Laser Cataract Surgery

Laser Cataract Surgery A Prospective Clinical Evaluation of 1000 Consecutive Laser Cataract Procedures Using the Dodick Photolysis Nd:YAG System Anast...
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Laser Cataract Surgery A Prospective Clinical Evaluation of 1000 Consecutive Laser Cataract Procedures Using the Dodick Photolysis Nd:YAG System Anastasios John Kanellopoulos, MD, and the Photolysis Investigative Group Background: To evaluate the safety and efficacy associated with the clinical use of a Q-switched neodymium:yttrium–aluminum– garnet (Nd:YAG) laser for cataract removal. Design: Multicenter, prospective, noncomparative case series. Participants/Intervention: A total of 1000 consecutive eyes underwent cataract extraction with the photolysis Q-switched Nd:YAG laser at 12 international clinical sites. Main Outcome Measures: Visual acuity improvement; total energy used; mean operative time for cataract removal; complications, both intraoperative and postoperative; with a minimum follow-up of 3 months. Results: The mean values were visual acuity improvement from 20/70.2 to 20/24.4. Mean intraocular energy used was 5.65 J per case. Mean operative photolysis time among the surgeons was for up to ⫹1 nuclear sclerosis, 2.15 minutes; up to ⫹2 nuclear sclerosis, 4.8 minutes; and for up to ⫹3 nuclear sclerosis, 9.8 minutes. Three cases were completed by intraocular lens implantation through the original sub-2-mm incision, using a prefolded, by dehydration, acrylic intraocular lens. Minor complications were encountered in 18 cases. Conclusions: These data suggest this photolysis laser technology may be a safe and effective alternative for cataract extraction in human eyes. By use of small clear cornea incisions, the ability to perform cataract extraction and intraocular lens implantation with incisions less than 2 mm has been shown for the first time. Ophthalmology 2001;108:649 – 655 © 2001 by the American Academy of Ophthalmology. Cataract surgery is the most common intraocular surgery and may very well be the most common surgical procedure performed in the United States, with the total number of procedures exceeding 2 million annually.1 It is common knowledge that cataract surgery today is a relatively safe procedure with a low incidence of complications, considering the large number of operations performed. We have previously reported our initial experience with the use of the neodymium:yttrium–aluminum– garnet (Nd:YAG) laser for cataract removal.2 Since that time, this technology has undergone some minor probe design and fluidics improvements. It recently received 510K approval from the Food Originally received: October 25, 1999. Accepted: November 8, 2000. Manuscript no. 99401. From the Department of Ophthalmology, Manhattan Eye, Ear and Throat Hospital, New York, New York, New York University Medical School, New York, New York, and the Ophthalmology Center of Athens, Athens, Greece. Presented in part at the annual meeting of the American Academy of Ophthalmology, Orlando, Florida, October 1999. The author has no financial interest in any of the technologies and/or materials mentioned herein. None of the investigators of the Photolysis Group has any financial interest in this technology with the exception of Dr Dodick. Reprint requests to A. John Kanellopoulos, MD, Manhattan Eye, Ear and Throat Hospital, 539 Park Avenue, New York, New York 10021; website: www.brilliantvision.com © 2001 by the American Academy of Ophthalmology Published by Elsevier Science Inc.

and Drug Administration for clinical use in the Unites States. By use of the same laser source, but using a Qswitched Nd:YAG laser, we conducted a prospective study at the initial 12 international investigative sites of the photolysis system (ARC laser AG, Jona, Switzerland.) With this technology, pulsed laser energy is transferred to the laser probe by means of a quartz fiberoptic. The laser is then focused on a titanium target that exists within the laser tip. Pulsing of the laser produces plasma on the titanium target, which in sequence produces a short acoustic wave that emanates outside the laser tip and is used to emulsify cataract material.3,4

