Ординатура / Офтальмология / Английские материалы / Refractive Lens Surgery_Fine, Packer, Hoffman_2005

sign” the ultrasound to match any particular technique or type of cataract (Fig. 23.6). But, with almost limitless possibilities, a few guiding principles might be helpful. Our goal is to minimize ultrasonic energy and heat, and to maximize followability and cutting efficiency. To achieve this, we must balance the pulse interval and duration. The interval, or “off” time, allows for cooling and unopposed flow to the tip. The pulse duration produces the mechanical impact, acoustical wave, fluid wave and cavitation,all of which contribute to emulsify the nucleus. Compared to squarewave pulses,rise time 2 not only produces less

total energy but its graduated off time improves followability and allows more time to develop vacuum-holding force. During sculpting, however, long intervals or “off times” may result in the needle pushing the nucleus, producing greater stress on the zonules. This becomes more likely with denser cataracts, so for a 3+ to 4+ nucleus the surgeon may want to use either linear power or rise time 1 with very short “off” intervals for sculpting, and then switch to rise time 2 for segment removal.With 1+ to 2+ cataracts, ultrasound rise time 2 would be less likely to pull through the soft eye epinucleus to dam-

age the capsule. In selecting a mode,it is helpful to remember that both pulse and fixed burst allow the surgeon to design a particular pulse cycle pattern, which is then “locked in” as the power is varied with the linear foot pedal. In contrast, multiple burst “locks in” a particular ultrasonic power and then provides linear control of the interval or “off time.”

23.10 Conclusion

The Millennium gives the surgeon the ability to access and control flow, vacuum, and ultrasound power simultaneously and to the degree that is necessary. It is the ability to deliver short bursts of phacoemulsification power and utilize vacuum as an extractive technique

– ultimately decreasing the thermal energy delivery to the eye and speeding visual recovery – that facilitates the use of sleeveless microincisional cataract surgery.

220

References

1.Fine IH, Packer M, Hoffman R (2001) Use of power modulations in phacoemulsification – choo-choo chop and flip phacoemulsification. J Cataract Refract Surg 27:188–197

2.Agarwal A, Agarwal S, Agarwal A (1999) Phakonit and laser phakonit lens removal through 0.9 mm incision. In: Agarwal A, Agarwal S, Sachdev MS et al (eds) Phacoemulsification, laser cataract surgery and foldable IOLs. Jaypee Brothers, New Delhi

3.Soscia W, Howard J, Olson R (2002) Bimanual phacoemulsification through 2 stab incisions. A wound temperature study. J Cataract Refract Surg 28:1039–1043

R.Braga-Mele · T. Devine · M. Packer

4.Tsuneoka H,Shiba T,Takahashi Y (2002) Ultrasonic phacoemulsification using a 1.4 mm incision: clinical results. J Cataract Refract Surg 28:81–86

5.Braga-Mele R, Lui E (2003) Feasibility of sleeveless bimanual phacoemulsification on the Millennium Microsurgical System. J Cataract Refract Surg 29:2199–2203

6.Braga-Mele R (2003) Bimanual sleeveless phaco on the Millennium: wound temperature and clinical studies. Paper presented at the ASCRS/ASOA Symposium; 15 Apr 2003, San Francisco, California

The last decade has given rise to some of the most profound advances in both phacoemulsification technique and technology. Techniques for cataract removal have moved from those that use mainly ultrasound energy to emulsify nuclear material for aspiration to those that use greater levels of vacuum and small quantities of energy for lens disassembly and removal. Advances in phacoemulsification technology have taken into account this ongoing change in technique by allowing for greater amounts of vacuum to be utilized. In addition, power modulations have allowed

for more efficient utilization of ultrasound energy with greater safety for the delicate intraocular environment [1, 2].

One of the most recent new machines for cataract extraction is the Staar Wave (Fig. 24.1). The Wave was designed as an instrument that combines phacoemulsification technology with new features and a new user interface. Innovations in energy delivery, high-vacuum tubing, and digitally recordable procedures with video overlays make this one of the most technologically advanced and theoretically safest machines available.

24.1Conventional Surgical Features

The Wave contains all of the customary surgical modes routinely used to perform cataract surgery, including ultrasound, irrigation/ aspiration, vitrectomy, and diathermy. The ultrasound handpiece is a lightweight (2.25 ounces), two-crystal, 40-kHz piezoelectric autotuning handpiece that utilizes a loadcompensating ultrasonic driver. The driver senses tip loading 1,000 times a second, allowing for more efficient and precise power adjustments at the tip during phacoemulsification.

One of the unique features of the Wave is its ability to adjust vacuum as a function of ultrasound power. This feature is termed “A/C” (auto-correlation) mode. It enables lens fragments to be engaged at low-vacuum levels in foot position 2. Vacuum levels are proportionally increased with increases in ultrasound power in foot position 3. Proportional increases in vacuum allow for faster aspiration of lens fragments by overcoming the repulsive forces generated by ultrasound energy at the tip. Another unique feature of the

Fig. 24.1. The Staar Wave phacoemulsification console

Wave is the random pulse mode, which randomly changes the pulse rate. This increases followability by preventing the formation of standing waves in front of the tip.

