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Neodymium:YAG laser damage of intraocular lenses
Neodymium: YAG laser damage of intraocular lenses S. Gregory Smith, M.D., Frank M. Snowden, Ph.D.
B TR T Intraocular I n e s (I OL ') 'uitable for implantation ~ ere anal zed for the pre ence of refractil parti I . The e, ere found in lathe-cut and injection-molded len e from ariou manufacturers. A YAG la er wa foeu ed 2 mm bond the IOL in a p cial te t chamber and fired throu h th m. The IOL were then anal zed for damage. A photographicall documented ·tud of i IOL u ing Q-S\ itched and mode-locked la er how d optical breakdown occurring within the IOL . this \ a not cI arl r lated to J'efractile particle . Optical breakdo\ n did not occur in t\ 0 IOL ,ith a imiJar number of refractile particl . Dama e wa 'een \ ith the mode-locked but n t \ ith the Q- witch d la r. Th optical breakdown occurred more frequ ntl at high pow r (5.0 mJ) than at 10\ power (1.2 mJ).
Ke Word ,: intra cular I n spitting , mod lo·k d l a ' r,Q- 'witch d la ' r r fractil partie1 .
Refractile particles within intraocular lenses (IOLs) were initially noted by Pearce (personal communication) as well as by Ballin (Ocular Surgery News, October 15, 1985, page 14) and Bath.I Pearce and Ballin noted the particles in injection-molded lenses but saw few in lenses manufactured by other techniques. Bath noted particles in all IOL types. One author (SGS) noted a case in which optical breakdown by YAG laser energy occurred within the anterior portion of the IOL optic when the laser appeared to be focused on a point within the vitreous. This observation raised several questions. Was this a correct observation or was it surgeon error? Was it related to the refractile particles? Was it related to the YAG laser? Was it related to the manufacturing technique of the IOL? Was it caused by some other etiology? This study was designed to answer these questions.
MATERIALS AND METHODS Six IOLs that had been approved for implantation were taken from the hospital shelf and examined at the slitlamp and graded for refractile particles. A refractile particle was defined as an area of optical distortion within the IOL optic. On slitlamp examination, refractile particles are seen in oblique illumination and are not visible when a red reflex is present. The majority appear white although some may be red. They may vary in size but are quite small, as seen in Figure 1. After the slitlamp examination, each IOL was placed in a specially constructed test chamber (Figure 2). This chamber had a flat glass anterior surface, an anterior chamber, a micrometer-controlled IOL-holding device that adjusted in an anterior-posterior direction, and a posterior cham ber. This device was affixed to the laser's chin rest, and the entire test chamber containing the
From the General Ophthalmology Service, Wills Eye Hospital, Philadelphia. Pennsylvania, the Department of Ophthalmology, Hershey Medical Center, Hershey, Pennsylvania (Dr. Smith); the 3M Vision CarelIOL Department, Health Care Enterprises Division, and Biosciences Laboratory (Dr. Snowden). Supported ill part by all unrestricted grant from 3M Vision Care. Presented in part at the Symposium on Cataract, IOL and Refractive Surgery, Los Angeles, April 1986. The authors have no proprietary interest in any IOL design. Reprillt requests to S. Gregory Smith, M.D., 1700 Shallcross Avellue, Suite 2, Wilmington, Delaware 19806. 660
J CATARACT REFRACT
SURG-VOL 14, NOVEMBER 1988
Fig. 1.
(Smith) Intraocular lens positioned within test chamber.
IOL was moved horizontally by the micrometer (Figure 3). The posterior surface of the IOL was marked with a scratch and placed in the device, which was mounted on a mode-locked laser (Medical Laser, Inc.). The laser was focused on the scratch and the slitlamp was locked. The IOL was then moved 2 mm anterior to the focus point by the micrometer. The laser was fired through the IOL while it was moved horizontally by the second micrometer on the device. Three lines of laser treatment were delivered at power settings of l.2 m} (60 bursts), 5.0 m} (70 bursts), and l.2 m} (75 bursts). The device was then mounted on a Q-switched laser (Coherent) and the same treatment was given to the bottom half ofthe IOL. It was not removed from the device between treatment with each laser. These power settings were fixed on the modelocked laser and were duplicated on the Q-switched
Fig. 2.