Methods The minor design improvements that this technology has undergone since the original report of the initial 100 cases are noted in Table 1. We evaluated 1000 consecutive patients treated by the original 12 clinical investigators, based in 12 international sites, noted in Table 2. Patient follow-up took place the first postoperative day, the first postoperative week, the first postoperative month, and at 3 months postoperative. Minimum follow-up was 3 months. The inclusion criteria were informed consent and nuclear sclerotic cataract of grade ⫹1 to ⫹4. The study clinical parameters that we evaluated are summarized in Tables 3 and 4: all subjects received informed consent before the procedure; cataract density was rated before surgery ISSN 0161-6420/00/$–see front matter PII S0161-6420(00)00584-4

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Ophthalmology Volume 108, Number 4, April 2001 Table 3. Study Clinical Data

Table 1. Design Improvements to the Dodick Photolysis System Probe 1. Without changing the probe diameter (external diameter of 1.2 mm, internal hollow lumen of 0.9 mm diameter), the quartz fiberoptic has been reduced from a diameter of 470 ␮m to 350 ␮m. 2. The probe opening, initially 0.9 mm in diameter, has been reduced to 0.75 mm. 3. The probe opening angle, initially 25° to the probe’s length, has been increased to 33°. Laser settings 1. The original laser output setting of 12 mJ per pulse remains unchanged, as “high” output setting per pulse. 2. A new lower laser output setting of 7.5 mJ per pulse was introduced as “low” output setting per pulse. Fluidics 1. A Venturi-based aspiration pump (ARC Laser, Jona, Switzerland) combined with a pressurized irrigation system. This system can offer effective irrigation aspiration with aspirating pressures of 300–500 cmHg without anterior chamber collapse.

during slit-lamp biomicroscopy on a ⫹1 to ⫹4 nuclear density scale after pupillary dilatation. It was agreed among all investigators that this scale would represent a clinical spectrum of nuclear cataract density; ⫹4 was the “hardest” nucleus encountered by the clinician and ⫹1 was a mild nuclear sclerosis cataract. All cases in Europe were performed after approval of the College for Human Use by the European Commission (CE Mark). In Saudi Arabia and Mexico, all cases were performed after official Health Ministry approval. In the United States, this technology was not yet approved for clinical use during this study and all cases were performed under an investigative device exemption (IDE) by the Federal Drug Administration.

Operative Technique We have previously described the operative technique used with this technology.2 Between the original 12 surgeons listed herein, the original operative technique has evolved to basically initially sculpting a groove within the lens material using the photolysis probe and irrigation probe in a bimanual fashion, and then cracking the lens as soon as possible. Most cases were performed with topical anesthesia,5 and the others with retrobulbar local block anesthesia. The laser output setting during this phase was 12 mJ per pulse (high setting). After cracking the cataract nucleus, the residual cataract fragments are removed by laser emulsification of the lens. Table 2. Photolysis: Investigators and Sites

1 2 3 4 5 6 7 8 9 10 11 12

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Investigator

City, Country

Jorge Alio-Sanz, MD Egon Alzner, MD Peter Brauweiler, MD Jack Dodick, MD Berthold Eckhardt, MD Akef el-Maghraby, MD Ramon Lorente, MD Potzsch Detlef, MD Jesus Vidaurri-Leal, MD Wolfran Weiner, MD Ivan Zerdab, MD A. John Kanellopoulos, MD

Alicante, Spain Salzburg, Austria Bonn, Germany New York, U.S.A. Bad Hersfeld, Germany Jeddah, Saudi Arabia Orense, Spain Dillingen, Germany Monterey, Mexico Nuremberg, Germany Chambery, France Athens, Greece; New York, U.S.A.

