- Email: [email protected]
Anterior capsulotomy with an ultrashort-pulse laser
ARTICLE
Anterior capsulotomy with an ultrashort-pulse laser Ramon Naranjo Tackman, MD, Jorge Villar Kuri, MD†, Louis D. (Skip) Nichamin, MD, Keith Edwards, FCOptom
PURPOSE: To assess the precision of laser anterior capsulotomy compared with that of manual continuous curvilinear capsulorhexis (CCC). SETTING: Asociaci on Para Evitar La Ceguera en Mexico IAP, Hospital Dr. Luis Sanchez Bulnes, Mexico City, Mexico. DESIGN: Nonrandomized single-center clinical trial. METHODS: In patients presenting for cataract surgery, the LensAR Laser System was used to create a laser anterior capsulotomy of the surgeon’s desired size. Capsule buttons were retrieved and measured and then compared with buttons retrieved from eyes having a manually torn CCC. Deviation from the intended diameter and the regularity of shape were assessed. When removing the capsule buttons at the start of surgery, the surgeon rated the ease of removal on a scale of 1 to 10 (1 Z required manual capsulorhexis around the whole diameter; 10 Z button free floating or required no manual detachment from remaining capsule during removal). RESULTS: The mean deviation from the intended diameter was 0.16 mm G 0.17 (SD) for laser anterior capsulotomy and 0.42 G 0.54 mm for CCC (PZ.03). The mean absolute deviation from the intended diameter was 0.20 G 0.12 mm and 0.49 G 0.47 mm, respectively (PZ.003). The mean of the average squared residuals was 0.01 G 0.03 and 0.02 G 0.04, respectively (PZ.09). The median rating of the ease of removal was 9 (range 5 to 10). CONCLUSIONS: Laser anterior capsulotomy created a more precise capsule opening than CCC, and the buttons created by the laser procedure were easy to remove at the beginning of cataract surgery. Financial Disclosure: Financial disclosures are found in the footnotes. J Cataract Refract Surg 2011; 37:819–824 Q 2011 ASCRS and ESCRS
Anterior capsulotomy or capsulorhexis is the primary step in cataract surgery that can influence the position and centration of implanted intraocular lenses (IOLs),1 especially premium IOLs.2 The size, shape, and centration of the capsulorhexis can be variable depending on the type of cataract3–5 as well as the surgeon’s experience. Several options have been assessed as an alternative to conventional manual continuous curvilinear capsulorhexis (CCC). The Fugo blade has been used to create anterior capsulotomies using a plasma technique. In a study by Izak et al.,6 the edge of the capsulotomy was more irregular but was not more prone to the formation of radial tears because of the geometry of the remaining tags. High-frequency diathermy has also been applied to anterior capsulotomy.7–9 There is some question about capsule integrity with this technique because cautery can cause some irregularity Q 2011 ASCRS and ESCRS Published by Elsevier Inc.
and weakening at the capsule margin,10 potentially giving rise to anterior radial tears.11 Several studies12–14 have assessed the use of neodymium:YAG and erbium:YAG lasers for anterior capsulotomy, with results suggesting the laser is a more precise and faster method than CCC. Some authors suggest that the technique avoids radial tears15 and provides a useful alternative in intumescent cataract, in which the risk for uncontrolled extension of the manual opening is always present.3–5 Lin and Li16 found improved outcomes with Nd:YAG laser capsulotomy in congenital cataract as well as easier lens aspiration. When assessing the edge of the cut capsulotomy, Radner et al.10 found the erbium:YAG capsulotomy edge to be intermediate between CCC and high-frequency diathermy in signs of denaturation, mechanical disruption, tears, and microtears. Lens capsule edges with CCC were smooth with no irregularities. 0886-3350/$ - see front matter doi:10.1016/j.jcrs.2010.11.030
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More recently, dedicated ultrashort-pulse lasers have been applied to laser cataract surgery. ReportsA–D provide early results from 3 developmental lasers being used in feasibility and regulatory studies. Nagy et al.17 found in animal studies that laser anterior capsulotomy was more accurate than manual CCC in obtaining the desired capsulotomy diameter. This current study evaluated the results of laser anterior capsulotomy in a clinical cohort of patients in which the retained capsule button was measured using proprietary image-analysis software. PATIENTS AND METHODS Eligible patients electing to have routine cataract surgery were recruited to this study after signing an informed consent document approved by an institutional review board. The study was approved by Cofepris, the Mexican regulatory authority, and is registered on clinicaltrials.gov with ID NCT01001117. In this nonrandomized nonmasked study, the first eye was treated with the LensAR Laser System (LensAR, Inc), with surgeries performed in a hospital outpatient surgery center. Immediately before cataract surgery, an anterior capsulotomy was created using the laser system at the diameter preferred by the surgeon. In cases in which the pupil did not dilate to a diameter larger than this, the largest capsulotomy diameter that would fit safely within the pupil area was selected. After appropriate anesthesia was administered, the patient was docked to the laser via a low-pressure suction ring and index-matching device that did not applanate the cornea. The anterior eye was
Submitted: September 30, 2010. Final revision submitted: November 12, 2010. Accepted: November 12, 2010. From Corneal and Refractive Surgery (Tackman), National University of Mexico and Panamerican University School of Medicine, Asociacion Para Evitar La Ceguera en Mexico IAP (Villar Kuri), Hospital Dr Luis Sanchez Bulnes, Mexico City, Mexico; Laurel Eye Clinic (Nichamin), Brookville, Pennsylvania, and Clinical and Regulatory Affairs (Edwards), LensAR, Inc., Orlando, Florida, USA. †
Deceased.