24.2New Surgical Features

Although ultrasonic phacoemulsification allows for relatively safe removal of cataractous lenses through astigmatically neutral small incisions, current technology still has its drawbacks. Ultrasonic tips create both heat and cavitational energy. Heating of the tip can create corneal incision burns [3, 4].When incisional burns develop in clear corneal incisions, there may be a loss of self-sealability, corneal edema, and severe induced astigmatism [5]. Cavitational energy results from pressure waves emanating from the tip in all directions. Although increased cavitational energy can allow for phacoemulsification of dense nuclei, it can also damage the corneal endothelium and produce irreversible corneal edema in compromised corneas with pre-existing endothelial dystrophies.Another aspect of current phacoemulsification tech-

Fig. 24.2. The tip undergoes compression and expansion, continuously changing its dimensional length. Heat is generated due to intermolecular friction

Fig. 24.3. The tip moves back and forth without changing its dimensional length. Heat due to intermolecular friction is eliminated

nology that has received extensive attention for improvement has been the attempt to maximize anterior chamber stability while concurrently yielding larger amounts of vacuum for lens removal. The Wave addresses these concerns of heat generation and chamber stability with the advent of its revolutionary “Sonic” technology and high-resistance “SuperVac” coiled tubing.

Sonic technology offers an innovative means of removing cataractous material without the generation of heat or cavitational energy by means of sonic rather than ultrasonic technology.A conventional phacoemulsification tip moves at ultrasonic frequencies of between 25 and 62 kHz. The 40-kHz tip ex-

pands and contracts 40,000 times per second, generating heat due to intermolecular frictional forces at the tip that can be conducted to the surrounding tissues (Fig. 24.2). The amount of heat is directly proportional to the operating frequency. In addition, cavitational effects from the high-frequency ultrasonic waves generate even more heat.

Sonic technology operates at a frequency much lower than ultrasonic frequencies. Its operating frequency is in the sonic rather than the ultrasonic range, between 40 and 400 Hz. This frequency is 1–0.1% lower than ultrasound, resulting in frictional forces and related temperatures that are proportionally reduced. In contrast to ultrasonic tip motion,

Fig. 24.4. Phacoemulsification tip in sonic mode being grasped with an ungloved hand, demonstrating lack of heat generation

Fig. 24.5. High-magnification view of SuperVac coiled tubing

Fig. 24.6. When braking occlusions, regular phacoemulsification systems generate a flow surge in linear relation with the vacuum. The SuperVac tubing dynamically limits the flow surge. As shown, the surge at 500 mmHg or higher is the same as for a regular phacoemulsification system operating at 200 mmHg

Chapter 24

the sonic tip moves back and forth without changing its dimensional length (Fig. 24.3). The tip of an ultrasonic handpiece can easily exceed 500° Celsius in a few seconds, while the tip of the Wave handpiece in sonic mode barely generates any frictional heat, as intermolecular friction is eliminated (Fig. 24.4). In addition, the sonic tip does not generate cavitational effects and thus true fragmentation, rather than emulsification or vaporization, of the lens material takes place. This adds more precision and predictability in grooving or chopping and less likelihood for corneal endothelial compromise or incisional burns.

The most amazing aspect of the sonic technology is that the same handpiece and tip can be utilized for both sonic and ultrasonic modes. The surgeon can easily alternate between the two modes using a toggle switch on the foot pedal when more or less energy is required. The modes can also be used simultaneously with varying percentages of both sonic and ultrasonic energy. We have found that we can use the same chopping cataract extraction technique [4] in sonic mode as we do in ultrasonic mode, with no discernible difference in efficiency.

The ideal phacoemulsification machine should offer the highest levels of vacuum possible with total anterior chamber stability. The Staar Wave moves one step closer to this ideal with the advent of the SuperVac tubing (Fig. 24.5). SuperVac tubing increases vacuum capability to up to 650 mmHg while significantly increasing chamber stability. The key to chamber maintenance is to achieve a positive fluid balance, which is the difference between infusion flow and aspiration flow. When occlusion is broken, vacuum previously built in the aspiration line generates a high aspiration flow that can be higher than the infusion flow. This results in anterior chamber instability. The coiled SuperVac tubing limits surge flow resulting from occlusion breakage in a dynamic way. The continuous change in direction of flow through the coiled tubing increases resistance through the tubing at

clusion of the tip (Fig. 24.6). This effect only takes place at high flow rates (greater than 50 cc/min). The fluid resistance of the SuperVac tubing increases as a function of flow and unoccluded flow is not restricted.

