chamber. The procedure has no significant learning curve and therefore is no more difficult than when performed through a 2.8-mm incision.

Both the companies also manufacture a one-piece acrylic IOL and injector, which is capable of implanting the IOL through the 2.2 mm unenlarged incision.

B&L now has a new Akrios hydrophilic acrylic IOL that can be implanted through a 1.8-mm incision.

Sub 2 mm incision phaco is a reality, but not an accepted alternative, at present. When IOLs are available to be introduced through these micro-incisions, the surgical community will embrace the procedure.

3.7.3.1 Irrigation and Aspiration

Similar to phaco, the anterior chamber stability during irrigation and aspiration (I/A) is due to an equilibrium of inflow and outflow. Wound outflow can be minimized by employing a soft sleeve around the I/A tip. Combined with a small incision (2.8–3 mm), a deep and stable anterior chamber will result. Generally, a 0.3-mm I/A tip is used. With this orifice, a vacuum of 500 mmHg and a flow of 20 mL/min is excellent to tease out the cortex from the capsular fornices.

Linear vacuum allows the cortex to be grasped under the anterior capsule with low vacuum and be drawn into the center of the pupil at the iris plane. There, in the safety of a deep anterior chamber, vacuum can be increased and the cortex aspirated.

Bimanual I&A is also a viable procedure. A 21-gauge irrigating cannula provides inflow through one paracentesis while an unsleeved 21-gauge aspiration cannula is used through the opposite paracentesis. The instruments can be easily switched making the removal of the stubborn cortex considerably easier.

to this requirement. It is through this crucial attitude of relentless evaluation of the interaction of the machine and the phaco procedure, that a skillful surgeon will find innovative methods to enhance the technique.

Take Home Pearls

ßThe capability of the current phaco machines to take advantage of hyper-pulse phaco and nonlongitudinal phaco energy, and the enhanced fluid management of pumps and software, has revolutionized the way, phacoemulsification is performed.

ßIn the past, phaco demanded the occlusion of the tip with inevitable post-occlusion surge.

ßPresently the method is partial occlusion, and hence related to this change, the fluid equilibrium in the anterior chamber is significantly different than in the past. With partial occlusion phaco the anterior chamber is notably more stable with negligible surge.

ßSoftware management of energy application and fluidics has superbly augmented the surgeons’ command of the stability of the anterior chamber.

ßThere is, therefore, less risk of torn posterior capsules during surgery and less risk of vitrectomy. This leads to improved outcomes as determined by the rapidity of the return of vision, as well as decreased corneal edema and endothelial cell loss.

ßCreative technology in phaco machine design is an enormous enhancement over previous technologies.

3.8 Conclusion

The phaco process is a balance of technology and technique. Awareness of the principles that influence phaco machine settings is a prerequisite for the performance of a proficient and safe operation. Additionally, often during the procedure, there is a demand for modification of the initial parameters. A thorough understanding of the fundamental principles will enhance the capability of the surgeon for an appropriate response

Reference

1.Packer M, Fishkind W, Fine IH, Seibel B, Hoffman R (2005) The physics of phaco: a review. J Cataract Refract Surg 31:424–431

2.Donnenfeld ED, Olson RJ, Solomon R, Finger PT, Biser SA, Perry HD, Doshi S (2003) Efficacy and wound-temperature gradient of WhiteStar phacoemulsification through a 1.2 mm incision. J Cataract Refract Surg 29(6):1097–1100

3. Soscia W, Howard JG, Olson RJ (2002) Microphacoemulsification with WhiteStar: a wound-temperature study.

JCataract Refract Surg 28(6):1044–1046

4.Fine IH, Packer M, Hoffman RS Power modulations in new phacoemulsification technology: improved outcomes (2004)

JCataract Refract Surg 30(5):1014–1019

Further Reading

1.Buratto L, Osher RH, Masket S, eds. Cataract Surgery in Complicated Cases. Thorofare, NJ: SLACK Incorporated; 2001.

2.Fishkind WJ, ed. Complications in Phacoemulsification: Recognition, Avoidance, and Management. New York: Thieme Publishers; 2001.

3.Fishkind WJ. Pop Goes the Microbubbles. ESCRS Film Festival Grand Prize Winner, 1998.

4.Fishkind WJ, Neuhann TF, Steinert RF. The Phaco Machine in Cataract Surgery Technique: Complications & Management. 2nd Ed. Philadelphia: W.B. Saunders and Co; 2004.

5.Seibel BS. Phacodynamics: Mastering the Tools and Techniques of Phacoemulsification Surgery. 4th edition Thorofare, NJ: SLACK Incorporated; 2005.

6.“From phaco-cutting to true phacoemulsification.” Miyoshi, T. Video competition grand prize winner ASCRS, ESCRS 2007.