Additional financial disclosures: Drs. Naranjo Trackman and Villar Kuri are consultants to and principal investigators in LensAR, Inc., and have a nonmonetary interest in the company. Dr. Nichamin is a consultant to and investigator for LensAR, Inc., and has a financial interest in the company. Mr. Edwards is an employee of LensAR, Inc. Funded by LensAR, Inc. Joe Bielitzki helped photograph the buttons. Theodora Bunch performed the LensProfile analysis. Keith Peck performed the statistical analysis. Corresponding author: Keith Edwards, FCOptom, LensAR, Inc., 2800 Discovery Dive. Orlando, Florida 32826, USA. E-mail: keith. [email protected].
Figure 1. Image of a stained capsulotomy button with the edge marked using the proprietary software.
then imaged using the proprietary imaging and analysis software, after which the size and position of the capsulotomy were programmed. The surgeon could modify the instrument-determined centration of the capsulotomy over the pupil. The laser was then used to cut the capsulotomy, after which the patient was undocked and went on to routine cataract surgery. After routine prepping and draping of the patient, the surgeon made his normal incisions and introduced an ophthalmic viscosurgical device. The cut capsule button was detached from the remaining capsule; the surgeon scored the ease of removal on a scale of 1 to 10, on which 1 was a largely uncut capsulotomy that required a full manual capsulorhexis and 10 was a free-floating button or a button that required no manual detachment from the remaining capsule. The buttons were retained and stored in a balanced salt solution until they could be measured. As a control group, the buttons from patients having CCC were retained and measured using the same software. Analysis was made by lightly staining the buttons to enhance visibility and then opening and laying them flat on a microscope stage before photographing them with a digital camera. The resulting images were analyzed using proprietary LensProfile software. A single operator placed marks along the edge of the image of the button, being careful to clearly delineate irregularities. The software then computed 1000 points to fit within the marks placed on the image. A best-fit circle was calculated and applied to the image; the circle represented the best assessment of achieved diameter. This was compared with the target diameter. As an assessment of regularity of shape, the software ran an analysis of residuals of the difference between the actual button and the best-fit circle. These analyses were also applied to the manually torn CCCs. Figure 1 shows the placement of marks on the button. Figure 2 shows the calculated best-fit circle and diameter as well as the estimated residuals. Figure 3 shows the fit of the targeted 5.0 mm capsulorhexis. The difference between the unconstrained best-fit circle in Figure 2 and the 5.0 mm target is the difference in target diameter versus achieved diameter. The residuals of the difference between the best-fit circle shown in blue and the actual button edge marked in red are shown in the right-hand section of the window along with the average deviation. To calculate regularity of shape, the residuals between the button and the unconstrained bestfit circle were used.
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Figure 2. The best-fit circle of diameter 4.92 mm shown in blue with the capsulotomy button edge indicated in red computed from 1000 points around the circumference. The right-hand black panel shows maximum and average deviation from the best-fit circle and the residuals.
In evaluating the significance of results, differences between attempted and achieved capsulotomy were assessed using a 2-tailed 2-sample t test, assuming unequal variances. In assessing the regularity of the capsulotomies, a 2-sample F-test for variances was performed on the average squared residual values.
RESULTS Of the 53 buttons collected in the laser anterior capsulotomy group, 4 were rejected as being incomplete,
making image analysis impossible. Of the 28 buttons collected in the CCC group, 4 were rejected as being incomplete, making image analysis impossible. Table 1 shows the capsulotomy data in the 2 groups. The difference in attempted versus achieved diameter was statistically significantly smaller in the laser anterior capsulotomy group than in the CCC group (PZ.03). The mean absolute value of the attempted versus achieved diameter was 0.20 G 0.12 mm in the laser anterior capsulotomy group and 0.49 G 0.47 mm in
Figure 3. The same image as Figure 2 but with the best-fit circle constrained to the intended 5.00 mm diameter.
