Efficiency of Torsional Versus Longitudinal Ultrasound

Phacoemulsification of dense, hard lens nuclei generally requires more ultrasound energy than emulsification of softer nuclei. With traditional longitudinal ultrasound, numerous strategies have been developed to reduce the ultrasound energy delivered to the eye, including ultrasound modulation with reduction of on time (ie, duty cycle), increased pulse frequencies, novel phaco tip designs, and optimized fluid dynamics settings.

Many cataract surgeons have adopted torsional ultrasound with the Ozil handpiece (Alcon Laboratories, Inc., Fort Worth, Texas) since its introduction in 2006. The absence of any significant intrinsic repulsion by the side-to-side movement of the phaco tip leads to more efficient emulsification with torsional phaco. The enhanced efficiency is particularly noticeable when emulsifying dense nuclei.

Data are needed to confirm users' clinical impressions of the efficiency with torsional ultrasound. The frequently used parameters of ultrasound time, total energy delivery, or cumulative dissipated energy are unsuitable for comparing two different ultrasound modalities—that would be like comparing apples to pears.

Irrigation fluid use, however, is a clinically valuable and measurable parameter. Fluid use is an indirect indicator of surgical ultrasound use. Additionally, prolonged fluid turbulence through the eye is also potentially harmful to the vitality of corneal endothelial cells, and hence irrigation fluid use is a direct indicator of surgical efficiency as well. In a recent study, torsional ultrasound was associated with less reduction in endothelial cell density.¹

METHODS AND RESULTS
In 2006, we evaluated the efficiency of torsional versus longitudinal ultrasound by comparing fluid use during all stages of cataract surgery. Thirty-two eyes (32 patients) with dense nuclei that were scheduled for cataract surgery were randomly assigned to one of the ultrasound approaches, torsional or longitudinal. Nuclear density was classified from yellow- (grade 2) to red/brown-colored nuclei (grade 4). There were no statistically significant differences between the two groups in nuclear density or age.

One surgeon performed surgery on all eyes with a standard surgical technique (modified divide and conquer fast-crack phaco), identical tips and sleeves (Microsleeve and 45° Kelman tapered tip; both manufactured by Alcon Laboratories, Inc.), and identical fluidics parameters as follows: bottle height was 90 cm during all steps of all procedures; for sculpting, fixed aspiration flow was 20 mL/min, and fixed vacuum was 90 mm Hg; for quadrant removal, fixed aspiration flow was 35 mL/min, and fixed vacuum was 350 mm Hg.

Sixteen cataracts were emulsified with longitudinal ultrasound using the following phaco parameters: for sculpting, linear 100% ultrasound power; for quadrant removal, linear 40% power in pulse mode, with 50% duty cycle, 30 pulses per second. The other 16 cataracts were emulsified with torsional ultrasound, using the following phaco parameters: for sculpting, linear 100% torsional ultrasound amplitude; for quadrant removal, linear 100% continuous amplitude.

With longitudinal ultrasound power, settings that theoretically cause the least repulsion were used to maintain occlusion as much as possible. Ultrasound modulation is not necessary with torsional ultrasound because of the lack of repulsion. Results can be seen in Figure 1 and Table 1.

DISCUSSION
Not surprisingly, fluid use was similar for cortex and viscoelastic removal. During sculpting, the longitudinal ultrasound group needed 47% more irrigation fluid than the torsional group. However, fluid consumption was relatively low in both groups during sculpting compared with the other steps of the procedure.

During quadrant removal, 55% more irrigation was used for longitudinal ultrasound than for torsional ultrasound. The difference was statistically significant. The quadrant removal phase is probably the most important step of the procedure, in which more potential damage can occur to the delicate structures of the eye, particularly the corneal endothelium.

We concluded that torsional ultrasound is significantly more efficient for emulsification of dense nuclei. A potential cause of corneal endothelial cell loss (ie, irrigation fluid use) seems to be reduced with the use of torsional ultrasound technology compared with longitudinal ultrasound, with potentially improved patient outcomes.

Khiun F. Tjia, MD, is an Anterior Segment Specialist at the Isala Clinics, Zwolle, Netherlands. Dr. Tjia is the Co-Chief Medical Editor of CRST Europe. He states that he is a research consultant to Alcon Laboratories, Inc., but that he does not have any financial interest in the products mentioned. Dr. Tjia may be reached at kftjia@planet.nl.

1. Liu Y, Zeng M, Liu X, et al. Torsional mode versus conventional ultrasound mode phacoemulsification: randomized comparative clinical study. J Cataract Refract Surg. 2007;33(2):287-292.