Introduction

New technology brings challenges and opportunities to the anterior segment surgeon. The drive toward less traumatic surgery and more rapid visual rehabilitation after cataract surgery has spawned various modalities for reducing incision size and decreasing energy utilization.

Elimination of the frictional heat produced during ultrasound phacoemulsification represents an important step toward further reduction of incision size. Laser technology, including the Er:YAG and Nd:YAG lasers, offers one approach to the elimination of thermal energy during phaco. The sonic phacoemulsification system (e.g., Staar Surgical, Monrovia, Calif.) offers another approach to eliminating heat and danger of thermal injury to the cornea. Modification of ultrasound energy through power modulation, such as in the WhiteStar (Allergan, Irvine, Calif.) and NeoSonix (Alcon, Ft. Worth, Texas) systems, offers yet another route leading to elimination of heat and reduction of incision size. Other new modalities under investigation include vortex phacoemulsification (Catarex, Bausch & Lomb, Claremont, Calif.) and a fluid-based cataract extraction system, (Aqualase, Alcon).

Er:YAG Laser Phacoemulsification

Er:YAG laser phacoemulsification represents an emerging technology in cataract surgery. Several potential advantages of the erbium laser over ultrasound as a modality for cataract extraction have been observed, including relative reduction in the energy requirement for cataract extraction and the absence of any potential for thermal injury to the cornea.

Premier Laser Systems (Irvine, California) developed the Centauri Er:YAG laser and received U.S. Food and Drug Administration (FDA) approval for anterior capsulotomy in 1991. However, the company, which was also involved in the development and marketing of other laser devices and applications, filed chapter 11 bankruptcy in 2000.¹ In 1997, Asclepion-Meditec (Jena, Germany) introduced a new erbium laser system for ophthalmic microsurgery, the MCL-29. The principal initial applications of the laser included construction of the sclerostomy for glaucoma surgery,² ab interno trabecular ablation, and goniotomy.^3,4 However, by 1998, the MCL-29 had received approval in Europe for cataract extraction based on clinical studies in Spain, Italy, and Germany.⁵

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Slide 2

The Er:YAG laser was initially investigated for cataract surgery by Peyman and Katoh⁶ and Tsubota⁷ in the 1980s. The laser produces a wavelength of 2.94 µm, which lies in the infrared spectrum and is highly absorbed by water (Slide 1). Walsh and Cummings⁸ calculated the ablation depth at 1 µm. However, Lin and colleagues,⁹ demonstrated that absorption of laser energy in the first micron produces a cavitation bubble and, therefore, allows penetration beyond 1 µm. Extension of penetration occurs because a second laser pulse traverses the first cavitation bubble to form a second bubble. Additionally, variation in bubble size may occur with variation in power and fiber size.¹⁰ According to Höh, at energy settings of 10 microjoules (mJ) of single pulse energy and 200 microseconds (µs) of single pulse duration, the extent of the first bubble is approximately 1 mm in water.¹¹ In water, the cavitation bubble collapses instantaneously. However, in the nuclear material of the lens, the collapse of the bubble occurs more slowly. The laser beam can travel across the first bubble and form a second bubble in line with the first. If a third bubble forms it increases the effective range of the laser to 3 mm (Slide 2). Direct concussive effects of the laser energy propagation wave disrupt the lens material, creating an emulsate that is aspirated from the eye.

Slide 3

The optical fiber of the MCL-29 consists of zirconium fluoride. Other materials that have been investigated for the delivery of Er:YAG energy include sapphire, silica, and germanium oxide. Sapphire transmits energy well but is quite brittle. Silica has poor transmission and is quite rigid. Both zirconium fluoride and germanium oxide have toxic properties upon degradation in an aqueous environment and, therefore, must be connected to a nontoxic tip.¹⁰ In the MCL-29 system, the fiber is coupled to a handpiece configured with infusion and aspiration facilities.