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Informed consent Age Operated eye (right eye or left eye) Cataract density (⫹1 to ⫹4) by slit-lamp biomicroscopy Best-corrected visual acuity preoperatively Intraocular pressure Number of laser pulses Operative time according to nuclear density Intraoperative complications Postoperative complications Postoperative appearance of corneal edema and/or clinical signs of pseudophakic bullous keratopathy Other postoperative complications

The laser output setting during this phase was 7.5 mJ per pulse (low setting). As photolysis time, we defined the “real-time” part of the procedure that the laser probe was present in the anterior chamber. During this time, lens emulsification and aspiration took place. The laser “firing” time represents a much smaller fragment of this “photolysis time” estimated by the number of laser pulses per case multiplied by the 14-ns interval that represents the duration of each pulse (as noted, this Nd:YAG laser is Q-switched). At the conclusion of the cataract removal, all surgeons implanted a foldable posterior chamber intraocular lens, except when intraoperative complications necessitated otherwise. The intraocular lens was implanted by enlarging the original wound to 2.8 to 3.2 mm. The foldable intraocular lenses used in this group of subjects were either the MA60MB (Alcon Laboratories, Inc, Ft. Worth, TX), or the SI-40NB (Allergan Medical Optics, Irvine CA). Of note, there were three cases that, at the conclusion of cataract removal with photolysis, received intraocular lens (IOL) implantation of a prefolded, by dehydration, acrylic lens by one surgeon (AJK). This lens (model H44-1C-1, Acritec, Berlin, Germany) was prefolded to an external diameter of 1.2 to 1.3 mm and then implanted through the original incision used for the photolysis procedure (Figs 1 and 2). The sub-2-mm final intraocular lens implantation opening was confirmed by inability of 1.8-mm wide “spacers” to be placed through the cornea incision after intraocular lens implantation. The postoperative care regimen included a topical fluoroquinolone used four times daily for 1 to 3 weeks, and topical 1% prednisolone acetate used four times daily for 3 to 4 weeks as prophylaxis for postoperative inflammation and infection after clear cornea cataract extraction.6

Results The data by surgeon are summarized in Table 4. A total of 52 cases were completed by conversion to phacoemulsification. This conversion was based on each surgeon’s judgment in regard to the procedure length and the surgeon’s level of comfort with this new technology. It was performed by simply enlarging the original 1.6-mm incision to 2.6- to 3.0-mm to accommodate the surgeon’s preferable phacoemulsification probe. The complications from this group of 1000 cases included 16 cases of intraoperative capsular rupture and two cases of brief intraoperative hyphema. Of the 16 capsular rupture cases, 12 underwent anterior vitrectomy and uneventful posterior chamber IOL placement. Of the remaining four cases, there was no vitreous loss assessed by the surgeon, and a posterior chamber IOL was used to conclude the procedure. With regard to postoperative complications, there was one case of cystoid macular edema at 3 months

Kanellopoulos and the Photolysis Investigative Group 䡠 Laser Cataract Surgery Table 4. Patient Data per Surgeon Investigator 1 2 3 4 5 6 7 8 9 10 11 12

Total cases

1 Nuclear Sclerosis

2 Nuclear Sclerosis

3 Nuclear Sclerosis

45 25 32 8 110 41 110 35 35 269 198 91

28 9 15 15 56 21 61 15 15 140 95 45

12 11 10 5 40 11 35 10 12 90 74 30

5 4 7 2 14 9 14 10 5 37 27 10

No. Intraoperative Complications and Type

No. Postoperative Complications

2 PC 1 PC 1 PBK 1 PC 1 PC 2 transient hyphema from iris injury 1 PC 2 PC (2 AC) 1 Subluxated lens 1 PC 1 PC 2 PC 1 PC 1 PC

Conversion to Phacoemulsification 3 4 4 3 2 6 3 3 4 8 7 5

AC ⫽ anterior chamber; PC ⫽ posterior capsule rupture; PBK ⫽ pseudophakic bullous keratopathy.

after cataract removal (this was an original case of intraoperative posterior capsular rupture and anterior vitrectomy concluded with posterior chamber IOL placement by sulcus fixation). There was one case of pseudophakic bullous keratopathy; this was also one of the cases of intraoperative posterior capsule compromise. At the 3-month follow-up, this subject underwent uneventful penetrating keratoplasty with good visual rehabilitation initially. There was also one case of a subluxated IOL in the postoperative period. This was a case of previous intraoperative posterior capsular rupture that was concluded with posterior chamber IOL placement with sulcus fixation. As mentioned earlier, three photolysis cases were completed with IOL implantation through the original sub-2-mm incisions.