laser. The IOLs were then removed from the chamber, examined for pits, and photographed. RESULTS Photography of the refractile particles was difficult both in vivo and in vitro. Figure 1 demonstrates refractile particles within a human eye. This was graded as + + +. Figure 4 demonstrates refractile particles in an injection-molded lens graded as + + . Table 1 shows the grading of the IOLs and the results of the laser treatments. It reveals that the Q-switched laser did not cause IOL damage. With the mode-locked laser, damage occurred at the 5.0 m} setting but not at l.2 m} (Table 2). Figure 5 shows a line of hits in an injection-molded IOL corresponding to the area of 5.0 m} treatment. Figure 6 shows a small crack more anterior in the same IOL. Figures 7 and 8 show lathe-cut IOLs from two
Fig. 4. Fig. 3.
(Smith) Refractile particles within IOL in human eye.
J CATARACT REFRACT
(Smith) Test chamber in micrometer-controlled testing device mounted on laser.
(Smith) Pretreatment photograph of refractile particles in test IOL in air. This IOL was rated + + .
SURG-VOL 14, NOVEMBER 1988
661
Table 1. Grading of the IOLs for refractile particles and results of laser treatments. Intraocular Number of Optical Breakdown Within IOL Lens Type Refractile Particles Mode-Locked Q-switched IM* 1M LCt LC LC LC
++ ++ ++ +++ ++ +
0
+++ ++ ++ ++ 0
0 0
IM* LCt
0
LC
0
LC
0
LC
0
DISCUSSION In this study, IOLs were examined for the presence of refractile bodies and then affixed in a test chamber. A YAG laser was focused to a point 2 mm posterior to the IOLs and fired. Optical breakdown occurred within some of the IOLs anterior to the spot where the laser was focused. Since all IOLs had refractile particles, the optical breakdown appeared to be directly related to use of the mode-locked laser rather than the presence of refractile particles. It occurred at high energy levels (5 m}) rather than at low energy levels (1 m}). Damage occurred in both injection-molded and lathe-cut lenses. If the premature breakdown had been caused by laser energy hitting the refractile particles, we would expect to have seen damage with both the Q-switched and mode-locked lasers. This was not the case. Further-
(Smith) Injection-molded IOL with line of optical breakdown pits in area where mode-locked laser, set at 5 mJ, was focused.
J CATARACT REFRACT
++ ++ ++ +++ ++ +
Mode-Locked Laser Setting 1.2 mJ
5.0 mJ
0
0
0
0
+++ ++ ++ ++
0
0
0 0
*IM = injection molded tLC = lathe cut
manufacturers with lines of hits corresponding to the area of 5.0 mJ treatment.
662
Intraocular Number of Lens Type Refractile Particles
1M
*IM = injection molded tLC = lathe cut
Fig ..5.
Table 2. Results of mode-locked laser treatments.
more, if the refractile particles had been a factor for only the mode-locked laser, we would expect to have seen a gradation of injury, with more hits occurring in the IOLs with more refractile particles. This did not occur in the series ofIOLs tested, although the number of IOLs was not large. Two IOLs that had refractile particles were not injured by the mode-locked laser. It is possible that no energy encountered a refractile particle on passing through the IOLs, although one of these lenses was graded + + and others with this rating suffered injury. Another possibility is that the manufacturing technique would prevent injury, as noted by Bath for castmolded IOLs (P. E. Bath, M.D., ''YAG Laser Damage Threshold for Intraocular Lenses," American-International IOL Congress, Boston, April 1985). One lens with no injury was a lathe-cut IOL and one was an injection-molded IOL. Another possibility is that there was a variation in performance of the mode-locked laser.
Fig. 6.
(Smith) Injection-molded lens, as in Figure .5, with crack located in the anterior portion of the optic (arrow).
SC'RG-VOL 14, NOVEMBER 1988
Fig. 7.