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Table 1. Capsulotomy data by group. Diameter (mm) Group Laser (n Z 49) Mean SD CCC (n Z 24) Mean SD
Attempted
Measured
5.23 0.06
5.08 0.18
5.36 0.55
4.95 0.53
Mean Squared Residual to Best-Fit Circle (mm2)
RMS of Residuals to Best-Fit Circle (mm)
0.16 0.17
0.0105 d
0.10 d
0.42 0.54
0.0243 d
0.16 d
Attempted
Achieved
CCC Z continuous curvilinear capsulorhexis
the CCC group. The difference between the 2 groups was statistically significant (PZ.003). The mean of the average of the squared residuals to the best-fit circle was 0.01 G 0.03 mm2 in the laser anterior capsulotomy group and 0.02 G 0.04 mm2 in the CCC group. Although the value in the CCC group was numerically higher by a factor of 2, the difference reached statistical significance only at the 90% level (PZ.09). Figure 4 shows the surgeon’s assessment of the ease of removal. The median score for ease of removal was 9 (range 5 to 10). Nearly half the cases were rated with an ease of removal score of 10, which required no manipulation to separate the button from the remaining capsule. Overall, 96% of cases were scored at 7 or better, suggesting that little manual manipulation was required. DISCUSSION Given the importance of creating a well-centered and symmetrically shaped anterior capsule opening, it is not surprising that alternatives to CCC have been
Figure 4. Surgeon assessment of ease of opening in the laser anterior capsulotomy patients on a scale of 1 to 10 (1 Z required manual capsulorhexis around the whole diameter; 10 Z button free floating or required no manual detachment from remaining capsule during removal).
investigated.1 Any device that can create a more precise and repeatable capsulotomy will help both experienced and less experienced surgeons produce a more consistent outcome even in the most difficult cases, such as intumescent cataract in which the capsule may be more prone to tearing.3–5 For maximum benefit, application of the capsulotomy cut should be made with an immobilized eye. To this end, a system that docks the eye to a laser via a suction ring would seem to provide the most stable setting for locating and measuring the ocular structures and then applying the treatment to the eye without risking movement. Manual application of plasma blades or diathermy is less precise than a docking system for diameter and centration. The data presented here, although from early clinical feasibility assessments, show the benefit of laser anterior capsulotomy in providing a capsulotomy of the intended diameter compared with a manual method. In the latter, capsulotomy size is largely a matter of judgment and the position and shape are a function of the prevailing conditions, such as degree of pupil dilation, position of the Purkinje images, and the grade of cataract, all of which can influence the ease with which the CCC can be torn. It would also be expected that the regularity of shape would be better with laser anterior capsulotomy than with CCC; however, our data did not support a statistically significant difference in this assessment. This may reflect the experience of the cataract surgeon in creating a CCC but may also be partially explained by the conservative approach taken to the inclusion of samples for the measurement assessment. It is not uncommon for the CCC button to be retrieved in pieces, and it was not always possible to reconstruct the complete button. If the photograph did not clearly indicate the overall shape and size of the button without undue extrapolation in the placement of the software markers, the button was excluded. This tended to exclude the worst of the CCC samples and retain the more regular and complete buttons. In contrast, even
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Figure 5. Examples of retrieved CCC buttons that were excluded from analysis.
the excluded laser anterior capsulotomy buttons looked relatively regular in shape but still had too many gaps to allow accurate assessment. Figure 5 shows examples of incomplete CCC buttons that were excluded from analysis. Figure 6 shows a laser anterior capsulotomy button in which the laser cut was of inadequate depth in 1 area and the resulting manual tear led to an irregular mouse-ear shape. The
Figure 6. Example of laser anterior capsulotomy button with significant irregularity due to inadequate cut in 1 area, leading to a mouseear effect on manual separation. The true line of scoring of the inadequate laser cut can be seen as part of the main button.
actual laser cut can be seen to complete an almost perfect circle. This single case led to a significant increase in residuals in the laser group, which affected the comparison with CCC cases. In more recent cases in which a refined system was used, there were no cases of this type of partial capsulotomy cut. The surgeon evaluation of ease of opening found that the laser anterior capsulotomy button was easily removed at the beginning of surgery. The assessments were completed during an early feasibility stage of the laser development; in the last series of cases with the same laser at the same site, 86% of cases were rated with a score of 10 and 14% with a score of 9, suggesting that the refined system provides more consistently good results. Laser anterior capsulotomy provides a more precise capsulotomy than manual methods, being significantly closer to the intended diameter than CCC with less variance in outcome. Further studies should be performed to determine whether there is significant improvement in the regularity of shape compared with that of manual methods. The capsule buttons were easy to remove at the beginning of surgery. Improved predictability of capsulotomy size and centration should improve outcomes by ensuring good IOL centration and position. This is particularly important for accommodating,2 multifocal,18 toric, and aspheric19 IOLs.