Discussion Increased safety, rapid visual rehabilitation, and maximal subject comfort have been important factors in the development of modern surgical technologies and techniques for cataract extraction.7 Small incisions in modern cataract surgery have driven the development of new phacoemulsifica-

Figure 1. Prefolded, acrylic intraocular lens after photolysis cataract extraction and implantation within the capsular bag through a 1.6-mm incision.

tion tips and probes. We have shown previously that cataract removal with the photolysis laser technology can be safe and effective in removal of softer cataract nuclei.2 The basic mechanism of action of this technology has been previously described as well.3 Each pulse releases 12 mJ of laser energy of a 14-ns duration. The pulsed laser energy has an impact on the titanium target located at the probe tip, which in turn leads to optical breakdown and plasma formation. This creates a shock wave that emanates from the tip in a conelike fashion. These shock waves are used to disturb and emulsify the substance of the cataract. The fragmented particles of the cataract are then aspirated out of the eye through the aspiration port, the lumen of which is also contained in the laser probe. Irrigation takes place through a second probe, which is inserted through a separate corneal incision. Design improvements to the probe, which are summarized in Table 1, include the following. (1) The probe, which has an external diameter of 1.2 mm and an internal hollow lumen of 0.9 mm diameter, has remained unchanged. The enclosed quartz fiberoptic, as mentioned previously, was reduced from the initial 470 ␮m in diameter to a 350-␮m

Figure 2. The same eye illustrated in Figure 1, 30 minutes later during slit-lamp biomicroscopy.

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Ophthalmology Volume 108, Number 4, April 2001 diameter, without reduction of its capacity of laser energy transfer. Therefore, the power settings of laser transfer within this quartz fiberoptic have remained the same, 12 or 7.5 mJ per pulse. The quartz fiberoptic shares the same space with the aspiration lumen. Therefore, by reducing the diameter of the fiberoptic, the functional aspiration lumen diameter has effectively increased, allowing for a greater volume of aspiration to be performed through the same external diameter probe. The probe opening was initially 0.9 mm in diameter. This has been reduced to 0.75 mm in diameter to increase, by the law of Vermoulli, the aspirating pressure at the site of the probe opening. The angle of the probe opening has also been changed. This represents the angle between the probe opening in regard to the rest of the probe, which was initially 25° and was increased to 33° to facilitate better contact between the probe opening and the lens material within the eye. Posterior capsule rupture was encountered in 16 cases. This represents a 1.6% capsular rupture among this group. It should be noted that these 1000 cases of cataract surgery that used this technology represent the initial cases for all 12 surgeons involved, and, therefore, this complication rate includes the “learning curve” with this technology for these surgeons. Nevertheless, the complication rate compares favorably with that encountered with phacoemulsification.8 There were no cases of dropped nuclei or nuclear fragments into the vitreous, and no Descemet’s tears, vitreous hemorrhage, or retinal detachments. It seems that the gradual development of this technology to its wide clinical use among these original 12 clinical investigators improved the safety, efficacy, and time efficiency of the procedure. The operative time required with this technology relies significantly on the ability of the laser/aspirating probe to manipulate the cataract and/or the fragmented cataract pieces. Because it is inherent in the design of this laser probe, it is not possible for the probe to be embedded within the cataract material, as happens routinely with the phacoemulsification probe, facilitating entire nucleus or nucleus fragment manipulation. Therefore, the ability of the probe opening with the assistance of aspiration to “grasp” the nucleus and, more importantly, the nuclear fragments has been essential in the time efficiency and safety involved with this procedure. The introduction of improved fluidics allowing very high aspiration values without anterior chamber collapse and the probe tip improvements mentioned previously have improved efficacy and safety, because the inadvertent “chasing” of the cataract fragment(s) within the anterior chamber with a laser probe could result in an advertent injury to the corneal endothelium with subsequent reduction in endothelial cell count. Therefore, early on when harder “nuclei” (of nuclear sclerosis greater than ⫹1) were removed with this technology, there had been significant effort integrated in the design and development of the probe opening. This was done to increase the aspirating ability of the probe opening, without increasing the probe diameter or reducing the amount of laser energy delivered within each pulse and, therefore, the better “hold” of the entire nucleus or nuclear fragments. The consensus among all investigators is that these probe design changes have increased the overall clinical safety with this

