1.1Micro-Coaxial Phacoemulsification with Torsional Ultrasound

James M. Osher and Robert H. Osher

Core Message

ßMicro-coaxial phacoemulsification with torsional ultrasound is an exciting new technol-

ogy that allows the surgeon to remove the cataract through a smaller incision with enhanced safety and efficiency.

1.1.1 Introduction

Cataract surgeons continue to explore new technologies that improve safety, efficiency and patient outcomes. Two approaches, bimanual microphacoemulsification (B-MICS) and micro-coaxial phacoemulsification (C-MICS), have allowed surgeons to operate through smaller incisions. Bimanual MICS utilizes a sleeveless tip and requires two small incisions approximately 1.0– 1.5mm in length, one for irrigation and chopping and the other for ultrasound and aspiration. Micro-coaxial phacoemulsification is a sleeved procedure allowing ultrasound, irrigation, and aspiration to be performed through a single incision approximately 2mm in length.

R. H. Osher (*)

Department of Ophthalmology, University of Cincinnati and

the Cincinnati Eye Institute Cincinnati, Ohio USA

e-mail: RHOsher@CincinnatiEye.com

Another recent innovation in phaco technology is torsional ultrasound. Instead of the traditional jackhammer movement of longitudinal ultrasound, the torsional needle creates a side-to-side oscillatory movement, which has been proven to be more efficient with less chatter and repulsion of nuclear fragments. This chapter will review the benefits of combining micro-coaxial phacoemulsification with torsional ultrasound.

1.1.2Micro-Coaxial Phacoemulsification

Micro-coaxial phacoemulsification was developed by Alcon in 2003 for the purpose of providing several advantages over the conventional coaxial and bimanual techniques. By introducing the smaller Ultra sleeve designed to be used with the Infiniti Vision System, it became possible to remove the cataract and implant a full-size intraocular lens (IOL) through an unenlarged 2.2 mm incision. Conventional coaxial phacoemulsification uses a 2.75–3.0 mm incision. By decreasing incision size to 2.2 mm, surgeons observed less induced astigmatism. One study found that a 3.0 mm incision induces a third to a half diopter of astigmatism, while a 2.2 mm incision approaches toric neutrality [1]. Decreasing surgically induced astigmatism has become essential as presbyopia-correcting lenses and toric lenses have gained widespread acceptance, while patient expectations for uncorrected vision have never been higher. When compared to bimanual microphacoemulsification, micro-coaxial technique has been reported to provide superior fluidics and less incisional leakage, leading to better chamber stability [2]. While the smaller sleeve used in the micro-coaxial procedure results in a 25% decrease in infusion when compared

to the standard sleeve, the irrigation flow is considerably higher when compared to the volume available using 19, 20, and 21 gauge irrigating choppers. In fact, the Ultra sleeve provides as much as 60% more flow than a variety of 20-gauge irrigating choppers used in bimanual phaco [2]. The micro-coaxial surgeon has the option to access higher fluidic settings since there is no need to compensate for the limited irrigation inherent in the B-MICS procedure.

Another advantage of micro-coaxial phaco is enhanced thermal protection. Micro-coaxial phaco uses an insulating sleeve between the vibrating needle and the tissue bordering the incision. C-MICS also takes advantage of the aspiration bypass system (ABS) which is not possible with the bare needle of bimanual phaco. Several studies have suggested that the thermal profile of micro-coaxial phaco has a greater margin of safety [2–5]. When coupled with torsional ultrasound, which creates even less friction in the incision, the potential for thermal damage is substantially reduced.

A third advantage of micro-coaxial phaco involves the architectural integrity of the incision. As a general rule, a smaller incision size reduces the possibility of leakage and improves wound sealability. However, while B-MICS incisions are smaller, laboratory and clinical evidence has been published which shows a greater disruption in wound architecture when compared to micro-coaxial incisions [6–8]. Spontaneous wound leakage and India ink penetration was present in all eyes that underwent the bimanual technique but was not seen in the micro-coaxial group [6]. These authors also found more qualitative trauma to Descemet’s membrane and to the corneal endothelium as demonstrated by scanning electron microscopy (SEM). A randomized clinical trial was designed to compare the ocular surface fluid ingress into the anterior chamber after cortical removal and at the end of the procedure using trypan blue as the quantifying tracer. At both points, trypan blue ingress was statistically significantly higher in the bimanual group than in the micro-coaxial group [9]. A histomorphological and immunofluorescence study in rabbits comparing bimanual and coaxial phaco demonstrated that B-MICS resulted in more disorganized collagen fibrils, excessive shrinking of stromal fibers, and more ragged tunnel margins [10, 11].

