As the fields of cataract and refractive surgery increasingly merge, and modalities from both fields are utilized in one another, we see that there is increasing interest in decreasing the invasiveness of lens-related surgical modalities. We are seeing enormous expansions in phacoemulsification technologies that are resulting in less invasive surgery and more rapid and excellent visual rehabilitation. This article discusses some of the systems that we are currently investigating.
The NeoSoniXTM system from Alcon Surgical (Fort Worth, TX) uses classic ultrasound combined with oscillatory motions up to 2&Mac251; in arc. The oscillatory frequency is in the sonic range (not ultrasonic), and vibrates at 120 Hz. It combines the to and fro ultrasonic vibration of the tip with up to 2&Mac251; in arc. You can also fractionate to lower levels of oscillation than 2&Mac251; at 120 Hz. This gives you the ability to address nuclear material with not only the back and forth vibratory motion of the tip, but also a twisting motion that behaves in a way analogous to an apple core, twisting as it pushes to achieve a better cut. Also, in association with the NeoSoniXTM technology there is new software on the Alcon 20000® Legacy® system, called Advantix software. It has many new options, such as Inclusion Mode phaco, which allows you to change all of your parameters of ultrasound power percentage and aspiration flow rate going from an unoccluded tip to an occluded tip. It has enormous options. It also has mode sequencing, which allows you to go from one step to another with a movement of the foot pedal. It has a special Viscoelastic Mode, which gives you a slight pause in the onset of power until flow and aspiration begin to clear some of the viscoelastic. A great advantage of the NeoSoniXTM Oscillatory Mode is that it doesn't create heat at all, it's additive to the ultrasonic vibrations of the tip. You can program the percentage of power of which you want to begin oscillations from zero all the way up to 100, and it doesn't create cavitational energy or free radicals. So in a sense you're almost getting something for nothing.
The Staar system is called Sonic Wave, and combines both ultrasound phacoemulsification and sonic phacoemulsification. Ultrasound phacoemulsification involves vibratory frequencies of the tip, between 26 and perhaps as high as 60 kHz. Sonic phacoemulsification involves vibratory frequencies between 20 and 400 Hz, so there is a difference of 1,000 Hz. The vibratory frequencies at ultrasound range create intramolecular friction forces that are transmitted to the tissues as heat. The sonic is independent of friction forces; you can take the sonic tip and hold it in your bare hand while it's vibrating. Its cool temperature eliminates the potential for thermal injuries to tissues. The sonic is also capable of addressing very hard nuclei, so you obtain good cutting ability and no heat, which is a great advantage. Another advantage of the Sonic Wave is that the aspiration tubing is tightly coiled, which necessitates a continuous change in the direction of the column of fluid. At high flow rates, this translates into high resistance to flow, which minimizes surge dramatically. So this system is capable of so-called “cold” phaco, it will address all levels of cataract, and within the same system you have the ability to go back and forth with a kick of a foot pedal between sonic and ultrasonic, so if the tip gets clouded in sonic mode, you push the pedal to the right and you're in ultrasound. I've probably done 750 cases with the Staar system.
This new technology from Allergan involves further modulations in power so that the Burst Mode and Pulse Mode, which were the initial power modulations, can be altered in such a way that the power is not on for the full pulse or the full burst. It shortens the duration for which the energy is on to be faster than the threshold for tissue response to thermal energy. It's still a cold phaco emulsification technique, and yet it is capable of addressing very hard cataracts. And because it is cold, it also offers the option of performing cataract surgery through two stab incisions, reducing the incisions through which a cataract is taken out to less than 1 mm. That will be very important once we get injectable materials that can be inserted through that same small size incision.
I am an investigator for the new Asclepion–Meditec Phacolase system and the Paradigm laser photon system, and I'm very impressed with their early results and the potential for future clinical applications as these technologies evolve. However, at this time, sonic and ultrasonic phacoemulsification with power modulations work best for dense nuclei. I produced an article in the February issue of the Journal of Cataract and Refractive Surgery, along with my associates, Drs. Richard Hoffman and Mark Packer, called “The Use of Power Modulations in Phacoemulsification,” which showed that utilizing power modulations in conjunction with high flow and high vacuum levels can minimize the amount of energy going into the eye. We use mechanical forces in the form of chopping to disassemble the nucleus, and vacuum forces aided by bursts or pulses of phaco energy to extract nuclear material, rather than using phaco energy to emulsify from within the eye. In using six different machines we were able to dramatically reduce the amount of energy going into the eye, and we were able to document, using 244 consecutive cases, that the clarity of the cornea in the immediate postoperative period was exceptional due to decreased energy levels. The immediate postoperative uncorrected visual acuity between 2 and 24 hours was inversely proportional to energy; that is to say, in decreasing effective phaco times we got increasing excellence in immediate postoperative uncorrected visual acuities. Abhay Vasavada, MD from Ahmedabad Guj, India has recently shown that independent of the viscoelastic used, intraocular pressure spikes in the postoperative period are directly related to the effective phaco time. This is probably due to the fact that the cavitational and other energy from the phaco tip creates trabeculitis, and lowering the effective phaco time reduces the incidence of inflammation in the trabecular meshwork. Ten years ago, the promise of lower energy in the form of laser surgery was very appealing. However, as we've developed the technology for classic ultrasound and improved it with power modulations, we've reduced the energy into the eye equal to or lower than that delivered by lasers.
There are a couple of additional systems out there. Endocapsular vortex emulsification is a system being developed by Bausch & Lomb for which I am an investigator. Currently in its investigational stage, this system uses a high-speed rotary impeller through a 1 mm capsulorhexis to create vortex flow within the capsular bag, dramatically expanding the bag. The impeller, which rotates at about 60,000 cycles per minute, not only chews up the cataract but also draws it to the tip. All of the action, including the flow, is limited to the capsular bag—there's nothing entering the AC, so it totally protects the cornea. It's also capable of grinding up pretty dense nuclei, at least in the laboratory and in animal eyes (we have yet to address humans with that system), but it looks very promising. It is also a very low-skill modality; you just stick it through the capsulorhexis, advance the impellers, turn the motor on, and just hold it still—it doesn't require intraocular manipulation. The other thing that's interesting about endocapsular vortex emulsification is that it not only gets rid of the cataract but it also strips the cortex. It will of course require opening that 1 mm capsulotomy in order to insert a traditional implant, or else the development if an injectable system, and then we will be able to take full advantage of the technology.
Finally, there is an AquaLase system that Alcon is developing which uses pulsed warm water to dissolve cataractous material. Mark Andrews, MD, from Wills Eye Hospital is developing the system. According to Dr. Andrews, one of its major advantages is that it not only dissolves and aspirates the cataract, but it kills the lens epithelial cells in the fornix of the capsule so theoretically at least, we would never have posterior capsular pacification and we could do away with the YAG laser. We'll have to wait for the system's developments in clinical trials.I. Howard Fine, MD, is a founding partner of the Oregon Eye Associates in Eugene, Oregon, as well as President of the American Society of Cataract and Refractive Surgery. Dr. Fine is a clinical investigator for all systems discussed. He is not a paid consultant for any of the companies mentioned. (541) 687-2110; firstname.lastname@example.org