Photolysis using the dodick–ARC laser system for cataract surgery1

Photolysis using the Dodick–ARC laser system for cataract surgery Werner W. Huetz, MD, H. Berthold Eckhardt, MD ABSTRACT Purpose: To report the intraoperative and postoperative results of cataract surgery using a pulsed Q-switched neodymium:YAG (Nd:YAG) laser. Setting: Eye Clinic, Kreiskrankenhaus Bad Hersfeld, Germany. Methods: This prospective study involved 100 consecutive patients who had cataract surgery between October 1998 and May 1999. The patients were allocated to 3 groups based on the hardness of the nucleus using the LOCS III system: Group 1 (NO ⱕ 2.9), 48 patients; Group 2 (NO 3.0 to 3.9), 46 patients; Group 3 (NO ⱖ 4.0), 6 patients. Plasma was generated with a pulsed Q-switched Nd:YAG laser (ARC GmbH). A clear corneal incision of 1.25 mm provided access for the laser tip. An intraocular lens (CeeOn姞 Edge [Pharmacia & Upjohn] or AcrySof姞 [Alcon]) was implanted via a separate clear corneal incision. Intraoperative laser pulse rate and total energy were recorded. Preoperative and postoperative (2 days and 6 months) central cornea thickness was compared. Results: In all cases, the cataract was removed within an acceptable time without converting to the conventional phacoemulsification technique. Mean total energy was 1.97 J ⫾ 1.43 (SD) in Group 1, 3.37 ⫾ 1.59 J in Group 2, and 7.70 ⫾ 2.09 J in Group 3. No significant postoperative changes between preoperative and postoperative central pachymetry were seen in Groups 1 and 2; there was a 1.9% postoperative increase in central pachymetry in Group 3. This could be a consequence of the higher volume of intraoperative balanced salt solution and the prolonged procedure in this group. Six months postoperatively, there were no significant changes from the preoperative values. Conclusion: Photolysis of the lens nucleus can be used safely and efficiently for nuclei with a hardness up to NO 3.9. The energy required for lens removal was 83% less than that required by phacoemulsification. J Cataract Refract Surg 2001; 27: 208 –212 © 2001 ASCRS and ESCRS

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ontinuous development of the ophthalmological laser (excimer, picosecond, and nanosecond) has

Accepted for publication July 24, 2000. From Eye Clinic, Kreiskrankenhaus Bad Hersfeld, Bad Hersfeld, Germany. Neither author has a financial interest in any product mentioned. Reprint requests to Werner W. Huetz, MD, Eye Clinic, Kreiskrankenhaus Bad Hersfeld, 36251 Bad Hersfeld, Germany. © 2001 ASCRS and ESCRS Published by Elsevier Science Inc.

made the use of laser systems in cataract surgery likely. The first attempts to extract cataracts by a laser technique were performed about 10 years ago but were not continued because of technical problems and considerable risks (eg, scattered laser beam). In 1991, Dodick introduced a procedure in which a pulsed Q-switched neodymium:YAG (Nd:YAG) laser (1064 nm) generated plasma.1,2 The resulting shock waves were used to fragment the lens nucleus of cataract patients (Dodick photolysis).3 Two aspects of this tech0886-3350/01/$–see front matter PII S0886-3350(00)00693-3

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nique are interesting: Photolysis appears to need much less energy than phacoemulsification, and the required incision size is smaller. The latter may become increasingly important with the development of injectable lens material. Today, 2 laser systems with different physical principles are available for lens removal. The Nd:YAG laser (1064 nm), which is used for photolysis, works with plasma formation and shock-wave generation, derived from experience with the Nd:YAG laser capsulotomy.4 The absorption of the erbium:YAG laser (2940 nm) in aqueous tissue leads to immediate evaporation, with consequent loosening of the surrounding tissue.5,6 The aim of this study was to prove the clinical applicability of laser cataract surgery. We report the results of cataract surgery using the Nd:YAG laser in a clinical trial with a 6 month follow-up.

