Tutorial
Introduction
New Cold Phaco Technologies
Initial Clinical Results
The Goal: Improved Safety
Future Applications
References
Slides
Cold Phaco for Brunescent Nuclei
David F. Chang, MD
For the past decade, cataract surgeons have been following the progress and development of laser phacoemulsification systems.1-6 This technology has always promised two potential advantages. First, a system that prevents heat buildup 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°C). Second, a reduction in energy levels delivered into the eye may reduce trauma to such tissues as the corneal endothelium. The first laser phaco machine, the ARC Dodick Photolysis system (Laser Corp, Salt Lake City, Utah), received Food and Drug Administration approval in August 2000. However, the first system able to deliver on both of these promises instead may be a software-modified, conventional ultrasound machine.
In the United States, three new cold phaco technologies are available. Much has been written about Erb:YAG laser cataract systems. However, cold phaco is a technology that is still in development. Although cold phaco has achieved excellent results with soft and medium density cataracts, brunescent nuclei pose limitations for it. Proponents remind us that ultrasound systems evolved through several generations of less sophisticated technology. Howver, this significant limitation in removing brunescent cataracts must be overcome before purchase of this alternative hardware can be justified on a widespread basis.
At the end of 2000, Staar Surgical (Monrovia, Calif.) introduced the Sonic Wave technology, signaling a true paradigm shift. Instead of ultrasound (20,000 Hz to 40,000 Hz), the Sonic Wave uses sonic frequencies (40 Hz to 400 Hz) to power a conventional phaco handpiece and needle. This lower frequency avoids heat buildup, as demonstrated by the surgeon’s ability to touch the vibrating tip without being burned. Furthermore, the Sonic Wave machine can also deliver conventional ultrasound via the same phaco handpiece and needle. A foot-pedal 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 ineffective for brunescent nuclei. Most users seem to share this observation. However, sonics has one important advantage over current laser phaco systems. If a surgeon needs to abandon sonics mid operation for conventional ultrasound, he or she can rapidly make the switch without changing the machine or handpiece. I usually found that with denser nuclei it was necessary to revert back to ultrasound.
Whitestar
In 2002, Allergan (Irvine, Calif.) introduced a new option, Whitestar, for the Sovereign phaco system. The Sovereign already features
efficient fluidics and a digitally controlled handpiece that offers exceptional cutting ability. The Whitestar upgrade prevents significant
heating of the ultrasound tip, without requiring a different handpiece.
The Whitestar technology represents a paradigm shift toward a different direction — a new form of pulse/burst mode. Let’s review what happens in a traditional pulse mode setting, such as with four pulses per second. During each full second of time (1,000 msec) spent in foot position 3, there are four discreet 125-msec pulses of phaco "on" time, which alternate with four 125-msec periods of phaco "off" time. The ratio of ultrasound on time to ultrasound off time is 50%. Compared to continuous mode (always on), pulse mode, therefore, cuts the phaco time in half.
A benefit of pulse mode is improved followability of the fragments being emulsified at the tip. "Chatter," which is the yo-yo like movement of nuclear pieces alternately contacting and separating from the phaco tip, occurs because of the opposing forces of suction (pump) and repulsion (tip oscillation) acting upon the nuclear material during continuous ultrasound. As phaco power increases, e.g., from 10% to 40%, the ultrasound frequency remains constant. It is a greater axial stroke length of the oscillating needle that generates the increased power. This explains why excessive phaco power actually kicks nuclear particles away. Compared with continuous mode, pulse mode interrupts the tip oscillation 50% of the time, favorably shifting the balance between these opposing forces at the tip.
The Whitestar technology 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. 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 hyperpulse. It is the rapid interruption and fragmentation of phaco time that 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 versus Whitestar
Sonics and Whitestar both modulate power delivery from a traditional phaco handpiece through software and computer modifications.
Because the hardware does not change (same handpiece), both of these new power modes can be seamlessly integrated and alternated
with standard ultrasound modes during a given case. Such flexibility gives each of these technologies a major advantage over laser phaco.
Both sonics and hyperpulse were developed out of the realization that continuous mode ultrasound provides more energy than is necessary to do the job. Both systems decrease energy and heat production; with both, the bare vibrating phaco needle can be touched with the 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 traditional pulse mode, this hyperpulse 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 what sets this technology apart from sonics and laser phaco.