Integrity of the incision is not only important in preventing aqueous from exiting the eye, but it is also crucial in preventing bacteria from entering the eye [12]. Studies have shown that the short length and single plane of the incision in bimanual phaco may allow an increased

ingress of bacteria [13, 14]. Another study based on finite analysis concluded that less incision stress is created with the micro-coaxial incision [15]. A clinical study evaluating 2.2mm incisions using a square configuration popularized by Paul Ernst et al. [16] found no evidence of either hypotony or wound leakage [17]. One of the authors (RHO) of this chapter has not seen a postoperative complication related to the 2.2mm incision since beginning micro-coaxial phacoemulsification in 2003.

Another advantage of micro-coaxial phaco is related to the smaller dimensions of the actual instrumentation. Better visualization when the pupil is small has been reported [18] and we have found that the emulsification is easier to perform in small eyes with shallow anterior chambers.

In the United States, where a micro-incisional IOL is not yet approved, the 2.2 mm incision of microcoaxial phaco permits implantation of a full size, high quality optic without either an enlarged or separate incision. Several injectors requiring either a one hand or a bimanual insertion technique are able to consistently and gently deposit the IOL into the capsular bag regardless of whether the surgeon selects an AcrySof IQ, Toric, or ReStor IOL. Either the C cartridge or the smaller D cartridge manufactured by Alcon is available at the present time.

It has been surprisingly easy to transition to microcoaxial phacoemulsification with minimal change in instrumentation and technique. Leading American educators like Richard Lindstrom, have also found that it is an easier operation to teach than B-MICS. The cataract surgeon who authored the peer-reviewed pilot study on micro-coaxial phacoemulsification found that the actual lens removal was no more difficult than performing traditional phaco. However, he did conclude that a learning curve was necessary for the IOL insertion, but with experience, this surgeon was able to achieve safe and reproducible IOL implantation [19]. The same study demonstrated a low incidence of intraoperative and postoperative complications with excellent clinical outcomes.

1.1.3 Torsional Ultrasound

Traditional longitudinal phacoemulsification was developed by Charles Kelman more than four decades ago and has remained relatively unchanged. Certainly, there have been improvements in techniques, instrumentation, and hand-piece design, as well as machine

engineering. However, the basic principle of emulsifying the nucleus with longitudinal ultrasound has not undergone any major modification. At the annual meeting of the European Society of Cataract and Refractive Surgery in 2005, Alcon introduced OZil, a new platform providing torsional ultrasound on the Infiniti Vision System. While longitudinal phaco produces a jackhammer motion in which emulsification is only taking place 50% of the time, the side-to-side oscillatory movement of torsional ultrasound results in shearing and cutting 100% of the time. Because the entire stroke is utilized, torsional ultrasound is significantly more efficient than conventional ultrasound. Moreover, surgeons have the option of lowering fluidic parameters to safer levels without compromising efficiency.

The advantages of torsional phaco have been well documented. Torsional ultrasound causes less repulsion of nuclear material [20], and is best illustrated by the high-speed cinematography in a video produced by Teruyuki Miyoshi and Hironori Yoshida which won the Grand Prize at the 2007 ASCRS and ESCRS film festivals [21]. Another study found reduced turbulence with torsional vs. longitudinal phaco [22]. In a cadaver study comparing torsional ultrasound to conventional ultrasound, a high-speed camera was used to follow implanted micro-carrier beads [23]. Because there was little or no repulsion of the beads when using torsional fluidics, the removal time was 50% less with torsional ultrasound. The significance of less repulsion was implied in another award winning video from the 2008 ASCRS Film Festival by Osher and Osher, demonstrating that nuclear fragments were more easily displaced posteriorly through a tear in the posterior capsule with longitudinal rather than torsional ultrasound [24].

Torsional ultrasound has also been shown to increase the efficiency of the phacoemulsification. Simulated cataracts using a hard polymer were emulsified comparing cutting efficiency. While conventional phaco required 1.63 oz of force to cut through the cataract model, torsional ultrasound required 0.86 oz of force [25]. One investigator found a 23% reduction in BSS with torsional phaco compared to longitudinal, and lower vacuum levels appeared to achieve similar efficiency [26]. Less BSS fluid was required using torsional ultrasound in another series [27]. A European study compared fluid use during different stages of the emulsification. During quadrant removal the longitudinal ultrasound group required 55% more irrigation fluid than the torsional group [28]. The author concluded that torsional ultrasound was more efficient for dense nuclei

and provided greater safety to the corneal epithelium. A Chinese study compared torsional vs. traditional ultrasound in a randomized comparative clinical study [29]. Both ultrasound time and cumulative dissipated energy proved less in the torsional group for all grades of cataract. Corneal edema, Descemet’s striae, and a higher endothelial cell loss were found in the traditional ultrasound group. Best corrected visual acuity was better in the torsional group at days one and seven, although there was no difference between groups at the 1 month postoperative visit. Another European study showed faster removal times and lower energy exposure at the incision with torsional ultrasound [30]. Tip travel was investigated and found to be less with torsional ultrasound [31]. The author concluded that a shorter cumulative tip travel and less procedure time indicated improved efficiency and safety.