(Smith) Lathe-cut lens with line of optic breakdown pits corresponding to area where mode-locked laser set at 5 m] was focused.
The mode-locked laser was clearly a factor in optical breakdown within the IOL in this study. Loertscher2 has noted that the mode-locked laser is more susceptible to self-focusing than the Q-switched laser. In this phenomenon, breakdown occurs anterior to the focus point at powers in excess of a critical value. The convergence angle and the freshness of the dye may also be factors in the laser's function. Other surgeons have noted a variability in the performance of Q-switched lasers between maintenance intervals (Richard L. Lindstrom, M.D., personal communication ; Daniel Kane, M.D., personal communication). The refractile particles were present in all IOLs examined (injection-molded and lathe-cut). This result is similar to Bath's and contrary to Ballin's observations. The refractile particles are not significant in the resolution of the IOLs in human vision, and it does not appear that they are of significance in causing premature optical breakdown with the use of the modelocked laser in this preliminary study. Further work is necessary to confirm this.
J CATARACT REFRACT
Fig. 8.
(Smith) Lathe-cut lens by another manufacturer showing damage similar to that in Figure 7.
This study demonstrated that anterior or premature optical breakdown with the YAG laser can occur frequently, particularly at high energy levels. This was unrelated to surgeon error. The study also demonstrated that with currently manufactured IOLs, some YAG lasers can pass through the IOL without damage. Should a surgeon note the occurrence of optical breakdown anterior to the focus plane after eliminating other variables (patient movement, difficulty in determining the focus plane), we recommend that he or she stop the procedure and have the laser serviced or try a different YAG laser. A needle capsulotomy could also be considered. REFERENCES 1. Bath PE, Fridge DL, Robinson K, McCord RC: Photometric evaluation ofYAG-induced polymethylmethacrylate damage in a keratoprosthesis. A1Il Intra-Ocular Implant Soc] 11:253-256 , 1985 2. Loertscher H: Laser-induced breakdown for ophthalmic applications. In: Trokel SL, ed, lAC Laser Ophthalmic MicroslIrgery. Norwalk, CT, Appleton-Century-Crofts , 1983, pp 39-66
SURG-VOL 14, NOVEMBER 1988
663
B TR T Intraocular I n e s (I OL ') 'uitable for implantation ~ ere anal zed for the pre ence of refractil parti I . The e, ere found in lathe-cut and injection-molded len e from ariou manufacturers. A YAG la er wa foeu ed 2 mm bond the IOL in a p cial te t chamber and fired throu h th m. The IOL were then anal zed for damage. A photographicall documented ·tud of i IOL u ing Q-S\ itched and mode-locked la er how d optical breakdown occurring within the IOL . this \ a not cI arl r lated to J'efractile particle . Optical breakdo\ n did not occur in t\ 0 IOL ,ith a imiJar number of refractile particl . Dama e wa 'een \ ith the mode-locked but n t \ ith the Q- witch d la r. Th optical breakdown occurred more frequ ntl at high pow r (5.0 mJ) than at 10\ power (1.2 mJ).
Ke Word ,: intra cular I n spitting , mod lo·k d l a ' r,Q- 'witch d la ' r r fractil partie1 .
Refractile particles within intraocular lenses (IOLs) were initially noted by Pearce (personal communication) as well as by Ballin (Ocular Surgery News, October 15, 1985, page 14) and Bath.I Pearce and Ballin noted the particles in injection-molded lenses but saw few in lenses manufactured by other techniques. Bath noted particles in all IOL types. One author (SGS) noted a case in which optical breakdown by YAG laser energy occurred within the anterior portion of the IOL optic when the laser appeared to be focused on a point within the vitreous. This observation raised several questions. Was this a correct observation or was it surgeon error? Was it related to the refractile particles? Was it related to the YAG laser? Was it related to the manufacturing technique of the IOL? Was it caused by some other etiology? This study was designed to answer these questions.