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One of the principal advantages of laser cataract extraction in general and of the Er:YAG system in particular is the absence of thermal energy. In ultrasonic phacoemulsification, electrical energy is converted by piezo electric crystals into mechanical energy, which emulsifies the lens material by means of tip vibration. This vibration produces friction and, therefore, liberates heat (Slide 3). For this reason, ultrasonic phacoemulsification needles require an irrigation sleeve for cooling. This irrigation sleeve carries heat away from the tip but necessitates an incision size larger than the tip alone. Nevertheless, ultrasonic phacoemulsification still carries with it the potential for thermal injury to the cornea in case of diminished flow. Flow and aspiration problems may be caused by compression of the irrigation sleeve at the incision site, kinking of the sleeve during manipulation of the handpiece, tip clogging by nuclear or viscoelastic material, and inadequate flow rate or vacuum settings.¹² Because the tip of the erbium laser system does not produce relevant heating effects (Slide 4), the risk of corneal burn is eliminated and the potential for reduced incision size is created.¹³

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Höh and Fischer¹⁴ reported the results of a pilot study of the MCL-29 in June 2000. The handpiece they used had the familiar design of an ultrasonic handpiece, with an irrigation sleeve. Their surgical technique involved a divide and conquer method performed through a 3.2-mm incision (Slide 5, Slide 6, Slide 7, Slide 8, and Slide 9). The level of nuclear hardness of most of the cataracts was 1 on a scale of 0 to 4.

Slide 8

The investigators completed removal of the cataract with the erbium laser in 36 of 40 eyes, but were required to convert to another method in the remaining eyes due to prolonged surgical time (three cases) or capsule rupture with vitreous prolapse (one case).

Slide 9

The median total energy applied to complete cataract extraction in this pilot study was 38.5 Joules (J). This value compares favorably with the values published for divide and conquer ultrasonic phacoemulsification, 3264 ± 1218 J.¹⁵ However, it remains somewhat higher than the single digit average Joules reported by Fine, Packer, and Hoffman for the choo-choo chop and flip phacoemulsification technique with power modulations.¹⁶

The median time of phacoemulsification in the pilot study measured 3 minutes. Höh and Fischer describe a learning curve, with increasing experience leading to a decrease in phaco time. The also found a significant correlation between grade of nucleus and number of pulses, and total energy and phaco time.

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Slide 11

The authors demonstrated a median 0.96% decline in the endothelial cell count after 2 months. This decline compares favorably with reported values of endothelial cell decline following ultrasonic phacoemulsification, which range as high as 18%.¹⁷ Dick and associates¹⁸ showed 4.2 % endothelial cell loss for nuclear densities of 2+ or less, which are similar to most of those in the pilot study. The authors point out that this favorable comparison can be drawn despite longer phaco times and increased volumes of irrigation fluid through the eye. They suggest, therefore, that laser phacoemulsification may be gentler to the corneal endothelium than ultrasound. However, they state this effect may be related to energy level.

Slide 12

Positive results with the MCL-29 led to the development of the Phacolase (Asclepion-Meditec) (Slide 10 and Slide 11). This Er:YAG laser features a variable pulse energy from 5 mJ to 50 mJ, as well as a variable frequency from 10 Hz to 100 Hz. In its present form, the Phacolase system is coupled to a Megatron irrigation/aspiration (I&A) pump (Geuder, Heidelberg). The Megatron has a peristaltic pump with venturi-like effect. The Phacolase handpiece incorporates the laser fiber inside the aspiration port (Slide 12 and Slide 13). A bidirectional foot switch is used which separates infusion and aspiration from laser energy (Slide 14 and Slide 15). Moving the foot pedal laterally increases the repetition rate in a linear fashion. Pushing the pedal down provides linear control of vacuum.