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Although both shape and positioning of capsule openings are critical in modern cataract surgery, so is the stability of the capsule opening. Histology and biomechanical investigations will be of interest in assessing this aspect of laser cataract surgery. REFERENCES 1. Chang DF. Strategies for difficult capsulorrhexis. In: Chang DF, ed, Phaco Chop; Mastering Techniques, Optimizing Technology and Avoiding Complications. Thorofare, NJ, Slack, 2004; 143–161 2. Davies JA. Cristalens 4.5 versus 5.0dwhat is the difference? In: Chang DF, ed, Mastering Refractive IOLs; the Art and Science. Thorofare, NJ, Slack, 2008; 179–181 3. Coelho RP, Martin LFT, Paula JS, Scott IU. Comparison of preoperative Nd:YAG laser anterior capsulotomy versus two-stage curvilinear capsulorhexis in phacoemulsification of white intumescent cataracts. Ophthalmic Surg Lasers Imaging 2009; 40:582–585 4. Coelho RP, Paula JS, Silva RN, Garcia TV, Martin LFT. Preoperative Nd:YAG laser anterior capsulotomy in white intumescent cataracts: report of 11 cases. Arq Bras Oftalmol 2009; 72: 113–115. Available at: http://www.scielo.br/pdf/abo/v72n1/ v72n1a24.pdf. Accessed December 21, 2010 5. Richards JC, Harrison DC. Preoperative neodymium:YAG anterior capsulotomy in intumescent cataract: preventing extension of the capsular tear to the lens periphery. J Cataract Refract Surg 2003; 29:1630–1631 6. Izak AM, Werner L, Pandey SK, Apple DJ, Izak MGJ. Analysis of the capsule edge after Fugo plasma blade capsulotomy, continuous curvilinear capsulorhexis, and can-opener capsulotomy. J Cataract Refract Surg 2004; 30:2606–2611 7. Delcoigne CD, Hennekes R. Circular continuous anterior capsulotomy with high frequency diathermy. Bull Soc Belge Ophtalmol 1993; 249:67–72 €ti R. Anterior capsulotomy 8. Gassmann F, Schimmelpfennig B, Klo by means of bipolar radio-frequency endodiathermy. J Cataract Refract Surg 1988; 14:673–676 €ti R. Vordere Hochfrequenz(HF)-Kapsulotomie. I. Experi9. Klo mentelle Studie [Anterior high frequency capsulotomy. I. Experimental study]. Klin Monbl Augenheilkd 1992; 200:507–510 10. Radner G, Amon M, Stifter E, Nepp J, Diendorfer G, Mallinger R, Radner W. Tissue damage at anterior capsule edges after continuous curvilinear capsulorhexis, high-frequency capsulotomy, and erbium:YAG laser capsulotomy. J Cataract Refract Surg 2004; 30:67–73 11. Aron-Rosa DS, Aron JJ. Effect of preoperative YAG laser anterior capsulotomy on the incidence of posterior capsule opacification: ten year follow-up. J Cataract Refract Surg 1992; 18: 559–561
12. Panda A, Pattnaik NK. Neodymium:yttrium aluminum garnet laser anterior capsulotomy. Ann Ophthalmol 1991; 23:334–336 13. Chambless WS. Neodymium:YAG laser anterior capsulotomy and a possible new application. Am Intra-Ocular Implant Soc J 1985; 11:33–34 14. Richburg FA. Neodymium: YAG laser for anterior capsulotomy. Am Intra-ocular Implant Soc J 1985; 11:372–375 15. O’Donnell FE Jr. YAG anterior capsulotomy avoids anterior radial tears [letter]. J Cataract Refract Surg 1989; 15: 600–601 16. Lin Z, Li S. Comparison of the effectiveness between anterior capsulotomy with Nd:YAG laser and with bent needle in patients with congenital cataract. Yan Ke Xue Bao 1991; 7: 125–127; 124 17. Nagy Z, Takacs A, Filkorn T, Sarayba M. Initial clinical evaluation of an intraocular femtosecond laser in cataract surgery. J Refract Surg 2009; 25:1053–1060 18. Hayashi K, Hayashi H, Nakao F, Hayashi F. Correlation between pupillary size and intraocular lens decentration and visual acuity of a zonal-progressive multifocal lens and a monofocal lens. Ophthalmology 2001; 108:2011–2017 19. Altmann GE, Nichamin LD, Lane SS, Pepose JS. Optical performance of 3 intraocular lens designs in the presence of decentration. J Cataract Refract Surg 2005; 31:574–585