Patients and Methods Between October 1998 and May 1999, 100 eyes of 100 patients had cataract surgery with the photolysis procedure1 using an Nd:YAG laser (ARC GmbH). Preoperatively, all patients had a complete eye examination comprising distance vision, intraocular pressure (IOP) measurement, slitlamp examination of the anterior eye segment, and central pachymetry of the cornea. Corneal thickness was measured with the Tomey pachymeter SP 2000. Calculations were based on the mean of 9 measurements. Preoperative and postoperative (2 days and 6 months) central corneal pachymetry data were compared. To classify the cataracts in a practical and reproducible way, the nuclear opacity (NO) as a measure of nucleus hardness was chosen from the LOCS III system described and modified by Chylack et al.7 Patients were allocated to 3 groups: Group 1, NO ⱕ 2.9, 48 patients; Group 2, NO 3.0 to 3.9, 46 patients; Group 3, NO ⱖ 4.0, 6 patients. Glaucoma suspects and patients with corneal pathology or a history of uveitis or retinal disorders were excluded. Neodymium:YAG Laser Laser pulses were generated with a Q-switched Nd: YAG laser (wavelength 1064 nm) emitting single pulses with a maximum pulse energy of 10 mJ and a pulse duration of 12 nanoseconds in a frequency of 1 to10 Hz.

Laser pulses were routed via a flexible 340 ␮m quartz fiber through the aspiration port of a special laser handpiece and focused on a 45 degree bent titanium platelet to induce optical breakdown with a defined shock wave. The distance between the end of the quartz fiber and the titanium platelet was 1.3 mm. The nucleus fragments were continuously aspirated through a 0.45 mm port in the laser handpiece by a Geuder Megatron irrigation/ aspiration unit. Irrigation was performed with a separate handpiece. Surgical Technique After a 3.2 mm clear corneal incision for intraocular lens (IOL) implantation was prepared, 19 gauge paracenteses were positioned at 12 and 6 o’clock. The anterior chamber was filled with a viscoelastic agent (sodium hyaluronate, Healon威), and then a 5.0 mm continuous curvilinear capsulorhexis was performed with a cystotome, followed by hydrodissection and hydrodelineation of the lens cortex and nucleus. During the bimanual photolysis, irrigation was performed with a 1.25 mm (outer diameter) modified irrigation cannula, whereas the 1.25 mm diameter laser and aspiration handpiece was used during photolysis/photofragmentation and aspiration of lens fragments through the second paracentesis. After the superficial cortex material was aspirated with the laser handpiece, photolysis of the lens nucleus was performed. The bimanual technique of photoablation and fragmentation of the nucleus is preferred in our clinic. The laser tip should touch only the nucleus surface and not dig into the lens. After central photofragmentation, the lens nucleus is handled bimanually, similar to the divide-and-conquer technique. After further lysis and fragmentation, the nucleus fragments are aspirated. The laser repetition frequency used for photolysis was 2 Hz. To aspirate lens nucleus fragments via the ARC laser handpiece and the Geuder Megatron unit, a variable vacuum up to 400 mm Hg and a flow of 21 mL/minute can be used. The “pseudo-Venturi” effect of the system was used to improve the aspiration power and speed up the procedure. Remaining cortex residues were also removed with the laser handpiece or a special aspiration handpiece adapted to the 19 gauge paracentesis. After the anterior chamber was filled with Healon, a foldable silicone lens (CeeOn威 Edge, Pharmacia & Upjohn, 50

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patients) or a hydrophobic acrylic lens (ArcySof威, Alcon, 50 patients) was implanted. The viscoelastic substance was carefully removed from the anterior chamber and the capsular bag. After the anterior chamber was filled with balanced salt solution, the paracenteses were also hydrated with balanced salt solution. The energy required intraoperatively for lens removal was calculated by the number of laser pulses that were needed for lysis of the lens nucleus. The time for removal of the lens nucleus and cortex (measured in 15 second intervals) as well as the balanced salt solution volume, which passed through the eye, was documented. Postoperatively, patients received gentamicin 4 times daily for 1 week as well as prednisolone acetate 1.2 mg (Inflanefran威) and nonsteroidal antiphlogistic eyedrops (indomethacin 10 mg, Chibro-Amuno 3威) 4 times daily for 2 months. Simstat威 for Windows was used for statistical evaluation of the clinical trial data on a personal computer.