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Table 5. Average Photolysis Time per Surgeon Investigator

No. Cases

Kanellopoulos Weiner Zerdab Eckhardt Lorente Subgroup mean Brauweiler Alzner Potzsch el-Maghraby Vidaurri-Leal Alio-Sanz Dodick Mean

91 269 198 110 110 32 25 35 41 35 45 8

ⴙ1 Nuclear ⴙ2 Nuclear ⴙ3 Nuclear Sclerosis Sclerosis Sclerosis 2 2 2 2 2 2 2 3 2 3 2 2 2 2.15385

4 3 4 4 5 4 5 8 5 6 4 5 5 4.76923

9 6 7 8 10 8 10 15 10 11 12 12 10 9.84615

procedure when nuclei of ⫹1 to ⫹3 nuclear sclerosis were attempted. These developments have also had significant effect on time of the laser emulsification part of these cases. Better manipulation, specifically for nuclei of ⫹2 or greater nuclear sclerosis, has significantly shortened the photolysis time, as evident in Table 5, summarizing the average photolysis time per surgeon according to cataract density. This technology has become the routine choice for cataract removal of lenses of up to ⫹2 nuclear sclerosis among nine of the clinical investigators included in this study. The reason for this preference is the increased sense of surgeon controlled capsular stability originating from improved fluidics and the controlled lens emulsification and aspiration originating from the small pulses of laser-assisted photolysis. Early surgical experience with the photolysis technology in regard to these two key elements along with the small amount of energy used are thought to provide increased safety for softer nuclei among these nine surgeons. It seems that at this stage of development, “harder” cataract nuclei may require longer operative time and therefore the use of phacoemulsification may be preferable in these cases. The mean amount of energy used in this series of subjects was 5.65 J per case. Despite the prolific literature available on phacoemulsification developments and adverse effects, there has been little information published in regard to total phacoemulsification energy used per case. De Bry et al9 report a mean of 782 J ⫾446 for their “phaco-chop” cases in 1998 compared with 3264 J ⫾1218 for their “divide and conquer” technique in a series of 53 eyes. Giers10 reports in a similar recent study a mean energy of 1189 J for “phaco-chop” and 2003 J for “divide and conquer” in phacoemulsification in a series of 200 eyes. These data suggest that Dodick photolysis uses amounts of energy that may be just a small fraction of those routinely used with contemporary phacoemulsification techniques. No measurable heat release is involved with cataract removal with this technology.11 Nevertheless, corneal and scleral burns are a significant concern with contemporary phacoemulsification.12–14 To emulsify a cataract, a phacoemulsification handpiece transforms electrical energy to mechanical energy that vibrates the metal tip and ultrasonic frequency.15 It is the acoustic wave created from the metal