OTHER CITED MATERIAL A. Talamo JH, “Refractive Cataract Surgery with a Femtolaser,” presented at the annual meeting of the American Academy of Ophthalmology, San Francisco, California, USA, October 2009 B. Nagy Z, “One-Year Clinical Experience With a New Femtosecond Laser for Refractive Cataract Surgery,” presented at the annual meeting of the American Academy of Ophthalmology, San Francisco, California, USA, October 2009 C. Nichamin LD, “Laser Capsulotomy With the LensAR Laser System (LLS),” presented at the annual meeting of the American Academy of Ophthalmology, San Francisco, California, USA, October 2009 D. Naranjo-Tackman R, “Novel Uses of a Femtosecond Laser,” presented at the annual meeting of the American Academy of Ophthalmology, San Francisco, California, USA, October 2009
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First author: Ramon Naranjo Tackman, MD Corneal and Refractive Surgery, National University of Mexico and Panamerican University School of Medicine, Mexico City, Mexico
Anterior capsulotomy with an ultrashort-pulse laser Ramon Naranjo Tackman, MD, Jorge Villar Kuri, MD†, Louis D. (Skip) Nichamin, MD, Keith Edwards, FCOptom
PURPOSE: To assess the precision of laser anterior capsulotomy compared with that of manual continuous curvilinear capsulorhexis (CCC). SETTING: Asociaci on Para Evitar La Ceguera en Mexico IAP, Hospital Dr. Luis Sanchez Bulnes, Mexico City, Mexico. DESIGN: Nonrandomized single-center clinical trial. METHODS: In patients presenting for cataract surgery, the LensAR Laser System was used to create a laser anterior capsulotomy of the surgeon’s desired size. Capsule buttons were retrieved and measured and then compared with buttons retrieved from eyes having a manually torn CCC. Deviation from the intended diameter and the regularity of shape were assessed. When removing the capsule buttons at the start of surgery, the surgeon rated the ease of removal on a scale of 1 to 10 (1 Z required manual capsulorhexis around the whole diameter; 10 Z button free floating or required no manual detachment from remaining capsule during removal). RESULTS: The mean deviation from the intended diameter was 0.16 mm G 0.17 (SD) for laser anterior capsulotomy and 0.42 G 0.54 mm for CCC (PZ.03). The mean absolute deviation from the intended diameter was 0.20 G 0.12 mm and 0.49 G 0.47 mm, respectively (PZ.003). The mean of the average squared residuals was 0.01 G 0.03 and 0.02 G 0.04, respectively (PZ.09). The median rating of the ease of removal was 9 (range 5 to 10). CONCLUSIONS: Laser anterior capsulotomy created a more precise capsule opening than CCC, and the buttons created by the laser procedure were easy to remove at the beginning of cataract surgery. Financial Disclosure: Financial disclosures are found in the footnotes. J Cataract Refract Surg 2011; 37:819–824 Q 2011 ASCRS and ESCRS
Anterior capsulotomy or capsulorhexis is the primary step in cataract surgery that can influence the position and centration of implanted intraocular lenses (IOLs),1 especially premium IOLs.2 The size, shape, and centration of the capsulorhexis can be variable depending on the type of cataract3–5 as well as the surgeon’s experience. Several options have been assessed as an alternative to conventional manual continuous curvilinear capsulorhexis (CCC). The Fugo blade has been used to create anterior capsulotomies using a plasma technique. In a study by Izak et al.,6 the edge of the capsulotomy was more irregular but was not more prone to the formation of radial tears because of the geometry of the remaining tags. High-frequency diathermy has also been applied to anterior capsulotomy.7–9 There is some question about capsule integrity with this technique because cautery can cause some irregularity Q 2011 ASCRS and ESCRS Published by Elsevier Inc.