Torsional ultrasound generates less heat than longitudinal ultrasound due to several factors. One reason is that the frequency of OZil has been reduced from 40 to 32 kHz. In one study, torsional ultrasound was associated with a 60% reduction in temperature rise within the incision compared to longitudinal ultrasound [32]. Since longitudinal ultrasound at 100% power generates a linear stroke of 90 μm, the lateral movement of the tip is also about 90 μm. However, the angled tip used with torsional ultrasound creates a rotational movement of the shaft measuring only 40 μm. Therefore, movement of the tip within the incision with torsional ultrasound is less than half the movement characteristic of traditional phaco. When combined with the fact that the tip oscillates at a lower frequency, the heat reduction due to less frictional movement against the tissue adjacent to the incision, is approximately one-third that of longitudinal phaco [33].

One of the few perceived disadvantages of this new technology is that the surgeon is required to use a curved tip to realize the full benefits of torsional ultrasound. While it is possible to emulsify a nucleus using a straight tip with torsional ultrasound, bursts of longitudinal energy are necessary to prevent “apple-coring” of the nucleus. The 22° curvature of the Kelman tip has appealed to some, but not to all surgeons. Since the majority of cataract surgeons around the world prefer a straight phaco tip, Dr. Takayuki Akahoshi from Japan and Dr. Robert Osher independently designed a modified tip with a 12° curvature that shares high efficiency and thermal benefits similar to the Kelman tip. In addition, this new 12° tip has the opening on the same side as the curve, allowing the surgeon to embed the tip in

the lens without disturbing the overlying OVD, sculpt more safely, and chop more efficiently. One investigator found that the OZil 12 tip geometry translates to 50% reduction of stroke within the incision compared to traditional phaco, and a two-thirds reduction in thermal energy compared to longitudinal ultrasound [34]. In a study comparing the OZil 12 to the Kelman tip, the authors found that the clinical performance was equally effective [35]. Alcon has developed a complete line of tips to allow the surgeon to choose the size and configuration of the tip that he or she prefers.

While comments in this chapter reflect the author’s experience with the Alcon technology, other companies are introducing microincisional technology such as Bausch & Lomb’s Stellaris. Alternatives to traditional longitudinal phaco such as AMO’s elliptical transverse ultrasound are also being introduced by industry.

1.1.4Our Procedure for Emulsifying the Nucleus

After the capsulorhexis has been performed, the nucleus is loosened by hydrodelineation and the cortex is loosened by hydrodissection. The anterior chamber is filled with Healon5. The bevel-down OZil 12° tip is placed into the central anterior cortex where, a divot is removed to assure fluid exchange at the tip (Fig. 1.1). The tip is rotated 180° until bevel up and the parameters are reduced (slow motion phaco [36]) during the sculpting of the troth (Fig. 1.2 ). A nuclear chopper is introduced through the stab incision and the nucleus is divided into hemispheres (Fig. 1.3). The tip is rotated placing the bevel on its side, burying the opening in the nuclear hemisphere to facilitate chopping (Fig. 1.4) and removal

Fig. 1.3 Nucleus is divided into hemispheres

of the nuclear quadrants, apex up working near the center of the capsular bag. Next, the cortex is removed with a silicone I & A tip and the posterior capsule is gently vacuumed. The capsular bag is inflated with OVD and a micro-hook is introduced through the stab incision for counter-traction during the lens implantation.

A single piece acrylic IOL (ReStor, Toric, or IQ) with a full size 6mm optic has been loaded into the C cartridge similar to the picture on the cartridge. An Osher one-handed injector (Crestpoint and B&L) is introduced into the incision bevel down and the IOL is advanced by depressing the plunger until the lens emerges. It is inserted into the capsular bag (Fig. 1.5) where it is rotated and decentered away from the incision. The incision is hydrated (Fig. 1.6) before the OVD is removed, first from within the bag behind the lens (Fig. 1.7), and then from in front of the IOL. After the lens is centered with a silicone tip, the water-tightness of the incision is confirmed (Fig. 1.8). On the first postoperative day, the cornea is almost always clear (Fig. 1.9) and the square incision appears sealed (Fig. 1.10).

Fig. 1.4 Bevel on side for chopping of quadrants

Fig. 1.5 IOL injected through 2.2 mm incision with bevel down cartridge using counter-traction technique

Fig. 1.6 Incision hydration precedes removal of OVD

Fig. 1.7 OVD evacuated from capsular bag

Fig. 1.8 Water-tightness of incision confirmed

Fig. 1.9 Clear cornea on post-op day 1

1.1.5Combining Micro-Coaxial Phacoemulsification with Torsional Ultrasound

At the 2007 annual meeting of the American Society of Cataract and Refractive Surgery, a study was presented

in which an Ophthalmology Fellow independently examined 100 consecutive routine procedures using micro-coaxial phaco with torsional ultrasound and the 12° OZil tip [37]. Ninety-eight percent of the patients attained an uncorrected visual acuity of 20/40 or better on the first postoperative day and 62% attained an