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The evolution of technology has been accompanied by advances in technique. Höh developed a chop technique that he reported in 1999.¹¹ In his technique, the bottle height is set at 85 cm, the flow rate at 25 mL/min and the vacuum at 400 mm Hg. The laser energy is set at 10 mJ per pulse for all except very hard nuclei. Following hydrodissection and hydrodelineation, a small bowl or divot is sculpted in the proximal anterior nucleus with the laser tip (Höh H, personal communication). This divot is necessary to provide a point of purchase for the laser tip because, unlike an ultrasonic tip, the tip cannot be made to drill down into the nucleus to establish and maintain a firm hold on the tissue. The horizontal chopper (e.g., Fine-Nagahara) is then passed into the golden ring and, holding the nucleus by pushing the tip into the sculpted divot, the chopper is brought to the side of the tip. The tip and the chopper are then separated to chop the nucleus. The nucleus is rotated and a second chop is performed to separate a wedge-shaped piece of nucleus, this time using the tip against the proximal edge of the heminucleus and the chopper in the golden ring. Once a wedge of nucleus is liberated, it is held at the tip with the chop instrument, brought up to the iris plane, and emulsified with high frequency laser energy. Utilizing this chop technique, Höh has reported a significant decrease in phaco time as compared with the pilot study (Slide 16).¹¹

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Slide 16

Another version of chopping with the Phacolase involves prechopping the nucleus with the instrument developed by Takayuki Akahoshi. This prechopper can be used to segment the nucleus prior to phacoemulsification with the Phacolase. For denser grades of nuclei, prechopping may provide an advantage in reduced total operating time by eliminating the need for sculpting the small bowl in the nucleus.

Slide 17

Further evolution of technology will likely emphasize separation of irrigation from aspiration and laser in the development of a bimanual technique (Slide 17). For the bimanual technique, Höh has designed a special chopper with an infusion cannula. Because of the absence of risk due to thermal injury, the incision size may effectively be reduced to 1 mm. However, at present, all systems are limited by the incision sizes necessary for IOL implantation.

Phase 3 FDA Clinical Trials are ongoing in the United States. Preliminary data from the multicenter, randomized comparison of Er:YAG with ultrasound phacoemulsification were reported by Packer at the 2001 American Society of Cataract and Refractive Surgery Symposium in San Diego.¹⁹ Three-month follow-up data for 33 patients demonstrated a 1.9% drop in the endothelial cell count for Er:YAG phacoemulsification, versus a 1.7% decline for ultrasound. Intraoperative performance parameters revealed mean energy requirements ranging from 18.3 J for extraction of grade 0 nuclei to 77.8 J for extraction of grade 3 nuclei (Slide 18). The mean laser phacoemulsification time varied from 51.5 seconds for grade 0 to 137.5 seconds for grade 3 nuclei (Slide 19). There was not a great deal of difference in the time required compared with ultrasound for grade 2 nuclei (no grade 3 nuclei had so far been randomized to ultrasound in the study). Of patients undergoing laser phacoemulsification, 92.3% achieved best-corrected visual acuity of 20/40 or better, and 100% achieved best-corrected visual acuity of 20/50 or better.

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Erbium laser phacoemulsification represents an emerging technology with several promising attributes. These include reduction of energy required for phacoemulsification, absence of risk from thermal injury and potential reduction of incision size.

Nd:YAG Laser Phacoemulsification

Dodick Photolysis
Dodick introduced the pulsed Q-switched Nd:YAG in 1991.²⁰ The Nd:YAG laser (1,064 nm) systems employ plasma formation and shock wave generation to produce photolysis of lens material. The shock wave results from the impact of laser radiation on a titanium plate. Alzner has demonstrated that there is no heat production at the laser tip.²¹ As with other nonthermal modalities, the Nd:YAG does not require a cooling sleeve and, therefore, permits cataract extraction through a 1.25-mm incision.

In the Dodick system, laser light does not emerge from the tip. Rather, the shock waves are produced by a titanium block within the tip. Therefore, the eye is not directly exposed to laser energy.

Nd:YAG photolysis represents a low energy modality for cataract extraction. Kanellopoulos reported a mean intraocular energy use of 5.65 J per case.²² This level of energy compares favorably with values previously reported for ultrasound phacoemulsification and approximates the level of energy reported for the choo-choo chop and flip phacoemulsification technique using power modulations.