and weakening at the capsule margin,10 potentially giving rise to anterior radial tears.11 Several studies12–14 have assessed the use of neodymium:YAG and erbium:YAG lasers for anterior capsulotomy, with results suggesting the laser is a more precise and faster method than CCC. Some authors suggest that the technique avoids radial tears15 and provides a useful alternative in intumescent cataract, in which the risk for uncontrolled extension of the manual opening is always present.3–5 Lin and Li16 found improved outcomes with Nd:YAG laser capsulotomy in congenital cataract as well as easier lens aspiration. When assessing the edge of the cut capsulotomy, Radner et al.10 found the erbium:YAG capsulotomy edge to be intermediate between CCC and high-frequency diathermy in signs of denaturation, mechanical disruption, tears, and microtears. Lens capsule edges with CCC were smooth with no irregularities. 0886-3350/$ - see front matter doi:10.1016/j.jcrs.2010.11.030
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More recently, dedicated ultrashort-pulse lasers have been applied to laser cataract surgery. ReportsA–D provide early results from 3 developmental lasers being used in feasibility and regulatory studies. Nagy et al.17 found in animal studies that laser anterior capsulotomy was more accurate than manual CCC in obtaining the desired capsulotomy diameter. This current study evaluated the results of laser anterior capsulotomy in a clinical cohort of patients in which the retained capsule button was measured using proprietary image-analysis software. PATIENTS AND METHODS Eligible patients electing to have routine cataract surgery were recruited to this study after signing an informed consent document approved by an institutional review board. The study was approved by Cofepris, the Mexican regulatory authority, and is registered on clinicaltrials.gov with ID NCT01001117. In this nonrandomized nonmasked study, the first eye was treated with the LensAR Laser System (LensAR, Inc), with surgeries performed in a hospital outpatient surgery center. Immediately before cataract surgery, an anterior capsulotomy was created using the laser system at the diameter preferred by the surgeon. In cases in which the pupil did not dilate to a diameter larger than this, the largest capsulotomy diameter that would fit safely within the pupil area was selected. After appropriate anesthesia was administered, the patient was docked to the laser via a low-pressure suction ring and index-matching device that did not applanate the cornea. The anterior eye was
Submitted: September 30, 2010. Final revision submitted: November 12, 2010. Accepted: November 12, 2010. From Corneal and Refractive Surgery (Tackman), National University of Mexico and Panamerican University School of Medicine, Asociacion Para Evitar La Ceguera en Mexico IAP (Villar Kuri), Hospital Dr Luis Sanchez Bulnes, Mexico City, Mexico; Laurel Eye Clinic (Nichamin), Brookville, Pennsylvania, and Clinical and Regulatory Affairs (Edwards), LensAR, Inc., Orlando, Florida, USA. †
Deceased.
Additional financial disclosures: Drs. Naranjo Trackman and Villar Kuri are consultants to and principal investigators in LensAR, Inc., and have a nonmonetary interest in the company. Dr. Nichamin is a consultant to and investigator for LensAR, Inc., and has a financial interest in the company. Mr. Edwards is an employee of LensAR, Inc. Funded by LensAR, Inc. Joe Bielitzki helped photograph the buttons. Theodora Bunch performed the LensProfile analysis. Keith Peck performed the statistical analysis. Corresponding author: Keith Edwards, FCOptom, LensAR, Inc., 2800 Discovery Dive. Orlando, Florida 32826, USA. E-mail: keith. [email protected].
Figure 1. Image of a stained capsulotomy button with the edge marked using the proprietary software.
then imaged using the proprietary imaging and analysis software, after which the size and position of the capsulotomy were programmed. The surgeon could modify the instrument-determined centration of the capsulotomy over the pupil. The laser was then used to cut the capsulotomy, after which the patient was undocked and went on to routine cataract surgery. After routine prepping and draping of the patient, the surgeon made his normal incisions and introduced an ophthalmic viscosurgical device. The cut capsule button was detached from the remaining capsule; the surgeon scored the ease of removal on a scale of 1 to 10, on which 1 was a largely uncut capsulotomy that required a full manual capsulorhexis and 10 was a free-floating button or a button that required no manual detachment from the remaining capsule. The buttons were retained and stored in a balanced salt solution until they could be measured. As a control group, the buttons from patients having CCC were retained and measured using the same software. Analysis was made by lightly staining the buttons to enhance visibility and then opening and laying them flat on a microscope stage before photographing them with a digital camera. The resulting images were analyzed using proprietary LensProfile software. A single operator placed marks along the edge of the image of the button, being careful to clearly delineate irregularities. The software then computed 1000 points to fit within the marks placed on the image. A best-fit circle was calculated and applied to the image; the circle represented the best assessment of achieved diameter. This was compared with the target diameter. As an assessment of regularity of shape, the software ran an analysis of residuals of the difference between the actual button and the best-fit circle. These analyses were also applied to the manually torn CCCs. Figure 1 shows the placement of marks on the button. Figure 2 shows the calculated best-fit circle and diameter as well as the estimated residuals. Figure 3 shows the fit of the targeted 5.0 mm capsulorhexis. The difference between the unconstrained best-fit circle in Figure 2 and the 5.0 mm target is the difference in target diameter versus achieved diameter. The residuals of the difference between the best-fit circle shown in blue and the actual button edge marked in red are shown in the right-hand section of the window along with the average deviation. To calculate regularity of shape, the residuals between the button and the unconstrained bestfit circle were used.
