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Up Front | Sep 2007

Torsional Ultrasound: What is its Impact After 1 Year on the Market?

I expect that modern phaco machines will soon switch to a nonlongitudinal ultrasound modality.

Torsional ultrasound was introduced in the first half of 2006, when the OZil handpiece (Alcon Laboratories, Inc., Fort Worth, Texas) was unveiled as a new component of the Infiniti Vision System phacoemulsification machine (Alcon Laboratories, Inc.). This ultrasound technology has been marketed worldwide, and numerous presentations, articles, and live surgery demonstrations have shown its potential benefits.

In its earliest stages, I indicated that torsional ultrasound would revolutionize cataract surgery and become the new standard of phacoemulsification technology in the near future.

MARKET PENETRATION
In the second quarter of 2007, 60% of all phaco machines sold worldwide were Infiniti machines. For every 100 Infiniti systems currently sold, approximately 98 are equipped with OZil handpieces (Figure 1). In the same quarter just 2 years prior, 50% of all phaco machines sold were Infiniti systems. The 10% increase in sales is undoubtedly due to the introduction of torsional ultrasound.

The immediate acceptance of torsional ultrasound is, indeed, striking. As I can attest due to my hands-on experience during initial investigations of the Infiniti machine with OZil technology, torsional ultrasound is convincing. Surgeons immediately feel the difference between traditional and torsional ultrasound (Table 1).

WHAT MAKES IT SUPERIOR TO TRADITIONAL ULTRASOUND?
The key element of torsional is its effective transverse motion at the end of the phaco tip. It does not cause significant repulsion, and friction is greatly reduced inside the tunnel incision. Both have been clarified extensively.

The absence of noticeable repulsive action of the tip leads to a completely new approach to fluidics and ultrasound power settings. With traditional ultrasound, settings were modulated to mitigate the repulsion induced by the longitudinal movement of the phaco tip. Either ultrasound settings had to be limited in power, or the surgeon had to pause between pulses/ bursts to let lens fragments come back into contact with the tip. There was always a drive toward higher vacuum and aspiration flow settings to compensate for the same repulsive effect of traditional ultrasound. Anterior chamber instability and high fluid turbulence are two potential negative consequences of higher fluidics settings.

Torsional ultrasound, however, does not require very high vacuum and flow to keep the lens material close to the phaco tip. Emulsification is still extremely efficient with moderate vacuum and flow settings. Fluid turbulence is lower, and consequently, endothelial cells are better protected. Anterior chamber stability can be almost absolute, and the risk of posterior capsules jumping into the phaco tip is minimized. A high torsional ultrasound power in continuous mode is feasible. In fact, it is the most efficient and fastest way to emulsify cataracts.

The only reason to mix longitudinal ultrasound bursts with torsional ultrasound is to prevent clogging of flared phaco tip types. Their funnel shape may become obstructed by denser nuclear material that has not been completely emulsified by torsional ultrasound.

Both tapered and micro tips, however, rarely clog. In my opinion, the continuous torsional ultrasound mode is the best option when using these tips.

WHEN TORSIONAL IS MOST BENEFICIAL
In all cases when aspiration and irrigation flow are restricted, torsional ultrasound is significantly more efficient compared with traditional ultrasound. When using traditional ultrasound with lower flow and vacuum settings, repulsion of nuclear fragments becomes more prominent. This may lead to difficult manipulations inside the eye and a greatly increased risk for complications. Below is a list of two categories where the highest benefit of torsional ultrasound is revealed.

Microcoaxial and bimanual phaco. Both procedures have limited irrigation flow capacities, and therefore aspiration flow settings must be lowered accordingly. With traditional ultrasound, the efficiency of emulsification decreases, and the procedure time increases. When I switched from 2.6-mm traditional coaxial phaco to 2.2-mm microcoaxial torsional phaco, my net surgery time decreased. I can now perform more microcoaxial torsional procedures per session, compared with my previous traditional coaxial cases.1

Challenging or complicated cases. It is more beneficial to use torsional ultrasound during such instances as zonulolysis, floppy iris syndrome, or posterior capsular rupture. A high aspiration flow will attract vitreous and/or floppy irides into the tip, and the risk for severe complications is high. A low fluidics strategy is therefore mandatory for these challenging situations. Torsional ultrasound is a superb innovation for these otherwise very worrying cases. My patient outcomes in many difficult situations have been satisfactory since the use of OZil technology.2

MACHINE SETTING CHANGES
In the traditional ultrasound era, surgeons and industry searched for improvements in ultrasound hardware and software, tried to manufacture better lower compliance tubing, and designed new phaco tips and sleeves. All changes were targeted at increasing vacuum and flow to improve the efficiency of phacoemulsification. Many of my colleagues were involved in the rat race to achieve higher—not to mention the highest—fluidics settings.

But, torsional ultrasound has induced a paradigm shift in fluidics parameters settings.

Vacuum and aspiration flow should be lowered to moderate levels, thus creating a high margin of safety. Additionally, low-to-medium vacuum settings minimize the occlusion break response. This results in extremely stable anterior chambers and reduces the possibility of inadvertent posterior capsule ruptures.

Low aspiration flow during torsional ultrasound induces low turbulence in the anterior chamber, and the protective viscoelastic is not evacuated precociously. Corneal endothelial cells are better preserved, and patient outcomes are more favorable. Torsional ultrasound also makes cataract surgery training easier and safer for residents. The higher safety margins help build confidence in resident, teacher, and patient.

CONCLUSION
I think that we may already conclude from this year's market development and surgeon's feedback worldwide that torsional ultrasound is the new standard of care in phacoemulsification equipment. Friends and foes agree upon the superiority of the technology, and I expect that all modern phacoemulsification machines will switch to some kind of nonlongitudinal ultrasound modality in the future.

Khiun F. Tjia, MD, is an Anterior Segment Specialist at the Isala Clinics, in Zwolle, Netherlands, and an Associate Clinical Professor affiliated with the University of Groningen, in the Netherlands. Dr. Tjia is the Co-Chief Medical Editor of CRST Europe. He states that he is a research consultant for Alcon Laboratories, Inc. Dr. Tjia may be reached at kftjia@planet.nl.

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