Surgeons generally use a groove and crack technique with the laser, sculpting in a bimanual fashion and cracking as soon as possible. Alternatively, a prechopping technique may be used as taught by Jack Dodick, MD. Residual fragments are then removed by laser emulsification. The total time that the tip is in the eye varies with the grade of nucleus, from 2.15 minutes for 1+ nuclear sclerosis to 9.8 minutes for 3+ nuclear sclerosis.

The absence of thermal energy and the consequent ability to extract a cataract through an incision of less than 2 mm await the development of IOLs capable of insertion via smaller incisions to achieve a real advantage.

Photon Laser PhacoLysis
The Photon Laser PhacoLysis system (Paradigm Medical, Salt Lake City, Utah) uses an Nd:YAG 1,064-nm laser to produce photo-acoustic ablation of cataract material under aspiration. The ski-shaped distal tip of the probe curves up to intersect the laser light emitted from the optical fiber. The aspiration inlet is placed in the face of the tip, creating a photon trap. Thus, all rays of laser photons that enter the aspiration port are internally reflected and kept within the probe tip. While some minimal heating of tissue occurs, the heat is very rapidly removed by aspiration and the temperature of the probe tip only rises approximately 1° C.

The peak intensity of the Photon Laser PhacoLysis system is more than 10,000 times below that required for the onset of plasma generation, the operative action during posterior capsulotomy. Therefore, the Photon Laser PhacoLysis system represents an exceptionally safe modality in terms of capsular integrity. In the wet lab pig’s eye, one can actually place the anterior lens capsule directly in the line of the laser beam and fire repeatedly without causing any discernible damage to the capsule.

A pilot study with the Photon Laser PhacoLysis system has shown promising results and a clinical study protocol is now underway in the United States. The laser is coupled to the Mentor SIStem (Paradigm) peristaltic I&A pump. The study is restricted to the softer grades of nuclear sclerosis for which this technology is most advantageous.

Sonic Phacoemulsification
The past decade has fostered 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 allowed for this ongoing change in technique by allowing for greater amounts of vacuum to be used in addition to power modulations that have allowed for more efficient utilization of ultrasound energy with greater safety for the delicate intraocular environment.²³

One of the most recent new machines for cataract extraction is the Wave (Staar Surgical). 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.

The Wave contains all of the customary surgical modes routinely used to perform cataract surgery including ultrasound, I&A, vitrectomy, and diathermy. The ultrasound handpiece is a lightweight (2.25 ounces) 2-crystal, 40 kHz piezo electric auto-tuning handpiece that utilizes a load compensating 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 auto-correlation (A/C) 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.

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.²⁴ When incisional burns develop in clear corneal incisions, there may be a loss of self-sealability, corneal edema, and severe induced astigmatism.²⁵ 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 preexisting endothelial dystrophies. Another aspect of current phacoemulsification technology 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 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 kHz to 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 (Slide 20). 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.

Slide 20

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 Hz to 400 Hz. This frequency is 100 to 1,000 times 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 (Slide 21). 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 because intermolecular friction is eliminated (Slide 22). 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.

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Slide 22

The same handpiece and tip can be used 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 the chopping cataract extraction technique that is used in sonic mode can also be used in ultrasonic mode with no discernable difference in efficiency.

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Slide 24

The ideal phacoemulsification machine should offer the highest levels of vacuum possible with total anterior chamber stability. The Wave moves one step closer to this ideal with the advent of their SuperVac tubing (Slide 23). SuperVac tubing increases vacuum capability to up to 650 mm Hg 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 high flow rates such as upon clearance of occlusion of the tip (Slide 24 and Slide 25). This effect only takes place at high flow rates (more than 50 cc/min). The fluid resistance of the SuperVac tubing increases as a function of flow and unoccluded flow is not restricted.

Slide 25

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 uses Windows software and is capable of capturing digitally compressed video displaying the image live on the monitor screen. A 6-gigabyte hard drive can store up to 8 hours of video without the need for videocassette 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 (Slide 26). 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 and 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 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 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.

Slide 26

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 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 through better communication and teaching.

