Cataract Surgery, 3rd Edition

PART IV – Phacoemulsification

Chapter 20 – Microcoaxial Phacoemulsification with Torsional Ultrasound

Robert H. Osher, MD

Contents

Cataract surgery has evolved into a very safe outpatient procedure with unprecedented visual outcomes. Yet new technologies continue to emerge that allow the operation to be performed through smaller, less-invasive incisions with more efficient delivery of energy. One method, sleeveless bimanual microphacoemulsification, relies on the separation of irrigation through one port while ultrasound and aspiration functions are utilized through a second incision. Microcoaxial phacoemulsification is another approach in which all functions can be performed through a smaller incision simply by reducing the size of the sleeve. Coupled with surge-reducing fluidic technologies and a new ultrasonic energy delivery modality utilizing an oscillating needle creating torsional side-to-side movement, a highly efficient and extremely safe technology has been achieved. It is the purpose of this chapter to provide the reader with an overview of microcoaxial phacoemulsification and to describe the benefits of torsional ultrasound.

Technological innovations

The INFINITI Vision System (Alcon Surgical Ft. Worth, Texas) introduced the MicroSmooth Ultra Sleeve designed to facilitate coaxial phacoemulsification and implantation of an intraocular lens with a 6mm optic through an unenlarged 2.2mm incision. The thin-walled silicone sleeve (Figure 20-1) with large irrigating ports maximizes irrigation inflow which is necessary for maintaining optimal chamber stability. The sleeve itself provides insulation within the incision, separating the vibrating needle from the surrounding tissue. Its coaxial design also allows the use of aspiration bypass, a thermo-protective safety feature only possible with a coaxial set-up. The same sleeve is used during cortical removal, vacuuming of the capsule, and removal of the ophthalmic viscosurgical device (OVD) at the conclusion of the procedure.

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Laboratory evaluation

Rigorous laboratory investigations were undertaken comparing micro-coaxial performance to that of sleeveless bimanual microphacoemulsification.^[1] Fluidic testing demonstrated that the smaller sleeve reduced the infusion to 75% of that available with a normal sleeve. However, the irrigation flow was considerably higher than the volume available using 19-, 20-, and 21-gauge irrigating choppers, as much as 60% more than the 20-gauge (Figure 20-2). In addition, there was less leakage due to the sealing of the sleeve. These results suggested a fluidic advantage that could provide a deeper chamber with less fluctuation when challenged by either a higher aspiration rate or occlusion break. When this experiment was performed in a test chamber, the results demonstrated greater chamber stability with less surges when using the micro-coaxial system at five different vacuum levels (Table 20-1).

Table 20-1 -- Coaxial set-up produces more stable occlusion break response. Comparison of surge: occlusion-break response.

As incisions get smaller and smaller, temperature within the incision must remain at a safe level in order to avoid thermal injury.^[2] Micro-coaxial phaco has the advantage of an insulating sleeve between the metal of the vibrating needle and the surrounding tissue as well as having the aspiration bypass system. The temperature was measured inside multiple incisions constructed in cadaver eyes. Using a Flir Systems Therma P60 infrared camera (Figure 20-3), a very safe temperature profile was identified. An even greater margin of safety was confirmed by utilizing power modulation with a duty cycle. Moreover, laboratory testing demonstrated an additional temperature reduction with torsional ultrasound.

Incisional competency was also studied since the author had first-hand clinical experience with occasional wound leak using sleeveless bimanual microphacoemulsification. Several histopathologic studies have disclosed collagen damage with the use of a bare phaco tip.^[3,4,5] All laboratory testing of incisional sealing in cadaver eyes showed better incision competency with micro-coaxial phacoemulsification (Figure 20-4).