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Figure 2. The best-fit circle of diameter 4.92 mm shown in blue with the capsulotomy button edge indicated in red computed from 1000 points around the circumference. The right-hand black panel shows maximum and average deviation from the best-fit circle and the residuals.
In evaluating the significance of results, differences between attempted and achieved capsulotomy were assessed using a 2-tailed 2-sample t test, assuming unequal variances. In assessing the regularity of the capsulotomies, a 2-sample F-test for variances was performed on the average squared residual values.
RESULTS Of the 53 buttons collected in the laser anterior capsulotomy group, 4 were rejected as being incomplete,
making image analysis impossible. Of the 28 buttons collected in the CCC group, 4 were rejected as being incomplete, making image analysis impossible. Table 1 shows the capsulotomy data in the 2 groups. The difference in attempted versus achieved diameter was statistically significantly smaller in the laser anterior capsulotomy group than in the CCC group (PZ.03). The mean absolute value of the attempted versus achieved diameter was 0.20 G 0.12 mm in the laser anterior capsulotomy group and 0.49 G 0.47 mm in
Figure 3. The same image as Figure 2 but with the best-fit circle constrained to the intended 5.00 mm diameter.
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Table 1. Capsulotomy data by group. Diameter (mm) Group Laser (n Z 49) Mean SD CCC (n Z 24) Mean SD
Attempted
Measured
5.23 0.06
5.08 0.18
5.36 0.55
4.95 0.53
Mean Squared Residual to Best-Fit Circle (mm2)
RMS of Residuals to Best-Fit Circle (mm)
0.16 0.17
0.0105 d
0.10 d
0.42 0.54
0.0243 d
0.16 d
Attempted
Achieved
CCC Z continuous curvilinear capsulorhexis
the CCC group. The difference between the 2 groups was statistically significant (PZ.003). The mean of the average of the squared residuals to the best-fit circle was 0.01 G 0.03 mm2 in the laser anterior capsulotomy group and 0.02 G 0.04 mm2 in the CCC group. Although the value in the CCC group was numerically higher by a factor of 2, the difference reached statistical significance only at the 90% level (PZ.09). Figure 4 shows the surgeon’s assessment of the ease of removal. The median score for ease of removal was 9 (range 5 to 10). Nearly half the cases were rated with an ease of removal score of 10, which required no manipulation to separate the button from the remaining capsule. Overall, 96% of cases were scored at 7 or better, suggesting that little manual manipulation was required. DISCUSSION Given the importance of creating a well-centered and symmetrically shaped anterior capsule opening, it is not surprising that alternatives to CCC have been
Figure 4. Surgeon assessment of ease of opening in the laser anterior capsulotomy patients on a scale of 1 to 10 (1 Z required manual capsulorhexis around the whole diameter; 10 Z button free floating or required no manual detachment from remaining capsule during removal).
investigated.1 Any device that can create a more precise and repeatable capsulotomy will help both experienced and less experienced surgeons produce a more consistent outcome even in the most difficult cases, such as intumescent cataract in which the capsule may be more prone to tearing.3–5 For maximum benefit, application of the capsulotomy cut should be made with an immobilized eye. To this end, a system that docks the eye to a laser via a suction ring would seem to provide the most stable setting for locating and measuring the ocular structures and then applying the treatment to the eye without risking movement. Manual application of plasma blades or diathermy is less precise than a docking system for diameter and centration. The data presented here, although from early clinical feasibility assessments, show the benefit of laser anterior capsulotomy in providing a capsulotomy of the intended diameter compared with a manual method. In the latter, capsulotomy size is largely a matter of judgment and the position and shape are a function of the prevailing conditions, such as degree of pupil dilation, position of the Purkinje images, and the grade of cataract, all of which can influence the ease with which the CCC can be torn. It would also be expected that the regularity of shape would be better with laser anterior capsulotomy than with CCC; however, our data did not support a statistically significant difference in this assessment. This may reflect the experience of the cataract surgeon in creating a CCC but may also be partially explained by the conservative approach taken to the inclusion of samples for the measurement assessment. It is not uncommon for the CCC button to be retrieved in pieces, and it was not always possible to reconstruct the complete button. If the photograph did not clearly indicate the overall shape and size of the button without undue extrapolation in the placement of the software markers, the button was excluded. This tended to exclude the worst of the CCC samples and retain the more regular and complete buttons. In contrast, even
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Figure 5. Examples of retrieved CCC buttons that were excluded from analysis.