MATERIALS AND METHODS Six IOLs that had been approved for implantation were taken from the hospital shelf and examined at the slitlamp and graded for refractile particles. A refractile particle was defined as an area of optical distortion within the IOL optic. On slitlamp examination, refractile particles are seen in oblique illumination and are not visible when a red reflex is present. The majority appear white although some may be red. They may vary in size but are quite small, as seen in Figure 1. After the slitlamp examination, each IOL was placed in a specially constructed test chamber (Figure 2). This chamber had a flat glass anterior surface, an anterior chamber, a micrometer-controlled IOL-holding device that adjusted in an anterior-posterior direction, and a posterior cham ber. This device was affixed to the laser's chin rest, and the entire test chamber containing the
From the General Ophthalmology Service, Wills Eye Hospital, Philadelphia. Pennsylvania, the Department of Ophthalmology, Hershey Medical Center, Hershey, Pennsylvania (Dr. Smith); the 3M Vision CarelIOL Department, Health Care Enterprises Division, and Biosciences Laboratory (Dr. Snowden). Supported ill part by all unrestricted grant from 3M Vision Care. Presented in part at the Symposium on Cataract, IOL and Refractive Surgery, Los Angeles, April 1986. The authors have no proprietary interest in any IOL design. Reprillt requests to S. Gregory Smith, M.D., 1700 Shallcross Avellue, Suite 2, Wilmington, Delaware 19806. 660
J CATARACT REFRACT
SURG-VOL 14, NOVEMBER 1988
Fig. 1.
(Smith) Intraocular lens positioned within test chamber.
IOL was moved horizontally by the micrometer (Figure 3). The posterior surface of the IOL was marked with a scratch and placed in the device, which was mounted on a mode-locked laser (Medical Laser, Inc.). The laser was focused on the scratch and the slitlamp was locked. The IOL was then moved 2 mm anterior to the focus point by the micrometer. The laser was fired through the IOL while it was moved horizontally by the second micrometer on the device. Three lines of laser treatment were delivered at power settings of l.2 m} (60 bursts), 5.0 m} (70 bursts), and l.2 m} (75 bursts). The device was then mounted on a Q-switched laser (Coherent) and the same treatment was given to the bottom half ofthe IOL. It was not removed from the device between treatment with each laser. These power settings were fixed on the modelocked laser and were duplicated on the Q-switched
Fig. 2.
laser. The IOLs were then removed from the chamber, examined for pits, and photographed. RESULTS Photography of the refractile particles was difficult both in vivo and in vitro. Figure 1 demonstrates refractile particles within a human eye. This was graded as + + +. Figure 4 demonstrates refractile particles in an injection-molded lens graded as + + . Table 1 shows the grading of the IOLs and the results of the laser treatments. It reveals that the Q-switched laser did not cause IOL damage. With the mode-locked laser, damage occurred at the 5.0 m} setting but not at l.2 m} (Table 2). Figure 5 shows a line of hits in an injection-molded IOL corresponding to the area of 5.0 m} treatment. Figure 6 shows a small crack more anterior in the same IOL. Figures 7 and 8 show lathe-cut IOLs from two
Fig. 4. Fig. 3.
(Smith) Refractile particles within IOL in human eye.
J CATARACT REFRACT
(Smith) Test chamber in micrometer-controlled testing device mounted on laser.
(Smith) Pretreatment photograph of refractile particles in test IOL in air. This IOL was rated + + .
SURG-VOL 14, NOVEMBER 1988
661
Table 1. Grading of the IOLs for refractile particles and results of laser treatments. Intraocular Number of Optical Breakdown Within IOL Lens Type Refractile Particles Mode-Locked Q-switched IM* 1M LCt LC LC LC
++ ++ ++ +++ ++ +
0
+++ ++ ++ ++ 0
0 0
IM* LCt
0
LC
0
LC
0
LC
0
DISCUSSION In this study, IOLs were examined for the presence of refractile bodies and then affixed in a test chamber. A YAG laser was focused to a point 2 mm posterior to the IOLs and fired. Optical breakdown occurred within some of the IOLs anterior to the spot where the laser was focused. Since all IOLs had refractile particles, the optical breakdown appeared to be directly related to use of the mode-locked laser rather than the presence of refractile particles. It occurred at high energy levels (5 m}) rather than at low energy levels (1 m}). Damage occurred in both injection-molded and lathe-cut lenses. If the premature breakdown had been caused by laser energy hitting the refractile particles, we would expect to have seen damage with both the Q-switched and mode-locked lasers. This was not the case. Further-
(Smith) Injection-molded IOL with line of optical breakdown pits in area where mode-locked laser, set at 5 mJ, was focused.