ßTorsional phacoemulsification is a more efficient use of ultrasound than longitudinal phacoemul-

sification

ßFollowability of nuclear material is improved with torsional ultrasound

ßTorsional phacoemulsification combined with less compliant tubing allows surgeons to use

more conservative fluidic settings, lessening the potential for complications

ßTorsional phacoemulsification allows for microincisonal surgery (2.3–2.4mm) through which

currently available IOLs can be placed

ßMicroincisions of 2.2 mm produce negligible surgically induced astigmatism

4.1 Introduction

Charles Kelman’s revelation in the dentist chair, leading to the invention of ultrasonic phacoemulsification in 1967, began the relentless march toward eversmaller incision sizes to be utilized in cataract surgery. The original procedure by Dr. Kelman used a fourpound ultrasound hand piece in a surgical procedure that took 4 h (including 41 min of ultrasound time) and resulted in endophthalmitis and eventual phthisis. It is a testament to the perseverance and ingenuity of many phacoemulsification pioneers that the procedure has evolved to its current state where a cataract can be removed in minutes, and it is one of the safest and most successful surgical methods ever developed.

Each development in phacoemulsification surgery has set the stage for the next. Kaizen, a Japanese word meaning gradual, orderly, continuous improvement, exemplifies the persistent ongoing development of both

S. S. Lane

University of Minnesota, 2950 Curve Crest Boulevard, Stillwater, MN 55082, USA;

e-mail: sslane@associatedeyecare.com

phacoemulsification technology and techniques. In the early days of phacoemulsification, the smaller incision size drove intraocular lens (IOL) technology to develop foldable lenses that would fit through these smaller incisions (usually about 3mm). As IOL technology evolved, lenses and injector systems were introduced that allowed lens implantation to be performed through smaller incisions, driving phacoemulsification instrumentation technology to allow cataract removal through even smaller incisions. With these current advances, we have come full circle. The advent of a new generation of IOLs and injectors, in combination with increasing patient expectations for excellent uncorrected acuity, the desire to better control the unpredictability of surgically induced astigmatism and the minimization of incision size to prevent incision wound incompetence, allows us now to perform phacoemulsification through incisions that are smaller than most modern IOLs can go through. The challenge, once again, has been to find an IOL that can be placed thru an ultra-small opening (sub-2.0mm), but importantly not to compromise on the attributes of current IOLs or on the phacoemulsification procedure itself, which is so successfully performed worldwide.

Biaxial microincisional cataract surgery (MICS) performed through two sub-2 mm incisions, using the

irrigation instrument through one site and an unsleeved phaco tip through the other, became possible several years ago when advances in phacoemulsification power modulation technology helped solve most of the problems associated with heat generation at the incision. While biaxial MICS has many proponents who expound upon its multiple advantages, the procedure has not been widely embraced as other surgeons perceive various drawbacks. These include: a difference in fluidics, a new learning curve, wound damage/distortion, and the logic of performing cataract surgery through a sub-2 mm incision without the availability of a microincision IOL, which would be able to provide high-quality and stable vision with a low risk of posterior capsule opacification (PCO).

Microcoaxial phacoemulsification (2.2mm incision or smaller) presents the unique characteristics of preserving many of the advantages of coaxial small incision surgery and biaxial MICS, while offering significant advantages over both.

4.2The Fluidics of Coaxial Microincisional Phacoemulsification

Traditional longitudinal ultrasound requires surgeons to use relatively high aspiration flow and vacuum settings to overcome the repulsive effect of the phaco tip’s forward strokes. With coaxial microincisional phaco, fluidic settings need to be decreased to compensate for the reduced irrigation inflow. This decrease in irrigation flow has to be compensated by a similar decrease of aspiration flow and vacuum limit or by raising irrigation bottle height. Therefore, with coaxial microsurgery, there is roughly a 30% decrease of irrigation flow if surgeons switch from a 2.6–2.8 mm incision to a 2.2–2.4 mm incision if the bottle height is not adjusted. If longitudinal ultrasound is utilized with lower settings, efficiency and safety of the procedure might be compromised. High bottle heights can lead to increased fluidic turbulence that can prove problematic during the procedure and jeopardize optimal postoperative results.

A significant decrease of aspiration flow results in a significant decrease of the process of nuclear pieces being attracted to the phacoemulsification tip since the speed of the fluid stream (aspiration flow) determines how fast the nuclear fragment is transported to the phaco

Fig. 4.1 Intraoperative photograph of longitudianl phacoemulsification illustrating repulsion of a nuclear fragment seen just above the phaco tip

tip opening [1]. This is particularly important when one realizes that traditional longitudinal ultrasound does not only emulsify the nuclear material by the forward stroke of the phaco tip, but also repels the nucleus at the same time. This paradox is, in fact, the greatest drawback of longitudinal ultrasound. Longitudinal ultrasound depends on high attractive forces-high aspiration flow and high vacuum to compensate for its intrinsic repulsive forces (Fig. 4.1).