NeoSonix Phacoemulsification
NeoSonix technology represents a hybrid modality involving low frequency oscillatory movement that may be used alone or in combination with standard high frequency ultrasonic phacoemulsification. Softer grades of nuclear sclerosis may be completely addressed with the low frequency modality, while denser grades will likely require the addition of ultrasound. A software upgrade for the Legacy (Alcon) phacoemulsification machine will permit the use of NeoSonix without purchase of additional hardware.

In the NeoSonix mode, the phaco tip has a variable rotational oscillation up to 2°, at 120 Hz. As with sonic phacoemulsification, this lower frequency does not produce significant thermal energy and, therefore, minimizes the risk of thermal injury.

The Legacy may be programmed to initiate NeoSonix at any desired level of ultrasound energy. Thus, the surgeon may use the low frequency mode to burrow into the nucleus for stabilization prior to chopping by setting the lower limit of NeoSonix to 0% phaco power. This approach works best with a straight tip, which acts like an apple corer to impale the nucleus. Alternatively, NeoSonix may be initiated as an adjunct to ultrasound at the 10% or 20% power level.

WhiteStar Technology
WhiteStar represents a new power modulation within ultrasonic phacoemulsification that virtually eliminates the production of thermal energy. Analogous to the ultrapulse mode familiar to users of carbon dioxide lasers, WhiteStar extrapolates pulse mode phacoemulsification to its logical limit. As the duration of the energy pulse is reduced, it will eventually become less than the thermal relaxation time of ocular tissue. Thus it becomes theoretically impossible to produce a corneal wound burn.

White Star technology sets the stage for bimanual cataract extraction with the Sovereign (Allergan) phacoemulsification machine. The absence of thermal energy obviates the need for an irrigation sleeve on the phaco tip, thus permitting reduction of incision size and allowing irrigation through a second instrument, such as an irrigating chopper, placed through the sideport. With an incision size for cataract extraction less than 1 mm, the challenge becomes production of IOLs capable of insertion through such tiny incisions.

Catarex
Vortex phacoemulsification involves placement of a tiny rotary impeller inside the capsular bag through a 1-mm capsulorrhexis. The impeller rotates at 60 kHz and causes expansion of the capsular bag with rotation of the nuclear complex, thus allowing extraction of the cataract from a nearly intact lens capsule. Expansion of the capsular bag minimizes risk of capsular rupture.

The tiny circular capsulorrhexis is constructed with a round diathermy instrument, thus reducing the technical demands of such a surgical feat. The I&A tube containing the rotary impeller is placed over the capsulorrhexis while hydrodissection is performed with gentle irrigation. The tube is then inserted into the capsular bag through the 1-mm capsulorrhexis prior to initiation of rotation, thus, completely isolating the anterior chamber from the activity of cataract extraction. Nuclear material is effectively removed from the capsular bag with vortex action, after which cortex is actually stripped away and extracted.

The advantages of leaving the entire capsular bag in situ following cataract extraction will not be realized until an injectable artificial crystalline lens becomes available. Okahiro Nishi, MD, and others are currently investigating these devices, and may soon have a prototype available.²⁶

Aqualase
Research has led to the development of a fluid-based cataract extraction system. Another nonthermal modality, Aqualase uses pulses of balanced salt solution at 50 Hz to 100 Hz to dissolve the cataract. This modality may potentially demonstrate advantages in terms of safety and prevention of secondary posterior capsular opacification. Still early in its development, Aqualase represents an innovative and potentially advantageous modality for cataract extraction.

Conclusion

Since the time of the inspiration of Charles Kelman, MD, in the dentist’s chair (while having his teeth ultrasonically cleaned), incremental advances in phacoemulsification technology have produced ever-increasing benefits for patients with cataract. The modern, 10-minute procedure simply was not possible a few years ago, and only until recently were prolonged hospital stays common after cataract surgery.

The competitive business environment and the wellspring of human ingenuity continue to demonstrate synergistic activity in the improvement of surgical technique and technology. Future advances in cataract surgery will benefit our patients even further as we develop new phacoemulsification technology.

Video 1

References

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