Kanellopoulos and the Photolysis Investigative Group 䡠 Laser Cataract Surgery tip that actually emulsifies the lens. This cascade of energy transfer results in significant heat production that is precipitated by the flow of irrigation fluid around the outside of the needle and aspiration fluid through the needle’s bore. Considering the wide use of phacoemulsification for cataract removal, corneal burns (with potential significant astigmatic changes and corneal endothelial cell compromise, mandating subsequent penetrating keratoplasty) are a significant concern.16 –20 We have shown previously that endothelial cell loss with this technology is confined to 5.7%,2 a rate comparable to modern phacoemulsification. IOL implantation that takes place at the conclusion of the surgery with the Dodick photolysis technology involves enlarging the original incision of about 1.6 mm for a foldable IOL to be implanted. We have concluded three isolated cases with true sub-2-mm intraocular lens implantation for the first time, to the best of our knowledge, demonstrating a potential significant advantage with the use of this technology for cataract extraction over contemporary phacoemulsification techniques. The prefolding technique for this lens has not been described elsewhere. The acrylic lens has the following properties: a 6-mm optic diameter, 12 mm in total diameter, and an A-constant of 119.0. The intraocular lens was prefolded as follows: the lens was dehydrated up to 27%, and the optic of the intraocular lens was rolled onto itself to create a prefolded lens that was a shorter diameter (1.2–1.3 mm). This prefolded IOL will slowly unfold by rehydration in vivo. Three of these lenses were successfully implanted during the course of the study. The prefolded IOL was fully unfolded within the capsular bag less than 30 minutes after implantation in all three subjects (Figs 1 and 2). The use of this technique or other prefolded techniques, and new intraocular lens materials, will complement minute cataract removal by laser. Although cataract surgery performed with phacoemulsification is one of the safest and most effective procedures in medicine, there has been increasing interest in the use of small incisions with the potential goal of performing true endocapsular cataract removal. Retaining the entire capsular bag would open the field for possible injectable materials that could act as an intraocular lens by filling the capsular bag and possibly retaining accommodation. Recently, some of these entities have been shown to be possible in laboratory animals.21 Phacoemulsification probes are limited to a certain diameter because of a necessary cooling sleeve that accompanies the ultrasound needle.

Conclusion Further studies are necessary to evaluate the safety and efficacy of these principles in human eyes. We have found in this limited noncontrolled study among several surgeons that Dodick photolysis may be a safe and effective alternative technology for laser cataract removal. It seems to use significantly less energy compared with phacoemulsification and may have fewer complications than phacoemulsification in regard to inadvertent intraoperative heat release. The time efficiency of this technology has improved dra-

matically with small design improvements in the laser probe and settings, and we have shown by use of this technology that cataract extraction, as well as IOL implantation with incisions less than 2 mm, is now possible in human eyes. Acknowledgment. The author acknowledges the technical assistance and guidance of Mr Reinhardt Thyzel and Dr Kristine Kreiner for their technical knowledge of lasers, fluidics, and intraocular lenses that contributed enormously in probe, intraocular lens, and technique development.

Appendix The Photolysis Investigative Group: Jorge Alio-Sanz, MD, Alicante, Spain; Egon Alzner, MD, Salzburg, Austria; Peter Brauweiler, MD, Bonn, Germany; Jack M. Dodick, MD, New York, New York; Berthold Eckhardt, MD, Bad Hersfeld, Germany; Akef elMaghraby, MD, Jeddah, Saudi Arabia; Ramon Lorente, MD, Orense, Spain; Potzsch Detlef, MD, Dillingen, Germany; Jesus Vidaurri-Leal, MD, Monterey, Mexico; Wolfran Weiner, MD, Nuremberg, Germany; Ivan Zerdab, MD, Chambery, France; and A. John Kanellopoulos, MD, New York, New York and Athens, Greece.

