Education Forum Recap
Fine-tuning Cold Phaco
Here's how WhiteStar technology is making cataract removal more efficient than ever before.
Randall J. Olson, M.D.: We've made quite a few advances in cold phaco, particularly in energy efficiency, followability and temperature regulation. How has WhiteStar technology contributed to these improvements?
William J. Fishkind, M.D.: WhiteStar addresses two very important cold phaco trends. We're improving the delivery of ultrasonic energy to the anterior segment, which in turn, decreases the amount and duration of power delivered to the eye.
Olson: The worst action we can take during phaco is delivering too much ultrasound energy. You don't even have to touch the cornea to create problems. If you get close enough to the cornea with ultrasound emanating from the tip, you'll destroy endothelial cells.
How does WhiteStar use ultrasound to cut the nucleus without delivering excess power to the eye?
Fishkind: We're all familiar with jackhammer and cavitational effects. Specifically, jackhammer is useful for breaking the nucleus into small fragments. Cavitation, usually divided into transient and sustained, is the energy that emulsifies lens fragments.
Initially, continuous ultrasound power delivers transient cavitation, which breaks the nuclear bonds to create emulsate. Sustained cavitation occurs after transient cavitation, when the energy becomes less focused and less powerful, and emulsifies the nucleus less effectively.
Continuous power is useful for divide-and-conquer procedures. Once the nucleus breaks into fragments, you can emulsify them by switching from continuous to ultra-pulse modality. WhiteStar has such short on-off cycles that it maximizes transient cavitation and becomes an effective emulsifying force, especially when the nucleus is in fragments. Ultimately, we're delivering less ultrasonic energy to the eye.
Improved clinical outcome
Olson: How does decreased energy affect clinical outcomes?
Advantages of Variable WhiteStar
Fishkind: My colleagues and I randomized 97 cataract patients to receive treatment with standard Sovereign® or Sovereign® with WhiteStar technology. Pooled results showed that WhiteStar patients were exposed to 25% less effective phaco power and 26% less mean ultrasound power. Our most important finding, however, was that 3 months after surgery, WhiteStar patients had 26% less endothelial cell loss than their counterparts treated with standard Sovereign®.*
Lisa B. Arbisser, M.D.: I've had similar results with my patients. Ninety-eight percent of my eyes are 20/40 or better on the first postsurgical day, and I have no corneal edema, even if the patient has brunescent lenses.
Customizing duty cycles
Olson: I really appreciate the zero incidence of wound burn with WhiteStar. In tests, I've occluded the aspiration line while keeping the phaco needle at 100% power (WhiteStar CF). If you're using continuous ultrasound where no fluid is flowing back to the phaco needle, you can go from a normal temperature to wound burn in a couple of seconds. With WhiteStar, the temperature never rose above 32º C, even after 3 minutes of continuous running.
We can attribute this excellent temperature control to WhiteStar techology's duty cycle, or the relationship between off-time and on-time. I understand that Sovereign® with Variable WhiteStar 6.0 lets us change linear phaco power and customize the duty cycle to our specific needs.
With Variable WhiteStar I can adapt my technique for different stages of cataract removal.
-- Lisa B. Arbisser, M.D.
Arbisser: I like to explain this new feature with an automobile analogy. In a car, the gas pedal controls the engine speed or RPMs. As you depress the accelerator, the engine revs, making the car move faster. Traditional phaco works on the same principle, allowing you to adjust phaco power linearly.
Variable WhiteStar also lets you move among the four basic phaco modes of continuous, pulse, power pulse and burst, but instead of setting two WhiteStar levels (occluded and unoccluded), you can set four double levels. To continue my car analogy, the duty cycle is like the car's gears. The more "on" you have relative to "off," the more efficient the gears. When I'm working on a very dense cataract, I can stay at 20%, which pops up to 33% when the phaco tip occludes, and then the next level down I can use 33% popping up to 43%. With Variable WhiteStar, the foot pedal controls phaco power and duty cycles simultaneously, so I can adapt my technique for different stages of cataract removal.
Olson: One advantage of setting a long duty cycle or long off interval with Variable WhiteStar is improved followability. Fragments stay near the tip and are emulsified with minimal energy. Less energy means less repulsive force and, consequently, less micro-chatter. I think that using a long duty cycle will improve followability and decrease how much energy we use.
Temperature control and microphaco
Olson: I'm a strong advocate of microphaco and using WhiteStar for microphaco because this technology has never produced a wound burn. If we can use ultrasound without worrying about wound burns we can have all the power of WhiteStar -- decreased energy, improved followability -- and still operate through a 1-mm incision with a bare 21-gauge needle.
What's your experience been with microphaco?
Fishkind: When we started working with microphaco, we had to overcome some hurdles. We had the phaco machine, but we didn't know how to match incisions and needles and second instruments. Now, we have stabilized systems to help us, including advanced fluidics, which decrease the tendency for surge in bimanual phaco.
Olson: Microphaco is an exciting trend, and as lenses catch up to the procedure, microphaco will be the next big wave.
Arbisser: Microphaco doesn't work with continuous ultrasound, but that's OK. Continuous phaco isn't necessary or appropriate. I recommend using WhiteStar technology's burst, pulse and hyper-pulse options to tailor your surgeries, making the most of the ultrasound you use. Our next step will be improving aspiration so we can perform phaco-assisted aspiration rather than phacoemulsification with surgery.
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*Paper presented at the ASCRS meeting in Philadelphia, June 2002.