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Intraocular lens implantation

A final laboratory study was designed to discover a safe and reproducible method of implanting a single-piece AcrySof acrylic intraocular lens (IOL) (Alcon Laboratories) with a 6mm optic through an unenlarged 2.2mm incision. We arrived independently at a very similar technique to that developed by Takayuki Akahoshi, MD, the Japanese surgeon who pioneered this procedure using a sub-2mm incision with NANO Sleeve (Alcon Laboratories). A new injector was designed by Duckworth & Kent (DK 7797) to allow the insertion of the lens using one hand while the second hand introduced an instrument through the stab incision to provide counter-traction. After loading the IOL into the cartridge and folding the lens, using the method shown in the diagram, the chamber and capsular bag were filled with a retentive OVD. The incision was entered with the bevel-down tip of the Monarch C cartridge and counter-traction was applied with an Osher nucleus manipulator (Duckworth & Kent 6-472-2) through a 1mm side-port incision. The cartridge was advanced into the lip of the incision as far as possible without excessive force but not into the chamber. While maintaining counter-traction, the spring-loaded plunger was advanced steadily without hesitation and the leading edge of the lens was delivered into the OVD-filled capsular bag (Figure 20-5). The nucleus manipulator was used to depress the trailing edge of the optic–haptic junction and was then withdrawn from the side-port incision. An Osher dull-fingered Y-hook (Duckworth & Kent MP205) was used to rotate the trailing haptic of the unfolding lens into the capsular bag.

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Clinical evaluation

The author designed a prospective clinical study to evaluate microcoaxial phacoemulsification in which 100 consecutive patients undergoing routine cataract surgery were enrolled.^[6]All eyes were demonstrated to have consistent chamber stability and incisional competency. All phacoemulsifications were uncomplicated with no special instrumentation required, except for a 2.2mm diamond keratome. The only machine parameter that required modification was the bottle height, which was increased from 45 cm to 70 cm. Otherwise, the phacoemulsification was identical to the author's preferred slow-motion divide and chop technique. The IOL was injected using the one-handed counter-traction technique. In contrast to the phacoemulsification, the IOL insertion was initially challenging until the counter-traction method was mastered then all difficulties vanished. The closure was sutureless in all but the very last patient, whose incision was the only one that leaked until a 10-0 nylon suture was passed. The surgeon found that stromal hydration was more effective when performed before the OVD was removed (Figure 20-6).

Intraoperative and postoperative complications were absent and the patients consistently experienced excellent uncorrected vision on the first postoperative day. The details of the laboratory and clinical studies have been published in the 2007 Journal of Cataract and Refractive Surgery.^[1,][6]

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Torsional ultrasound and microcoaxial phacoemulsification

Traditional longitudinal phacoemulsification developed by Charles Kelman, MD, utilizing a forward and back “jackhammer” effect has remained relatively unchanged for more than 3 decades. Improved handpieces, instrumentation, and surgical techniques have certainly been introduced, along with other machine innovations, such as continuous irrigation, surgeon control of parameters, and power modulation, using the concept of duty cycle to enhance efficiency while reducing temperature within the incision. Yet, the basic principle of emulsifying the nucleus with longitudinal ultrasound has never been modified. As the nucleus is removed, there is some degree of repulsion and thermal friction within the incision followed by retraction of the tip that creates cavitational energy and free radicals.

In early 2006, Alcon introduced a new concept, OZIL; an option of torsional ultrasound on the Infiniti Vision System. A dedicated handpiece which utilized an angled or curved tip would ultrasonically oscillate from side-to-side creating a more efficient emulsification with less friction-generated heat within the incision (Figure 20-7). The oscillatory motion of the hub occurred at a frequency of 32,000 Hz creating an equivalent stroke at the tip of approximately 90μ at 100% power, similar to traditional phacoemulsification. However, unlike longitudinal stroke, the torsional stroke decreases away from the tip so there is significantly less movement within the incision (e.g. 30μ at 100%).

The effect of this modification of ultrasound is quite profound. First, cutting efficiency is greatly increased. Traditional ultrasound is only 50% effective because the backwards motion of the stroke does not contact lens material. Rather than cutting only 50% of the time when the tip is moving forward, nuclear material is being emulsified or sheared constantly with torsional ultrasound, as the tip is moving in both directions.

Second, the behavior of the nuclear material is quite different because there is no repulsion and chasing after pieces is unnecessary. There is visibly less chatter and dispersion of lens material versus traditional longitudinal ultrasound. The ability to maintain nuclear material at the tip is increased and turbulence is reduced.