References 1. American Academy of Ophthalmology. Preferred Practice Pattern. Cataract in the Adult Eye. San Francisco, CA: American Academy of Ophthalmology, 1996. 2. Kanellopoulos AJ, Dodick JM, Brauweiler P, Alzner E. Dodick photolysis for cataract surgery: early experience with the Q-switched neodymium:YAG laser in 100 consecutive patients. Ophthalmology 1999;106:2197–202. 3. Dodick JM, Sperber LTD, Lally JM. Neodymium:YAG laser phacolysis of the human cataractous lens [letter]. Arch Ophthalmol 1993;111:903– 4. 4. 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. Possible implications for Nd:YAG laser phacolysis of the cataractous human lens. J Cataract Refract Surg 1991;17: 794 –7. 5. Gills JP, Cherchio M, Raanan MG. Unpreserved lidocaine to control discomfort during cataract surgery using topical anesthesia. J Cataract Refract Surg 1997;23:545–50. 6. Kanellopoulos AJ, Dreyer EB. Postoperative infection following current cataract extraction surgery. Int Ophthalmol Clin 1996;36:97–107. 7. Leaming DV. Practice styles and preferences of ASCRS members—1998 survey. J Cataract Refract Surg 1999;25:851–9. 8. Cionni RJ, Osher RH. Intraoperative complications of phacoemulsification surgery. In: Steinert RF, ed. Cataract Surgery: Technique, Complications, and Management. Philadelphia, W. B. Saunders, 1995; 327– 40. 9. 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 –92. 10. Giers U. Phako-Chop verringert Ultraschallenergie auf 60% des Ausgangswertes. Ophthalmo-Chirurgie 1998;10:197–203. 11. Alzner E, Grabner G. Dodick laser phacolysis: thermal effects. J Cataract Refract Surg 1999;25:800 –3.

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Ophthalmology Volume 108, Number 4, April 2001 12. Mackool RJ. Preventing incision burn during phacoemulsification [letter]. J Cataract Refract Surg 1994;20:367– 8. 13. Scleral and corneal burns during phacoemulsification with viscoelastic materials. Health Devices 1988;17:377–9. 14. Polack FM, Sugar A. The phacoemulsification procedure. III. Corneal complications. Invest Ophthalmol Vis Sci 1977;16:39–46. 15. Kelman CD. Phaco-emulsification and aspiration. A new technique for cataract removal. A preliminary report. Am J Ophthalmol 1967;64:23–35. 16. Zetterstrom C, Laurell CG. Comparison of endothelial cell loss and phacoemulsification energy during endocapsular phacoemulsification surgery. J Cataract Refract Surg 1995;21: 55– 8.

17. Davis PR. Phaco transducers: basic principles in corneal thermal injury. Eur J Implant Refract Surg 1993;5:109 –12. 18. Benolken RM, Emery JM, Landis DJ. Temperature profiles in anterior chamber during phacoemulsification. Invest Ophthalmol 1974;13:71– 4. 19. Polack FM, Sugar A. The phacoemulsification procedure. II. Corneal endothelial changes. Invest Ophthalmol 1976;15: 458 – 69. 20. Sugar A, Schertzer, R. Clinical course of phacoemulsification wound burns. J Cataract Refract Surg 1999;25:688 –92. 21. Nishi O, Nishi K, Mano C, et al. Lens refilling with injectable silicone in rabbit eyes. J Cataract Refract Surg 1998;24:975– 82.

