For the past decade, cataract surgeons have been following the progress and development of laser phaco systems with great interest.1-6 This technology has always promised two potential advantages. First, a system that prevents heat build up and wound burns would make possible a bimanual technique that uses separate infusion and aspiration lines through paracentesis-sized incisions. I use the term cold phaco to describe any emulsification technology that does not generate a hot instrument tip (less than 45&Mac251;C). Second, reducing the energy levels delivered into the eye might lessen trauma to such tissues as the corneal endothelium. The first laser phaco machine, the Dodick Laser PhacoLysis System manufactured by A.R.C.Laser Corporation in Salt Lake City, UT received FDA approval in August 2000. However, the first system able to deliver on both of these promises ironically may instead be a software-modified, conventional ultrasound machine.
New Cold Phaco Technologies
In the United States, we can now use one of three new “cold phaco” technologies that were not available to us a year ago. At the end of 2000, STAAR Surgical of Monrovia, CA, introduced their Sonic Wave technology, signaling a true paradigm shift. Instead of ultrasound (20,000-40,000 Hz), it uses sonic frequencies (40-400 Hz) to power a conventional phaco handpiece and needle. This lower frequency avoids heat build up, as demonstrated by the surgeon's ability to touch the vibrating tip without being burned. Furthermore, the STAAR Sonic Wave machine can also deliver conventional ultrasound via the same phaco handpiece and needle. A footpedal-controlled switch can initiate the change from ultrasound to sonics, and back.
In my own experience, I was impressed with how well sonics worked with soft and medium nuclei. However, it was clearly slower and less efficient for denser nuclei compared to ultrasound, and quite ineffective for brunescent nuclei. Most users seem to share this observation. Even so, sonics has one important advantage over current laser phaco systems. If the surgeon needs to abandon sonics in mid-operation for conventional ultrasound, one can rapidly make the switch without having to change the machine or handpiece. I usually found that with denser nuclei it was necessary to revert back to ultrasound.
WhiteStar: Hyper-Pulse Technology for the Sovereign
Later this year, Allergan will introduce a new option for the Sovereign phaco system called WhiteStar. This machine already features superb fluidics and a digitally controlled handpiece that offers exceptional cutting ability. This new technology upgrade will prevent significant heating of the ultrasound tip, without having to modify the handpiece.
The WhiteStar technology represents a paradigm shift toward a different direction—a new form of pulse/burst mode. The WhiteStar extends the benefits of Pulse/Burst Mode to a new level. First, by shortening the duration of the phaco pulses relative to the pauses, the “on/off” ratio can be lowered even further. Compared to the 100% “on” time of continuous phaco, and the 50% net “on” time of conventional Pulse Mode, the WhiteStar phaco pulses are “on” for only 25 to 33% of the cycle (Figure 1). Predictably, this results in an even greater reduction of chatter. Second, the number of pulses per second can be exponentially increased to create a type of “hyper-pulse.” The rapid interruption and fragmentation of phaco time prevents heat buildup at the tip. However, because the individual pulses are still driven by digitally tuned, full frequency ultrasound, there is no functional loss of cutting efficiency.
Sonics and WhiteStar (Hyper-Pulse) Compared
Sonics and WhiteStar both modulate power delivery from a traditional phaco handpiece through software and computer modifications. Because the hardware doesn't change (the same handpiece is used), both of these new power modes can be seamlessly integrated and alternated with standard ultrasound modes during any given case. Such flexibility currently gives each of these technologies a major advantage over laser phaco.
Both sonics and hyper-pulse decrease energy and heat production, and with both you can touch the bare, vibrating phaco needle with your fingers. However, at sonic frequencies, the oscillating phaco tip appears to lose force and acceleration. Heat is reduced, but cutting power is sacrificed.
In contrast, the WhiteStar mode maintains full ultrasonic power that is pulse-interrupted frequently enough to prevent heat buildup. Like the traditional Pulse Mode, this “hyper-pulse” reduces the amount of energy delivered without sacrificing cutting ability. As a result, the Sovereign WhiteStar technology excels across the entire spectrum of nuclear densities regardless of the surgical technique. The surprising efficiency by which WhiteStar removes brunescent nuclei is clearly what sets this technology apart from sonics and laser phaco.
Initial Clinical Results
I am one of several surgeons who have had developmental access to this hyper-pulse technology. After using WhiteStar in more than 200 cases covering a continuum of nuclear densities, I have been impressed by five clinical observations.