Third, there is an improved thermal safety profile. The primary source of heat is friction and, because there is less movement in the incision, the heat that would normally be produced from traditional phaco is reduced by approximately two-thirds given the same power level.^[7] Operating at the lower frequency of 32 KHz versus 40 KHz also has a thermal benefit and an energy saving of 20%. Power modulation can also be used with various duty cycles further improving the thermal safety profile. Coupled with the insulation of the silicone sleeve and the presence of aspiration bypass, there is even more thermal protection with the reduced incision size.

It should be emphasized that the surgeon may individualize the torsional settings. Torsional ultrasound can be combined with longitudinal ultrasound (sequential not simultaneous) in different ratios selected by the surgeon, which is a very effective approach to the harder nucleus (Figure 20-8). The ability to program the traditional duty cycle into the energy delivery equation also has been an important development. As a result, surgeons trying this new technology have found that the emulsification requires less cumulative energy and machine fluidic parameters can be reduced. In a laboratory study using small silicone beads suspended in balanced salt solution in cadaver eyes, torsional ultrasound resulted in better fluidics with much less repulsion.^[8] It was possible to achieve the same efficiency with lower fluidic parameters. In a randomized comparative clinical study involving 525 eyes undergoing phacoemulsification with either conventional or torsional ultrasound, results showed that the torsional mode produced more effective lens removal and a smaller amount of phaco time and energy.^[9]

One challenge that is being addressed is the requirement to use the curved Kelman-style tip in order to reap the benefits of this new technology. While it is possible to emulsify the nucleus using torsional ultrasound with a straight tip, intermittent bursts of longitudinal ultrasound are necessary to prevent “apple coring” of the nucleus. Since it has been estimated that 80% of the world's phaco surgeons use a straight tip, there is a need for a less curved design that would be easier to use than the traditional 30° curve of the Kelman tip (Figure 20-9). Dr. Akahoshi in Japan and Dr. Osher in the United States have independently arrived at a blended tip with a curve of approximately 12°, which shares similar efficiency and thermal benefits as the more angled Kelman tip. While Dr. Akahoshi prefers a square configuration on his tip and Dr. Osher prefers a 30° round tip, a variety of tip options and innovations are likely to appear in the future.

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Conclusion

Favorable results strongly suggest that these new technologies will be explored and expanded upon by many ophthalmologists.^[1,][5,][6] In the author's personal opinion, microcoaxial phacoemulsification with torsional ultrasound is a lovely marriage that should endure the test of time.

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References

[1]. Osher R.H., Injev V.P.: Microcoaxial phacoemulsification Part 1: Laboratory studies. J Cataract Refract Surg 2007; 33(3):401-407.

[2]. Osher R.H., Injev V.P.: Thermal study of bare tips with various system parameters and incision sizes. J Cataract Refract Surg 2006; 32:867-872.

[3]. Vasavada A.R.: Phaco tips and corneal tissue: histomorphology and immunohistochemistry reveal the effects of sleeveless and sleeved tips. Cataract & Refractive Surgery Today 2005; June(Suppl.):9-10.

[4]. Weikert M.P., Koch D.D.: Phaco wound study: alterations in corneal wound architecture with bimanual microincisional phacoemulsification. Cataract & Refractive Surgery Today 2005; June(suppl):11-13.

[5]. Berdahl J.P., DeStafeno J.J., Kim T.: Corneal wound architecture and integrity after phacoemulsification. Evaluation of coaxial micro incision and micro incision bimanual technique. J Cataract Refract Surg 2007; 33:510-515.

[6]. Osher R.H.: Microcoaxial phacoemulsification Part 2: Clinical study. J Cataract Refract Surg 2007; 33:408-412.

[7]. Boukhny M.: Laboratory performance comparison between torsional and conventional longitudinal phacoemulsification, 2006. Presented at ASCRS, Session 1-G

[8]. Solomon K.: Alcon CME Program, 2006. American Academy of Ophthalmology

[9]. Liu Y., Zeng M., Liu X., Luo L., Yuan Z., Xia Y., et al: Torsional mode versus conventional ultrasound mode phacoemulsification: Randomized comparative clinical study. J Cataract Refract Surg 2007; 33:287-292.