Staar has also recently released its cruisecontrol device, which has a similar end result of increasing vacuum capability while maintaining anterior chamber stability. The cruise control (Fig. 24.7) is inserted between the phacoemulsification handpiece and the aspiration line. It has a small port at the end attached to the aspiration line to restrict flow when high flow rates are threatened, such as during occlusion breakage. A cylindrical mesh within the cruise-control tubing is designed to capture all lens material before it reaches the restricted port, thus occlusion of the port is prevented. The mesh is designed with enough surface area to guarantee that aspiration fluid will always pass through the device. This device is especially important during bimanual phacoemulsification, as the anterior chambers of eyes undergoing this technique are susceptible to chamber instability if postocclusion surge develops.

24.3New User Interface

Perhaps the most advanced feature on the Wave is its new user interface. The Wave Powertouch computer interface mounts onto the Staar cart above the phacoemulsification console. The touchscreen technology allows the user to control the surgical settings by touching parameter controls on the screen. The interface utilizes Windows software and is capable of capturing digitally compressed video displaying the image live on the monitor screen. A 6-gigabyte hard disk can store up to 8 hours of video without the need for VHS tapes.

The most useful and educational aspect of the Wave interface is the event list, which displays multiple data graphs to the right of the

Fig. 24.8. Wave video overlay demonstrating multiple data graphs to the right with power, vacuum, flow, and theoretical tip temperature parameters

surgical video (Fig. 24.8). The event list displays recorded power, vacuum, flow, theoretical tip temperature, and risk factor for incisional burns on a constantly updated timeline. The vertical line in each graph represents the actual time event occurring on the video image. Surgical events to the left of the line represent past events, while data to the right of the line represent future events ready to occur. A CD-Rom recorder can be used to transfer surgical video and data graphs from the hard drive to a writable CD. This allows the surgeon to view each case on any Windows home or office computer or use the images for presentations. The ability to review surgical parameters on a timeline as the video image is being displayed allows surgeons to analyze unexpected surgical events as they are about to occur in a recorded surgical case. This information can then be used to adjust parameters or surgical technique to avoid these pitfalls in future cases. Staar eventually plans to transmit live surgical cases over the internet so that surgeons anywhere in the world can log on and watch a selected surgeon demonstrate his or her technique with real-time surgical parameter display.

24.4Conclusion

The Staar Wave is one the most advanced phacoemulsification systems available today. The use of sonic rather than ultrasonic energy for the extraction of cataracts represents a major advancement for increasing the safety of cataract surgery. Sonic mode can be used by itself or in combination with ultrasonic energy, allowing for the removal of all lens densities with the least amount of energy delivered into the eye. SuperVac tubing allows higher levels of vacuum to be used for extraction with increased chamber stability by nature of the resistance of this tubing to high flow rates when occlusion is broken. Finally, the addition of advanced video and computer technology for recording and reviewing surgical images and parameters will allow surgeons further to improve their techniques and the techniques of their colleagues through better communication and teaching.

References

1.Fine IH (1998) The choo-choo chop and flip phacoemulsification technique. Operative Techn Cataract Refract Surg 1:61–65

2.Fine IH, Packer M, Hoffman RS (2001) The use of power modulations in phacoemulsification of cataracts: the choo-choo chop and flip phacoemulsification technique. J Cataract Refract Surg 21:188–197

3.Fine IH (1997) Special report to ASCRS members: phacoemulsification incision burns. Letter to American Society of Cataract and Refractive Surgery members

4.Majid MA, Sharma MK, Harding SP (1998) Corneoscleral burn during phacoemulsification surgery. J Cataract Refract Surg 24:1413– 1415.

5.Sugar A, Schertzer RM (1999) Clinical course of phacoemulsification wound burns. J Cataract Refract Surg 25:688–692

One of the more advanced and versatile phacoemulsification machines on the market today is the AMO Sovereign (Advanced Medical Optics, Santa Ana, CA). The Sovereign offers all of the traditional features of phacoemulsification machines and has been recently upgraded with the addition of WhiteStar technology. WhiteStar is a new technology in that an ultrapulse mode is able to modulate the delivery of energy by changing both the duration and the frequency of ultrasonic vibrations. Energy is delivered in extremely brief, microsecond bursts,interrupted by rest intervals. The burst length and rest period can be varied independently of each other, yielding numerous modes of varying duty cycles to choose from (Fig. 25.1).

The addition of WhiteStar technology to the Sovereign machine reduces thermal escalation at the wound while maintaining the cutting efficiency seen with continuousmode ultrasound and improving nuclear fragment followability [1]. Reduced thermal energy results from the ultrashort delivery of energy and the interval rest period.Despite the short bursts of energy,each pulse of WhiteStar ultrasound has been demonstrated to deliver similar cutting ability as that delivered with continuous-mode ultrasound. This has been demonstrated by Dr Mark E. Schafer, wherein the acoustical energy of WhiteStar pulses was transposed into electrical signals using a transducer. Similarly, the acoustical signal of continuous-mode phacoemulsification was