helped drive the beads in the chamber to the tip as the lens material was absorbed.

Although this cadaver eye model is a preliminary study looking at fluidics, the investigators clearly demonstrated improved fluidics and followability with torsional ultrasound compared to conventional longitudinal ultrasound.

4.3 Incision Size

As ophthalmic surgeons, we know that smaller corneal incisions induce less astigmatism and can self-seal more easily than their larger counterparts. Therefore, in theory, we would be reducing the risk of wound leakage and endophthalmitis [3].

But if the incision size is too small, the surgeon’s ability to manipulate instruments can be hindered and the potential benefits are offset. Additionally, the smallest of incisions (1.1–1.2 mm) can limit the movement of instruments and necessitate the use of unsleeved instruments, thereby increasing mechanical and thermal trauma to the wound.

To address the weaknesses of biaxial micro incisions used in bimanual phacoemulsification, some surgeons are suturing their micro incisions while others are making a third incision for IOL insertion. Both of these options offset any advantages of biaxial micro incision surgery. A more ideal system allows surgeons to perform phacoemulsification through micro incisions that will capitalize on the benefits of smaller incision sizes without increasing the downside.

Typical phacoemulsification, as previously described, operates with a longitudinal jackhammer-type motion in conventional ultrasound mode. With torsional ultrasound, the handpiece amplifies the side-to-side oscillatory motion to the phaco tip, which helps minimize the stress to the incision. As a result, the side-to-side shearing motion allows for more efficient emulsification of lens material, greatly reduces repulsion and increases followability. Laboratory and clinical studies have validated these theories.

In one ex vivo study [4], 15 human cadaver eyes were divided into three groups: group one received 2.8mm coaxial incisions, group two received 2.2mm coaxial incisions, and group three received 1.2mm biaxial incisions. All eyes underwent simulated phacoemulsification using longitudinal ultrasound with standard

settings. The investigators evaluated the architectural integrity of the different wound sizes. Spontaneous wound leakage was present in all eyes that underwent the biaxial technique, in one eye in the 2.8mm coaxial group and in none of the eyes in the 2.2mm coaxial group. Histopathologic examination of the eyes studied, revealed India Ink penetration in all of the eyes in the bimanual group and no eyes in the 2.2mm coaxial group. The biaxial incision technique also resulted in more qualitative trauma to Descemet’s membrane in the endothelium, as demonstrated by scanning electron microscopy.

In addition to improved wound integrity, Sam Masket showed that coaxial micro phacoemulsification performedthrougha2.2mmincisionresultedinsignificantly less induced astigmatism than conventional coaxial phacoemulsification through a 3.0mm incision.

In the study, all surgeries were performed through a temporally oriented, grooved, clear corneal tunnel incision, using a phaco chop technique and a 1.1 mm flared tip (Alcon Laboratories). This prospective investigation was designed as an intra-patient comparison and included 16 subjects. Astigmatism was measured preoperatively and after 6 weeks with autokeratometry in a masked fashion by a technician. The mean induced astigmatism was 0.10 diopters for the 2.2 mm incision group, which was significantly less then the 0.32 diopters of change in the 3 mm incision group [5].

While the 2.2 mm incision size is smaller than the traditional 3.0–3.2 incision size, there is essentially no learning curve for the surgeon transitioning to this unique instrumentation. Because of the coaxial nature of the procedure, this instrumentation affords stable anterior chambers intraoperatively and excellent postoperative results. A phacoemulsification surgeon can easily transition to this new technique because it is performed with almost identical surgical parameters as for standard coaxial surgery and is amiable to any approach to lens removal, be it chop, divide and conquer, or combinations thereof. 2.2–2.4 mm steel and diamond blades are readily available and enlargement of these wounds is unnecessary with the introduction of new cartridges to inject the thinner aspheric profile IOLs that are commonly used today. The incision size is readily amiable to either a standard capsulorrhexis forceps or a needle and requires no specific instrumentation.

An important advantage of the micro-coaxial technique is that, it affords the thermal protection benefit

of having a sleeve over the phaco tip. This feature is especially relevant when operating on more dense cataracts where thermal injury can be a significant concern. While results of multiple studies demonstrate that the presence of a sleeve over the phaco tip helps to protect against thermal injury, use of torsional ultrasound provides an added benefit. A study presented by Richard Mackool showed that the use of torsional ultrasound was associated with a decrease in temperature rise of about 60% compared with longitudinal ultrasound [6].

In summary. the use of 2.2–2.4 mm microincisions creates a stable, hermetically sealed environment, that reduces the likelihood of microbial contamination, thereby reducing the chance of a postoperative infection. This is in keeping with the teachings of Paul Ernest et al. [3], who proved more than a decade ago that square surface incision architecture is more resistant to deformation than other types of incisions. Additionally, incisions limited to this size are astigmatically neutral, which is a critical feature as we try to optimize our postoperative refractive results.