Discussion by Richard J. Mackool, MD This is a prospective study in which surgeons who most certainly were skilled in phacoemulsification utilized yttrium–aluminum– garnet (YAG) laser-induced acoustic energy to remove cataracts. The patients were selected, and had cataracts which would be considered to be routine, i.e., not dense, and presumably with deep anterior chambers and well-dilated pupils. Corneal endothelial cell loss in the study group was reported to be 5.57% at a minimum of 3 months after surgery. While this is an acceptable level, it is probably greater than that which would have been expected to occur after phacoemulsification because more than half of these patients had only 1⫹ nuclear sclerosis or less and no patients had 4⫹ nuclear sclerosis. Furthermore, it may take 1 year or more for the endothelial cell concentration to equilibrate over the posterior corneal surface, and endothelial loss measured at 1 year might be greater than 5.57%. In contrast, endothelial loss with phacoemulsification on non-selected patients has been as low as 2.9% at 1 year. Therefore, although mean intraocular energy used was low (5.7 joules), endothelial cell loss rates did not seem to benefit from this. If corneal cell loss was somewhat higher than expected and mean intraocular energy used was low, what other factors may have caused the endothelial cell attrition? Mean operative photolysis time was 2.15 minutes for up to 1⫹ nuclear sclerosis, 4.8 minutes for up to 2⫹ nuclear sclerosis, and 9.8 minutes for up to 3⫹ nuclear sclerosis. These times are certainly much longer than those typically required for nucleus removal by ultrasonic energy in similar eyes, and this relatively slow rate of nucleus removal apparently caused the investigators to avoid performing laser photolysis on lenses which were rated as 4⫹ nuclear density. Total flow through the eye is not reported, but such flow is certainly proportional to the time spent performing nucleus removal. The relatively slow rate of nucleus removal in these eyes may therefore have required greater flow and this may in turn have resulted in greater endothelial cell loss. In addition, inability to penetrate and hold the nucleus and/or nuclear segments was reported. This would not result in difficulty during nucleus sculpting, but could easily result in greater manipulation and particle movement during attempts to remove segments of nucleus. Greater endothelial cell loss would be expected in such situations. The author reports that improved fluidics have been added to the system in an attempt to overcome such difficulties; perhaps this will be beneficial.

From the The Mackool Eye Institute, Astoria, New York, and The New York Eye & Ear Infirmary, New York, New York. Address correspondence to Richard J. Mackool, MD, The Mackool Eye Institute & Laser Center, 31-27 41st Street, Astoria, NY 11103.

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Fifty-two eyes (5.2%) required conversion to phacoemulsification. The indication for conversion is not given, but it seems likely that failure to achieve a satisfactory rate of nucleus removal was the cause. Were these 52 eyes all within the 3⫹ nuclear sclerosis group? If so this would represent approximately 41% of the 128 eyes in this group, and could well mean that this technology was reasonably successful only in eyes with no greater than 2⫹ nuclear sclerosis. With regard to the potential benefit of reduced incision size, the minimum incision size required for the insertion of a 1.2 mm diameter probe is 1.8 mm. The result, however, would be an extremely tight incision which could make it difficult to advance, retract or angle the probe, and cause radiating corneal striae. Such problems are routinely encountered when round, rigid instruments are inserted through extremely tight incisions. In comparison, current phacoemulsification instruments are generally inserted through larger incisions which vary between 2.5 and 3.0 mm. However, the YAG photolysis system also requires a separate incision for the delivery of infusion. If an 18-gauge infusion cannula is utilized, as is currently done, another 1.8 mm incision is required. This incision is permitted to be tight, if manipulation of the probe is not required. However, if the probe is to be used as a second instrument in order to position nuclear particles, a somewhat larger incision may be needed in order to prevent the problems described above. When one factor in the small sideport incision which is normally used during phacoemulsification procedures (approximately 0.5–1.0 mm external width tapering to 0.2– 0.4 mm internal width), the sum of the 2 incisions required to perform either phacoemulsification or YAG photolysis is comparable. There has been much discussion of the potential goal of performing true endocapsular cataract removal in order to retain virtually the entire capsular bag for possible injection of materials which could act to create an accommodative lens. This technique requires delivery of infusion into the capsular sac in order to keep it inflated during the lens removal process, as collapse of the sac during the process will result in capsular rupture when the capsule inevitably contacts the activated laser or ultrasonic probe. Laser photolysis, if used to perform endocapsular cataract removal, will therefore require either a second opening into the capsular sac to deliver infusion, or an infusion sleeve which would be similar in diameter to that required by phacoemulsification equipment. If either of these technical options are employed, adequate preservation of the capsular sac may not be achievable. Will reduction in potential for corneal incision burn differentiate laser photolysis from phacoemulsification? This is difficult to