Operating under conditions of high vacuum settings has the potential of increasing the possibility of surgical complications. When occlusion of the phaco tip is broken with a high vacuum by the emulsification of lens material on or in the phaco tip, the immediate return of the peristaltic pump tubing to its original dimension after being contracted by a high vacuum results in a sudden outflow of fluid from the fluid paths and, potentially, the anterior chamber. This could lead to a sudden shallowing of the anterior chamber, contact of the phaco needle with the capsule or other anterior segment structures, and potentially rupture the posterior capsule. This phenomenon is called surge and its severity is determined by the height of the vacuum and the compliance of the tubing. The more compliant (softer, more pliable) the tubing, the more contraction occurs and the worse the surge flow is. The new Intrepid FMS system (Alcon, Fort Worth, TX) increases the rigidity of the aspiration tubing, which reduces the occlusion break surge response significantly. This reduction in tubing contracture improves anterior chamber stability, decreasing the need to adjust flow and vacuum settings or raising bottle heights to very high levels.

Fig. 4.2 Intraopertive photograph of microincision torsional phacoemulsification illustrating attraction of a nuclear fragment to the tip during the emulsification process

The introduction of torsional ultrasound with its side- to-side ultrasonic sheering motion of the phaco tip has led to a paradigm shift in fluidics management during micro-coaxial surgery. High vacuum is no longer necessary to obtain efficient and effective emulsification as there is no repulsion that the system needs to overcome (Fig. 4.2). This allows surgeons a broader range in vacuum limits and bottle heights than is offered with modulated, longitudinal ultrasound.

Another advantage to lower fluidic settings is that, dispersive viscoelastic is not aspirated and may further protect the delicate intraocular structures during complicated cases. Compared to biaxial MICS, a microcoaxial approach avoids problems with intraoperative fluid leakage and does not require special instrumentation or modifications to the surgical technique that create a learning curve for biaxial MICS. In surgical challenges such as weak zonules, a posterior capsular rupture, or floppy iris syndrome, torsional ultrasound allows us to adjust the fluidics parameters to maintain low pressure fluctuations and reduced turbulence.

Dr. Kerry Solomon [2] developed a model to help determine how the phacoemulsification tip mechanics and intraocular fluidics flow contribute to the improved attractability and followability of nuclear material when using torsional phacoemulsification. The method he developed was based on analysis of the intraoperative dynamics of microcarrier beads suspended in the balanced salt solution (BSS) irrigating fluid. The beads were constructed of a cross-linked polystyrene material that have a collagen surface coating and are very small. They range in diameter from 125 to 212μm and

have a surface area of 390 cm2/g, and a specific gravity of 1.02, which allows them to remain suspended in BSS. In their study, 30 fresh porcine eyes and 16 fresh human globes from bilateral donors (that were not suitable for transplantation) were utilized.

They took the same amount of beads by weight (50 mg) and the same amount of BSS (1.5 mL) and injected them into each eye via the irrigation tubing. The same person performed injections at a steady rate in a standardized way for each eye. After this, phacoemulsification was carried out on each eye using a standardized procedure. A 2.6 mm incision, a vacuum rate with a limit of 350 mg Hg, a bottle height of 90 cm, and the same aspiration flow rate (AFR) of 35 mL/min was used for each case. Ultrasound power was varied so that they could study fluidics through the entire range of power modulation: 100, 50, and 25% to evaluate clearance time of the collagen beads through the anterior chamber. High speed photography was used to evaluate the difference in fluid patterns by computer tracing of ten random beads within the solution. The flow pattern was tracked within the anterior chamber between torsional and pulse traditional ultrasound. Each evaluation was videotaped in real time from the surgeon’s view and from a side view and also with a high-speed camera that captures 300 frames/s. The high-speed camera was used to demonstrate different fluidic patterns of bead flow in the periphery and at the central needle tip with and without lens material.

The investigators looked at how long the beads took to clear the system, first using ultrasonic phaco and then using torsional phaco at 25% power, 50% power, and then 100% power. They found that there was a 50% quicker removal of the beads with the torsional vs. conventional ultrasound across the entire range of power modulations.

The high-speed camera footage and bead tracking showed that, with traditional longitudinal phaco, beads were attracted to the tip and then repelled by the pulsing of traditional ultrasound. The beads would then continue to be repelled and travel away from the tip before finally being attracted and cleared from the anterior chamber.

Evaluation of high-speed footage of the torsional fluidics showed little to no repulsion of the beads. Once the beads got in the path of the phaco tip, the beads that were tracked were aspirated into the tip. Analyzing the movement of the beads with nuclear material demonstrated that, once occlusion was broken, the fluidics