4.4 Torsional Ultrasound

For years, surgeons have looked for various methods to reduce the ultrasonic energy used during phacoemulsification. We have learned that ultrasonic energy correlates with corneal endothelial cell density loss, so using less energy would therefore be safer. Previously, this has been achieved using power modulation with pulse and burst ultrasound.

Torsional phacoemulsification using angled phacoemulsification needles is the latest technological advance, combining stable fluidics with a limited irrigation inflow while maintaining a secure wound construction that allows IOL insertion through a 2.2 mm incision. Oscillatory torsional amplitude creates a lateral tip movement that shears lens material and has proven cutting efficiency while at the same time reducing the amount and amplitude of the thermal energy needed (Fig. 4.3). The interesting characteristic about torsional ultrasound is what is taking place at the actual phaco tip. The oscillation at the hub, occur with the frequency of 32,000 cycles per second. With a standard Kelman style tip (approximately 20°) this translates into an actually horizontal excursion as opposed

Oscillation at Incision

Action at the Tip End - 90 microns

Fig. 4.3 Ultrasonic oscillations within the wound are translated to a side-to-side cutting action at the torsional tip. This minimizes thermal energy at the proximal portion of the phaco needle (at the incision site) while maintaining an efficient cutting action at the tip (Courtesy of Alcon Labs)

to a longitudinal excursion. The maximum horizontal excursion is 3.5 mills or 90 μm, which is almost exactly the maximum excursion with longitudinal phaco.

Compared to traditional phacoemulsification, torsional ultrasound cuts more efficiently. In torsional phaco there is a shearing effect as the tip moves to the right and to the left. In other words, 100% of the cycle is devoted to the emulsification process. In contrast, traditional ultrasonic phacoemulsification delivers less than 50% effective longitudinal energy as half the energy is lost on the back stroke. In addition, there is less heat and, hence, less thermal damage to the wound. In essence, there is less energy delivered into the eye which allows surgeons to effectively use smaller incisons, whose architecture remains unchanged throughout the procedure giving pristine incisions. This, in turn, means almost no surgically induced astigmatism and rapid healing.

Finally, angulation of the tip greatly aids in visualizing the dynamics occuring between the tip and the lens material at the distal end of the needle. The reason for this is that, unlike longitudinal phaco where movement is forward/backward, in torsional phaco the movement is from side to side, hence resulting in better visualization. This is of particular importance in difficult cases with small pupils or floppy irides.

Coaxial torsional microincision phacoemulsification through a 2.2–2.4 mm incision offers all the advantages of biaxial MICS without most of its disadvantages. Compared to biaxial MICS, fluidics are improved because adequate irrigation inflow is easily obtained and outflow is superbly controlled without surge, and without the need to lower fluidic settings or increase bottle heights to unnecessary levels. Specialized instrumentation unfamiliar to the surgeon is avoided and there is essentially no learning curve with the use coaxial MICS. Surgical techniques currently employed by the surgeon can be used with only slight modification of phacoemulsification technique. Incision size is minimized accomplishing minimal sugically induced astigmatism, maximizing protection of the corneal incision site and attaining a watertight, hermetically sealed wound to guard against endophthalmitis. Additionally current IOLs can be placed with an injector through the unenlarged 2.2 mm incision. Finally, torsional ultrasound improves cutting efficiency, minimizes the amount of energy delivered to the eye, thereby greatly reducing the chance of incisional wound burn. The synergism of torsional ultrasound when combined with the advanced fluidic system described represents a new chapter in the long history of cataract removal that is likely to endure well into the future.

1.Seibel B. Phacodynamics: Mastering the Tools and Techniques of Phacoemulsification Surgery. Slack Thorofare, NJ, 2004

2.Solomon K. Unique model illustrates fluidic flow during torsional phaco. Ophthalmology Times 2006; 31:56–58

3.Ernest PH, Fenzyl R, Lavery KT, Sensoli A. Relative stability of clear corneal incisions in a cadaver eye model. J Cataract Refract Surg 1995; 21:1:39–42

4.Berdahl JP, DeStafeno JJ, Kim T. Corneal wound architectureand integrity after phacoemulsification evaluation of coaxial, microincisional coaxial, and microincision bimanual techniques. J Cataract Refract Surg 2007; 33:510–515

5.Masket S. Coaxial 2.2mm microphaco technique reduces surgically induced astigmatism. Ophthalmology Times 2006; 31:1–2

6.Mackool RJ. Lens removal/torsional phacoemulsification: advantages of nuclear ultrasound. In: Annual ASCRS Symposium on Cararact, IOL, and Refractive Surgery, San Francisco, CA, 17–22 March 2006

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Use low-compliance tubing to decrease surge and improve overall fluidics

Use a Kelman or angled phacoemulsification needle to improve torsional efficiency Hundred percent torsional amplitude is a very efficient cutting instrument and can emulsify even the most dense nuclei

A 2.2 mm unenlarged temporal incision creates no surgically induced astigmatism

The smaller (0.9 mm) Kelman phaco needles, when used in combination with torsional ultrasound, provide more room in small pupil cases and improve the efficiency of nuclear assembly and removal