Ординатура / Офтальмология / Английские материалы / Modern Cataract Surgery_Kohnen_2002

Fig. 1. The Staar Wave phacoemulsification console.

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 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.

New 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 selfsealability, 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 technology that has received extensive attention for improvement has been the attempt to maximize

Rest

Compression

Expansion

Fig. 2. Regular ultrasonic tip motion: the tip undergoes compression and expansion continuously changing its dimensional length. Heat is generated due to intermolecular friction.

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 phaco tip moves at ultrasonic frequencies of between 25 and 62 kHz. The 40-kHz tip expands 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. 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, the sonic tip moves back and forth without changing its dimensional length (fig. 3). The tip of an ultrasonic handpiece can easily exceed 500°C in a few seconds while the tip of the Wave handpiece in Sonic mode barely generates any frictional heat since intermolecular friction is eliminated (fig. 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.

Rest

Forward

Backwards

Fig. 3. Sonic tip motion: the tip moves back and forth without changing its dimensional length. Heat due to intermolecular friction is eliminated.

Fig. 4. Phacoemulsification tip in Sonic mode being grasped with an ungloved hand demonstrating lack of heat generation.

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

Fig. 5. Phacoemulsification handpiece attached to SuperVac coiled tubing.

Fig. 6. High magnification view of SuperVac coiled tubing.

with varying percentages of both sonic and ultrasonic energy. We have found that we can use our same chopping cataract extraction technique [4] in sonic mode as we utilized in ultrasonic mode with no discernable 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 their SuperVac tubing (fig. 5, 6). SuperVac tubing increases vacuum capability up to 650 mm Hg while significantly increasing chamber stability. The key to chamber maintainance 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 high flow rates such as upon clearance of occlusion of the tip (fig. 7, 8). This effect only takes place at high flow rates ( 50 cm3/min). The fluid resistance of the SuperVac tubing increases as a function of flow and unoccluded flow is not restricted.

New 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

Fig. 9. The Wave Powertouch™ computer interface mounts onto the Staar cart above the phacoemulsification console.

the phacoemulsification console (fig. 9). 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-GB hard disk can store up to 8 h of video without the need for VHS tapes.

The most useful and educational aspect of the Wave interface is the Event List that displays multiple data graphs to the right of the surgical video (fig. 10). 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

Fig. 10. Wave video overlay demonstrating multiple data graphs to the right with power, vacuum, flow, and theoretical tip temperature parameters. Note the vacuum is 500 mm Hg and the aspiration flow rate is 40 cm3/min.

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 can allow surgeons the capability of analyzing 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.

Conclusion

The Staar Wave is one of 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 for the use of 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 to further improve their techniques and the techniques of their colleagues through better communication and teaching.

References

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

2Fine IH, Packer M, Hoffman RS: The use of power modulations in phacoemulsification of cataracts: The choo-choo chop and flip phacoemulsification technique. J Cataract Refract Surg 2001;27:188–197.

3Fine IH: Special Report to ASCRS Members: Phacoemulsification Incision Burns. Letter to American Society of Cataract and Refractive Surgery Members, 1997.

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

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

Dr. I. Howard Fine, 1550 Oak Street, Suite 5, Eugene, OR 97401 (USA) Tel. 1 541 687 2110, Fax 1 541 484 3883, E-Mail hfine@finemd.com