video of torsional and traditional phaco, it became clear that these micro-repulsions do not occur with torsional phaco, and constant contact with the nucleus is maintained, Mr. Allen added.

“Longitudinal motion encourages repulsion, reduces followability and reduces efficiency. By contrast, the torsional motion greatly removes repulsion, and therefore results in improved followability that is required for overall less manipulation within the anterior chamber,” said Mr. Allen.

Comparison of fluid use

Figure 3. Mr. Allen noted a 22% reduction in balanced salt solution use with torsional compared to longitudinal phaco.³

Altering fluid dynamics and parameters

There is still another important element to the amount of infused fluid: usage in relation to vacuum and aspiration flow levels. Traditional longitudinal phaco is most efficient when attraction of the lens to the tip is at increasing higher levels of vacuum and flow. In the traditional system, attraction is a result of high aspiration flow rates and vacuum pressure, working from inside the tip of the handpiece, and intraocular irrigation pressure, pushing from the other side of lens material. These combine to keep lens material on or near the phaco tip.

If the attractive force is low and repulsion is high, cutting efficiency is diminished. Higher attracting fluidic forces are desirable with longitudinal phaco because they will attract and hold the lens material onto to the tip, making every forward stroke as productive as possible.

Yet high vacuum settings have inherent disadvantages. High vacuum demands increased fluid infusion capacity, which can be problematic. There is an increased risk of post occlusion surge that could cause inadvertent damage to ocular structures that are inadvertently drawn to the tip, such as the iris or corneal tissue.

With torsional phaco, there is less chatter and virtually no repulsion, so the fluid flow within the anterior chamber is less turbulent. In addition, due to the efficiency of the entire system, high flow and vacuum levels are not as necessary to maintain attraction as compared to traditional longitudinal ultrasound.

To illustrate this point, Richard J. Mackool, MD, of the Mackool Eye Institute in New York, used high speed, slow-motion video to demonstrate a lack of chatter with torsional phaco in a presentation at the ASCRS meeting.⁴ He found that this translates into less overall energy and a reduction of flow rate and vacuum levels required to rapidly remove the cataract. With respect to vacuum power, he said that the efficiency of the cutting action and constant contact with the tip means that surgeons do not need to resort to extremely high vacuum and flow levels to overcome repulsion. In traditional longitudinal phaco surgery, it is common to do this to achieve the necessary holding force needed to break the lens material.

“Lower flow and vacuum parameters can be used [with torsional phaco] because high attractive forces are not required to hold the lens at the tip,” said Dr. Mackool.

References

Cionni R. Torsional to longitudinal phacoemulsification comparison. Presented at: Annual Meeting of the American Society of Cataract and Refractive Surgery; March 17-22, 2006; San Francisco.

Aguilera F. Comparing outcomes of linear phaco technology vs torsional phaco technology in the emulsification of cataracts. Presented at: Annual Meeting of the American Society of Cataract and Refractive Surgery; March 17-22, 2006; San Francisco.

Allen D. Efficient surgery with a new torsional phaco mode. Presented at: Annual Meeting of the American Society of Cataract and Refractive Surgery; March 17-22, 2006; San Francisco.

Mackool R. Torsional phaco: the elimination of lens chatter and thermal energy. Presented as an Alcon booth presentation at: Annual Meeting of the American Society of Cataract and Refractive Surgery; March 17-22, 2006; San Francisco.