I am one of several surgeons who has had developmental access to this hyperpulse technology. After using Whitestar in more than 800 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 the Whitestar software. Regardless of nuclear density, I routinely use a 30°, 20-gauge microtip to perform horizontal or vertical phaco chop without sculpting. For dense lenses, traditional burst mode with a 400-mmHg vacuum power is used to maximize nuclear purchase for the chopping steps. The Whitestar hyperpulse mode is then activated for the phaco-assisted aspiration of the chopped fragments and epinucleus. For a divide-and-conquer method, sculpting can also be performed with Whitestar.
Second, with Whitestar, 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’s 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 efficient and effective at emulsifying brunescent nuclei. At the 2002 meeting of the American Society of Cataract and Refractive Surgeons, I reported my results using Whitestar to perform phaco chop in 30 consecutive 4+ brunescent cataracts. 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 30 seconds.
The fourth observation is an 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 hyperpulse 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, after treating patients using the Whitestar software, the patients’ corneas seem to be consistently clearer on postoperative day 1. 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.
Dense nuclei offer the greatest test of current phaco technology. Brunescent 4+ lenses challenge surgeons with a poor red reflex and an increased risk of wound burn, endothelial cell loss, and posterior capsule rupture. Although laser phaco and sonics decrease energy and heat delivery, these modalities are ineffective for brunescent nuclei — the very cases for which these advantages are most desired.
In contrast, the Whitestar hyperpulse 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 into the eye; and finally, decreasing the repelling force of the phaco tip lessens the turbulence of nuclear particles in the anterior chamber. These hypotheses need validation from clinical studies.
A cold ultrasound system will permit cataract removal via separate irrigation and aspiration instruments. Such a bimanual phaco technique could be performed through paracentesis-sized incisions (Slides). This, in turn, would create a demand for a paracentesis-insertable IOL technology. In addition to the laser probes, others have experimented with using standard ultrasound with a sleeveless phaco needle for this purpose.8,9 There is always the potential for a significant wound burn using traditional ultrasound. Randall Olson, MD, has been investigating and developing micro-phaco, which is a bimanual ultrasound system using the Whitestar technology.
Besides the prospect of smaller incisions, bimanual phaco may provide additional fluidics advantages. Without any concern with regard to burns, a tighter incision can be used for the phaco tip to minimize leakage along the shaft. 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 may produce a much more efficient, shunt-like flow system that will allow irrigation volumes, ultrasound times, and pump vacuum/flow settings to be reduced.
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- Dodick JM. Laser phacolysis of the human cataractous lens. Dev Ophthalmol. 1991;22:58-64.
- Neubaur CC, Stevens G Jr. Erbium:YAG laser cataract removal: Role of fiber-optic delivery system. J Cataract Refract Surg. 1999;25:514-520.
- Alzner E, Grabner G. Dodick laser phacolysis: Thermal effects. J Cataract Refract Surg. 1999;25:800-803.
- Huetz WW, Eckhardt HB. Photolysis using the Dodick-ARC laser system for cataract surgery. J Cataract Refract Surg. 2001;27:208-212.
- Kanellopoulos AJ, Dodick JM, Brauweiler P, Alzner E. Dodick Photolysis for cataract surgery: Early experience with the Q-switched neodymium:YAG laser in 100 consecutive patients. Ophthalmology. 1999;106:2197-2202.
- Kanellopoulos AJ, et al. A prospective clinical evaluation of 1000 consecutive laser cataract procedures using the Dodick Photolysis neodymium:yttrium-aluminum-garnet system. Ophthalmology. 2001;108:1-6.
- DeBry P, Olson RJ, Crandall AS. Comparison of energy required for phaco-chop and divide and conquer phacoemulsification. J Cataract Refract Surg. 1998;24:689-692.
- Agarwal A, Siraj AA. Phaconit – a 0.9 mm incision phacoemulsification technique. Presented at ASCRS Symposium on Cataract, IOL, and Refractive Surgery. Seattle, Wash; April 1999.
- Tsuneoka H, Shiba T, Takahashi Y. Feasibility of ultrasound cataract surgery with a 1.4 mm incision. J Cataract Refract Surg. 2001;27:934-940.