Results In Group 1, the mean age of the 31 women was 69.7 years and of the 17 men, 58.0 years. In Group 2, the mean age of the 26 women was 57.0 years and of the 20 men, 67.5 years. In Group 3, the mean age of the 3 women was 84.0 years and of the 3 men, 76.0 years. To remove the lens nucleus and cortex completely, 207.90 ⫾ 150.50 pulses were needed in Group 1, 359.00 ⫾ 168.00 pulses were needed in Group 2, and 813.00 ⫾ 2.22 pulses were needed in Group 3. With an energy of 10 mJ per pulse at an efficiency of 95%, the mean applied energy was 1.97 ⫾ 1.43 J in Group 1, 3.37 ⫾ 1.59 J in Group 2, and 7.70 ⫾ 2.09 J in Group 3. The required energy differed significantly among the 3 groups (P ⬍ .005). Balanced salt solution consumption varied considerably: 177.3 ⫾ 66.7 mL in Group 1, 291.0 ⫾ 71.7 mL in Group 2, and 380.0 ⫾ 33.7 mL in Group 3. Complete cataract removal (lysis and apiration) lasted 4.75 ⫾ 1.50 minutes in Group 1, 7.25 ⫾ 1.75 minutes in Group 2, and 10.50 ⫾ 1.50 minutes in Group 3. In Group 1, mean central corneal thickness was 578.8 ⫾ 27.0 ␮m preoperatively, 579.4 ⫾ 26.6 ␮m on 210

the second postoperative day, and 578.3 ⫾ 26.8 ␮m after 6 months. Neither postoperative change was significantly different from the preoperative thickness (P ⬎ .05). In Group 2, mean central corneal thickness was 578.6 ⫾ 26.9 ␮m preoperatively, 579.3 ⫾ 27.2 ␮m in the early postoperative phase, and 578.7 ⫾ 26.6 ␮m at the end of the follow-up. Neither postoperative change was significantly different from the preoperative measurement (P ⬎ .05). In Group 3, mean central corneal thickness was 597.2 ⫾ 29 ␮m preoperatively and 608.2 ⫾ 20.3 ␮m on the second postoperative day; this change was significant (P ⬍ .05). Six months postoperatively, mean corneal thickness was 595.1 ⫾ 18.0 ␮m, which was not significantly different from the preoperative measurement (P ⬎ .05). Baseline IOP (mean 15.4 ⫾ 2.1 mm Hg; median 15.0 mm Hg) did not change significantly in any group on the second postoperative day (mean 15.3 ⫾ 3.5 mm Hg; median 15.0 mm Hg) or after 6 months (mean 16.5 ⫾ 2.1 mm Hg; median 16.0 mm Hg). In Group 1, the best corrected visual acuity (BCVA) improved from 0.32 (median) at baseline to 0.63 on the second postoperative day and 0.80 after 6 months. In Group 2, BCVA improved from 0.32 (median) to 0.50 immediately after surgery and 0.63 at the end of followup. The lowest preoperative BCVA, 0.20 (median), was in Group 3. On the second postoperative day, it improved to 0.40 (median), and at the end of follow-up, to 0.63 (median). The BCVA did not worsen in any patient after photolysis.

Discussion We believe this is the first report of the use of an Nd:YAG laser for cataract removal with a 6 month follow-up. The Nd:YAG laser (1064 nm) uses the mechanism of plasma formation and shock-wave formation, derived from experience with the Nd:YAG capsulotomy.4 During capsulotomy as well as during photolysis, the shock wave alters the tissue. The shock wave is formed when the radiation of the Nd:YAG laser hits its target; in a capsulotomy, the target is the posterior lens capsule, and in photolysis, the target is a titanium platelet that releases plasma formation after being hit by radiation.2,8