J CATARACT REFRACT
++ ++ ++ +++ ++ +
Mode-Locked Laser Setting 1.2 mJ
5.0 mJ
0
0
0
0
+++ ++ ++ ++
0
0
0 0
*IM = injection molded tLC = lathe cut
manufacturers with lines of hits corresponding to the area of 5.0 mJ treatment.
662
Intraocular Number of Lens Type Refractile Particles
1M
*IM = injection molded tLC = lathe cut
Fig ..5.
Table 2. Results of mode-locked laser treatments.
more, if the refractile particles had been a factor for only the mode-locked laser, we would expect to have seen a gradation of injury, with more hits occurring in the IOLs with more refractile particles. This did not occur in the series ofIOLs tested, although the number of IOLs was not large. Two IOLs that had refractile particles were not injured by the mode-locked laser. It is possible that no energy encountered a refractile particle on passing through the IOLs, although one of these lenses was graded + + and others with this rating suffered injury. Another possibility is that the manufacturing technique would prevent injury, as noted by Bath for castmolded IOLs (P. E. Bath, M.D., ''YAG Laser Damage Threshold for Intraocular Lenses," American-International IOL Congress, Boston, April 1985). One lens with no injury was a lathe-cut IOL and one was an injection-molded IOL. Another possibility is that there was a variation in performance of the mode-locked laser.
Fig. 6.
(Smith) Injection-molded lens, as in Figure .5, with crack located in the anterior portion of the optic (arrow).
SC'RG-VOL 14, NOVEMBER 1988
Fig. 7.
(Smith) Lathe-cut lens with line of optic breakdown pits corresponding to area where mode-locked laser set at 5 m] was focused.
The mode-locked laser was clearly a factor in optical breakdown within the IOL in this study. Loertscher2 has noted that the mode-locked laser is more susceptible to self-focusing than the Q-switched laser. In this phenomenon, breakdown occurs anterior to the focus point at powers in excess of a critical value. The convergence angle and the freshness of the dye may also be factors in the laser's function. Other surgeons have noted a variability in the performance of Q-switched lasers between maintenance intervals (Richard L. Lindstrom, M.D., personal communication ; Daniel Kane, M.D., personal communication). The refractile particles were present in all IOLs examined (injection-molded and lathe-cut). This result is similar to Bath's and contrary to Ballin's observations. The refractile particles are not significant in the resolution of the IOLs in human vision, and it does not appear that they are of significance in causing premature optical breakdown with the use of the modelocked laser in this preliminary study. Further work is necessary to confirm this.
J CATARACT REFRACT
Fig. 8.
(Smith) Lathe-cut lens by another manufacturer showing damage similar to that in Figure 7.
This study demonstrated that anterior or premature optical breakdown with the YAG laser can occur frequently, particularly at high energy levels. This was unrelated to surgeon error. The study also demonstrated that with currently manufactured IOLs, some YAG lasers can pass through the IOL without damage. Should a surgeon note the occurrence of optical breakdown anterior to the focus plane after eliminating other variables (patient movement, difficulty in determining the focus plane), we recommend that he or she stop the procedure and have the laser serviced or try a different YAG laser. A needle capsulotomy could also be considered. REFERENCES 1. Bath PE, Fridge DL, Robinson K, McCord RC: Photometric evaluation ofYAG-induced polymethylmethacrylate damage in a keratoprosthesis. A1Il Intra-Ocular Implant Soc] 11:253-256 , 1985 2. Loertscher H: Laser-induced breakdown for ophthalmic applications. In: Trokel SL, ed, lAC Laser Ophthalmic MicroslIrgery. Norwalk, CT, Appleton-Century-Crofts , 1983, pp 39-66
SURG-VOL 14, NOVEMBER 1988
663