First, there has been no need to alter my standard Sovereign settings, phaco tip, instrumentation, or chopping technique when using this new software. Regardless of nuclear density I routinely use a 30&Mac251;, 20-gauge micro tip to perform horizontal or vertical phaco chop without any sculpting. For denser lenses, traditional burst mode with 400 mm Hg vacuum is used to maximize nuclear purchase for the chopping steps. The WhiteStar “hyper-pulse” mode is then activated for the phaco-assisted aspiration of the chopped fragments and epinucleus. For a divide-and-conquer method, WhiteStar can also perform sculpting.
Second, the effective phaco times (EPTs) for a given nuclear density are lower than I customarily obtain with the Sovereign using the identical settings and technique. This presumably is the result of the ultrasound being “on” for only 25% of the WhiteStar Pulse Mode cycle versus 50% of the standard Pulse Mode cycle.
The third and most important conclusion is that this technology is extremely efficient and effective at emulsifying brunescent nuclei. I have successfully utilized this software to perform phaco chop in twelve 4+ cataracts, including three ultrabrunescent, “mahogany” lenses. No sculpting was required in any of these cases and the average EPT for this series was 9.3 seconds, with a range of 6 to 20 seconds.
The fourth observation is an obvious improvement in followability with dense nuclear material. Because rigid pieces do not easily mold into the tip, chatter is exaggerated with brunescent nuclei and with micro phaco tips. By decreasing the repelling forces of the phaco tip as described earlier, the “hyper-pulse” mode eliminates chatter with dense nuclei. The particles actually seem to hug the phaco tip without the momentary separation normally seen during emulsification.
Finally, although pachymetries were not measured, the postop day 1 corneas seem to be consistently clearer after using this new modality. Because the phaco energy and EPTs are already minimized by the phaco chop technique,7 I attribute this further improvement to decreased turbulence of particles in the anterior chamber. Therefore, improved followability and decreased chatter not only enhance efficiency, but may decrease endothelial trauma as well.
The Goal: Improved Safety
Although laser phaco and sonics both decrease energy and heat delivery, they are ineffective for brunescent nuclei—the very cases for which these advantages are most desired. In contrast, the WhiteStar “hyper-pulse” mode is “cold” ultrasound. By preserving the full ultrasound frequency, it is able to emulsify the densest nucleus while still avoiding a hot phaco needle. Endothelial safety is potentially improved in three ways: eliminating the risk of thermal injury permits a tighter incision to be constructed, which should reduce total anterior chamber infusion volumes; reducing the phaco “on/off” ratio lowers total energy delivery (EPT) into the eye; and finally, decreasing the repelling force of the phaco tip lessens the turbulence of nuclear particles in the anterior chamber. At this time, these hypotheses need validation from clinical studies.
Future Applications
A cold ultrasound system will permit cataract removal via separate irrigation and phaco-aspiration instruments. Such a bimanual phaco technique could be performed through a paracentesis-sized incision. This would create demand for a paracentesis-insertable intraocular lens technology. In addition to laser probes, others have experimented with this technique using standard ultrasound with a sleeveless phaco needle for this purpose.8,9 Nevertheless, there is always the potential for significant wound burn using traditional ultrasound. Randall Olson, MD, has been investigating and developing a bimanual ultrasound system using the WhiteStar technology that he called “micro-phaco.”
In addition to the prospect of smaller incisions, bimanual phaco might provide supplementary fluidic advantages. A tighter incision can be used for the phaco tip to minimize leakage alongside the shaft, without the risk of burns. This would decrease the total volume of fluid infused through the eye, and isolate the phaco tip lumen as the sole outflow exit. In addition, the traditional coaxial irrigation sleeve creates unwanted counter-currents between the competing inflow and outflow streams. Separate inflow and outflow ports might produce a much more efficient, shunt-like flow system that will reduce irrigation volumes, ultrasound times, and pump vacuum/flow settings.
David F. Chang, MD is a clinical professor at the Univeristy of California, San Francisco. Dr. Chang is a consultant for Allergan. (650) 948-9123; dceye@earthlink.net1. Dodick JM: Laser phacolysis of the human cataractous lens. Dev Ophthalmol. 22:58-64, 1991.
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6. Kanellopoulos AJ, et al: A prospective clinical evaluation of 1000 consecutive laser cataract procedures using the Dodick Photolysis neodymium: Yttrium-aluminum-garnet system. Ophthalmology 108:1-6,2001
7. DeBry P, Olson RJ, Crandall AS: Comparison of energy required for phaco-chop and divide and conquer phacoemulsification. J Cataract Refract Surg 24:689-692, 1998
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9. Tsuneoka H, Shiba T, Takahashi Y: Feasibility of ultrasound cataract surgery with a 1.4 mm incision. J Cataract Refract Surg 27:934-940, 2001