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In vitro investigations by Alzner and coauthors9 show that in contrast to conventional ultrasound phacoemulsification, Nd:YAG laser photolysis involves no risk of focal tissue heating.9,10 Even under low or no flow, there is no heating at the laser tip.9 This is the first advantage of this Nd:YAG laser technique. Since there is no risk of focal tissue heating, no permanent cooling of the laser tip is required. The laser extension therefore needs a diameter of only 1.25 mm to contain the laser fiber (0.34 mm diameter) as well as the aspiration port. This leads to less surgical trauma during nucleus and cortex removal than in conventional phacoemulsification (incision size 2.8 to 3.2 mm). Appropriate IOLs to take advantage of the minimal size incision technique will soon be available. Unlike in other laser systems that are used for cataract surgery,5,11,12 the laser beam does not emerge from the handpiece during photolysis. Plasma is generated and transformed into kinetic energy within the handpiece.3 These shock waves result in focal disruption of the lens into pieces that can be aspirated. The eye is not directly exposed to the laser beam. At present, each laser handpiece is produced individually for each surgeon. The titanium platelet is worn out by the plasma generation at the tip of the handpiece. The manufacturer states that the laser tip can perform with up to 1500 pulses. In our study, we did not need more than 1200 pulses for any procedure. Multiple use of laser probes after sterilization may therefore be possible. To maintain baseline conditions in this study, a new handpiece was used for each procedure. In the future, disposable laser probes will be available and inexpensive. The release of metal particles during phacoemulsification has been reported.13–15 This might occur with Nd:YAG photolysis since the laser beam hits the titanium platelet and material is abraded. However, none of the postoperative examinations found intraocular metal particles such as those found after phacoemulsification. The third advantage of this technique is the reduction of energy necessary for cataract removal. With our surgical technique, lens removal required between 41 and 1135 laser pulses. Based on a 5% loss of efficiency during transformation from laser radiation into kinetic energy, this corresponds to a total energy load of 0.38 to 9.79 J to the eye. A simplified calculation for the energy used during phacoemulsification reveals the following: With a device

output of approximately 50 W, an efficiency of 5.0% (transformation from electric energy into ultrasound energy), and a 7.5% thermal transfer from the piezo crystal to the tip, the energy delivered to the eye amounts to 6 W/second. If we consider the phaco power to be 100% and the surgical time 10 seconds, the result is delivery of 60 J to the eye. Reports16 of an average of 3264 ⫾ 1218 J for standard phacoemulsification using the divide-and-conquer technique or 782 ⫾ 446 J for the phaco-chop technique seem to be based on only the energy used to generate ultrasound, although this is not mentioned specifically. In our study using photolysis with a maximum rate of 1135 pulses, the eye received only 9.79 J. This is 83% less energy than in phacoemulsification. According to the literature,5 the energy released in the eye during the erbium laser technique in 100 Hz mode at 10 mJ/pulse and a mean surgical time of 150 seconds is 150 J, which is 15 times higher than the energy released in photolysis. The postoperative alteration of corneal thickness can be used as an indicator of corneal endothelial cell damage, according to Kohlhaas and coauthors.17 After phacoemulsification and posterior chamber lens implantation, increases in central corneal thickness of 5% to 12% have been seen.18 In our study, no significant increase in central corneal thickness was observed in Groups 1 and 2 with nucleus hardness up to NO 3.9. The increase in central corneal thickness in Group 3 (NO ⱖ 4.0) immediately after surgery correlated with a longer surgical time and a higher irrigation volume. No significant changes from the preoperative thickness19,20 were found during the last examinations after 6 months. Postoperative refraction, visual acuity, and IOP were comparable to the findings after ultrasound phacoemulsification.5,21–23 Our promising postoperative results underscore the impression of minimal tissue trauma, particularly considering the learning curve, during the course of our study. The photolysis technique offers a technically new procedure for experienced surgeons that can be safely and efficiently used at this stage of development for nuclei with a hardness of up to NO 3.9. The energy required for lens removal with photolysis is 6 times less than that with phacoemulsification. If the nucleus hardness exceeds NO ⱖ 4.0, a sufficient ablation is possible

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but time consuming, and, at the present stage of development, uncomfortable. Modifications of the laser tip and the surgical technique may lead to further improvements.

