The last decade has given rise to some of the most profound advances in both phacoemul- sification technique and technology. Tech- niques 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 disassem- bly and removal. Advances in phacoemulsifi- cation 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 in- traocular 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 in- strument 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.
Richard S. Hoffman, I. Howard Fine, Mark Packer
CORE MESSAGES
2 Sonic technology offers an innovative means of removing catarac- tous material without the generation of heat or cavitational energy by means of sonic rather than ultrasonic technology.
2 Both the Staar SuperVac coiled tubing and the cruise control limit surge flow that occurs during high flow rates, such as those that develop upon loss of occlusion.
2 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.
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24.1 Conventional Surgical Features
The Wave contains all of the customary surgi- cal 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 load- compensating ultrasonic driver. The driver senses tip loading 1,000 times a second, al- lowing for more efficient and precise power adjustments at the tip during phacoemulsifi- cation.
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 ul- trasound power in foot position 3. Propor- tional increases in vacuum allow for faster as- piration of lens fragments by overcoming the repulsive forces generated by ultrasound en- ergy at the tip. Another unique feature of the
Wave is the random pulse mode, which ran- domly changes the pulse rate. This increases followability by preventing the formation of standing waves in front of the tip.
24.2 New Surgical Features
Although ultrasonic phacoemulsification al- lows 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 inci- sions, there may be a loss of self-sealability, corneal edema, and severe induced astigma- tism [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. 24.1. The Staar Wave phacoemulsifi- cation console
nology that has received extensive attention for improvement has been the attempt to maximize anterior chamber stability while concurrently yielding larger amounts of vac- uum for lens removal. The Wave addresses these concerns of heat generation and cham- ber stability with the advent of its revolution- ary “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 ultra- sonic technology.A conventional phacoemul- sification 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 fric- tional 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. 24.2. The tip undergoes compression and expansion, continuously changing its dimen- sional length. Heat is generated due to inter- molecular friction
Fig. 24.3. The tip moves back and forth with- out changing its dimensional length. Heat due to intermolecular friction is eliminated
Fig. 24.4. Phacoemulsification tip in sonic mode being grasped with an ungloved hand, demon- strating lack of heat generation
Fig. 24.5. High-magnification view of SuperVac coiled tubing
Fig. 24.6. When braking occlusions, regular phacoemul- sification systems generate a flow surge in linear relation with the vacuum. The Super- Vac 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
Fig. 24.7. Schematic representation of the Staar cruise control
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 inter- molecular friction is eliminated (Fig. 24.4). In addition, the sonic tip does not generate cav- itational 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 en- dothelial 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 be- tween the two modes using a toggle switch on the foot pedal when more or less energy is re- quired. The modes can also be used simulta- neously 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 pos- sible 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 vacu- um capability to up to 650 mmHg while sig- nificantly 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 previous- ly built in the aspiration line generates a high aspiration flow that can be higher than the in- fusion 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
high flow rates, such as upon clearance of oc- 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 Super- Vac tubing increases as a function of flow and unoccluded flow is not restricted.
Staar has also recently released its cruise- control device, which has a similar end result of increasing vacuum capability while main- taining anterior chamber stability. The cruise control (Fig. 24.7) is inserted between the phacoemulsification handpiece and the aspi- ration line. It has a small port at the end at- tached 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 de- signed 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 insta- bility if postocclusion surge develops.
24.3 New User Interface
Perhaps the most advanced feature on the Wave is its new user interface. The Wave Pow- ertouch 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 moni- tor 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 dis- plays multiple data graphs to the right of the
surgical video (Fig. 24.8). The event list dis- plays recorded power, vacuum, flow, theoreti- cal tip temperature, and risk factor for incisional burns on a constantly updated timeline. The vertical line in each graph rep- resents 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 Win- dows home or office computer or use the im- ages for presentations. The ability to review surgical parameters on a timeline as the video image is being displayed allows sur- geons to analyze unexpected surgical events as they are about to occur in a recorded sur- gical case. This information can then be used to adjust parameters or surgical technique to avoid these pitfalls in future cases. Staar even- tually 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.
24.4 Conclusion
The Staar Wave is one the most advanced phacoemulsification systems available today.
The use of sonic rather than ultrasonic ener- gy 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 de- livered into the eye. SuperVac tubing allows higher levels of vacuum to be used for extrac- tion 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 re- viewing surgical images and parameters will allow surgeons further to improve their techniques and the techniques of their col- leagues 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 pha- coemulsification technique. J Cataract Refract Surg 21:188–197
3. Fine IH (1997) Special report to ASCRS mem- bers: phacoemulsification incision burns. Let- ter to American Society of Cataract and Re- fractive Surgery members
4. Majid MA, Sharma MK, Harding SP (1998) Corneoscleral burn during phacoemulsifica- tion surgery. J Cataract Refract Surg 24:1413–
1415.
5. Sugar A, Schertzer RM (1999) Clinical course of phacoemulsification wound burns. J Cata- ract Refract Surg 25:688–692
Fig. 24.8. Wave video overlay demonstrating mul- tiple data graphs to the right with power, vacuum, flow, and theoretical tip temperature parameters