References 1. Dodick JM. Laser phacolysis of the human cataractous lens. Dev Ophthalmol 1991; 22:58 – 64 2. Dodick JM, Christiansen J. Experimental studies on the development and propagation of shock waves created by the interaction of short Nd:YAG laser pulses with a titanium target. J Cataract Refract Surg 1991; 17:794 –797 3. Dodick JM, Lally JM, Sperber LTD. Lasers in cataract surgery. Curr Opin Ophthalmol 1993; 4(1):107–109 4. Aron-Rosa D, Aron J-J, Griesemann M, Thyzel R. Use of the neodymium-YAG laser to open the posterior capsule after lens implant surgery: a preliminary report. Am Intra-Ocular Implant Soc J 1980; 6:352–354 5. Ho¨h H, Fischer E. Erbiumlaserphakoemulsifikation— Eine klinische Pilotstudie. Klin Monatsbl Augenheilkd 1999; 214:203–210 6. Wetzel W, Brinkmann R, Koop N, et al. Photofragmentation of lens nuclei using the Er:YAG laser: preliminary report of an in vitro study. Ger J Ophthalmol 1996; 5:281–284 7. Chylack LT Jr, Wolfe JK, Singer DM, et al. The Lens Opacities Classification system III. Arch Ophthalmol 1993; 111:831– 836 8. Sperber LTD, Dodick JM. Laser therapy in cataract surgery. Curr Opin Ophthalmol 1995; 6(1):22–26 9. Alzner E, Dodick JM, Thyzel R, Grabner G. Experimentelle Laser-Phakolyse mit dem ARC-Puls-Nd-YAG-Laser. Spektrum Augenheilkd 1998; 12:24 –27 10. Alzner E, Grabner G. Dodick laser phacolysis: thermal effects. J Cataract Refract Surg 1999; 25:800 – 803 11. Berger JW, Talamo JH, LaMarche KJ, et al. Temperature measurements during phacoemulsification and erbium: YAG laser phacoablation in model systems. J Cataract Refract Surg 1996; 22:372–378 12. Neubaur CC, Stevens G Jr. Erbium:YAG laser cataract removal: role of fiber-optic delivery system. J Cataract Refract Surg 1999; 25:514 –520

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13. Braunstein RE, Cotliar AM, Wirostko BM, Gorman BD. Intraocular metallic-appearing foreign bodies after phacoemulsification. J Cataract Refract Surg 1996; 22: 1247–1250 14. Dunbar CM, Goble RR, Gregory DW, Church WC. Intraocular deposition of metallic fragments during phacoemulsification: possible causes and effects. Eye 1995; 9:434 – 436 15. Martı´nez-Toldos JJ, Elvira JC, Hueso JR, et al. Metallic fragment deposits during phacoemulsification. J Cataract Refract Surg 1998; 24:1256 –1260 16. DeBry P, Olson RJ, Crandall AS. Comparison of energy required for phaco-chop and divide and conquer phacoemulsification. J Cataract Refract Surg 1998; 24:689 – 692 17. Kohlhaas M, Stahlhut O, Tholuck J, Richard G. Entwicklung der Hornhautdicke und – endothelzelldichte nach Kataraktextraktion mittels Phakoemulsifikation. Ophthalmologe 1997; 94:515–518 18. Zetterstro¨m C, Laurell C-G. Comparison of endothelial cell loss and phacoemulsification energy during endocapsular phacoemulsification surgery. J Cataract Refract Surg 1995; 21:55–58 19. Amon M, Menapace R, Scheidel W. Results of corneal pachymetry after small-incision hydrogel lens implantation and scleral-step incision poly(methyl methacrylate) lens implantation following phacoemulsification. J Cataract Refract Surg 1991; 17:466 – 470 20. Cheng H, Bates AK, Wood L, McPherson K. Positive correlation of corneal thickness and endothelial cell loss; serial measurements after cataract surgery. Arch Ophthalmol 1988; 106:920 –922 21. Barak A, Desatnik H, Ma-Naim T, et al. Early postoperative intraocular pressure pattern in glaucomatous and nonglaucomatous patients. J Cataract Refract Surg 1996; 22:607– 611 22. Kammann J, Dornbach G, Cosmar E. 2 Jahre Kleinschnittchirurgie; Ergebnisse und Indikationen. Ophthalmologe 1995; 92:266 –296 23. Jahn CE. Senkung des intraokularen Drucks durch Phakoemulsifikation und Hinterkammerlinsenimplantation. Ophthalmologe 1995; 92:560 –563

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