the excluded laser anterior capsulotomy buttons looked relatively regular in shape but still had too many gaps to allow accurate assessment. Figure 5 shows examples of incomplete CCC buttons that were excluded from analysis. Figure 6 shows a laser anterior capsulotomy button in which the laser cut was of inadequate depth in 1 area and the resulting manual tear led to an irregular mouse-ear shape. The
Figure 6. Example of laser anterior capsulotomy button with significant irregularity due to inadequate cut in 1 area, leading to a mouseear effect on manual separation. The true line of scoring of the inadequate laser cut can be seen as part of the main button.
actual laser cut can be seen to complete an almost perfect circle. This single case led to a significant increase in residuals in the laser group, which affected the comparison with CCC cases. In more recent cases in which a refined system was used, there were no cases of this type of partial capsulotomy cut. The surgeon evaluation of ease of opening found that the laser anterior capsulotomy button was easily removed at the beginning of surgery. The assessments were completed during an early feasibility stage of the laser development; in the last series of cases with the same laser at the same site, 86% of cases were rated with a score of 10 and 14% with a score of 9, suggesting that the refined system provides more consistently good results. Laser anterior capsulotomy provides a more precise capsulotomy than manual methods, being significantly closer to the intended diameter than CCC with less variance in outcome. Further studies should be performed to determine whether there is significant improvement in the regularity of shape compared with that of manual methods. The capsule buttons were easy to remove at the beginning of surgery. Improved predictability of capsulotomy size and centration should improve outcomes by ensuring good IOL centration and position. This is particularly important for accommodating,2 multifocal,18 toric, and aspheric19 IOLs.
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Although both shape and positioning of capsule openings are critical in modern cataract surgery, so is the stability of the capsule opening. Histology and biomechanical investigations will be of interest in assessing this aspect of laser cataract surgery. REFERENCES 1. Chang DF. Strategies for difficult capsulorrhexis. In: Chang DF, ed, Phaco Chop; Mastering Techniques, Optimizing Technology and Avoiding Complications. Thorofare, NJ, Slack, 2004; 143–161 2. Davies JA. Cristalens 4.5 versus 5.0dwhat is the difference? In: Chang DF, ed, Mastering Refractive IOLs; the Art and Science. Thorofare, NJ, Slack, 2008; 179–181 3. Coelho RP, Martin LFT, Paula JS, Scott IU. Comparison of preoperative Nd:YAG laser anterior capsulotomy versus two-stage curvilinear capsulorhexis in phacoemulsification of white intumescent cataracts. Ophthalmic Surg Lasers Imaging 2009; 40:582–585 4. Coelho RP, Paula JS, Silva RN, Garcia TV, Martin LFT. Preoperative Nd:YAG laser anterior capsulotomy in white intumescent cataracts: report of 11 cases. Arq Bras Oftalmol 2009; 72: 113–115. Available at: http://www.scielo.br/pdf/abo/v72n1/ v72n1a24.pdf. Accessed December 21, 2010 5. Richards JC, Harrison DC. Preoperative neodymium:YAG anterior capsulotomy in intumescent cataract: preventing extension of the capsular tear to the lens periphery. J Cataract Refract Surg 2003; 29:1630–1631 6. Izak AM, Werner L, Pandey SK, Apple DJ, Izak MGJ. Analysis of the capsule edge after Fugo plasma blade capsulotomy, continuous curvilinear capsulorhexis, and can-opener capsulotomy. J Cataract Refract Surg 2004; 30:2606–2611 7. Delcoigne CD, Hennekes R. Circular continuous anterior capsulotomy with high frequency diathermy. Bull Soc Belge Ophtalmol 1993; 249:67–72 €ti R. Anterior capsulotomy 8. Gassmann F, Schimmelpfennig B, Klo by means of bipolar radio-frequency endodiathermy. J Cataract Refract Surg 1988; 14:673–676 €ti R. Vordere Hochfrequenz(HF)-Kapsulotomie. I. Experi9. Klo mentelle Studie [Anterior high frequency capsulotomy. I. Experimental study]. Klin Monbl Augenheilkd 1992; 200:507–510 10. Radner G, Amon M, Stifter E, Nepp J, Diendorfer G, Mallinger R, Radner W. Tissue damage at anterior capsule edges after continuous curvilinear capsulorhexis, high-frequency capsulotomy, and erbium:YAG laser capsulotomy. J Cataract Refract Surg 2004; 30:67–73 11. Aron-Rosa DS, Aron JJ. Effect of preoperative YAG laser anterior capsulotomy on the incidence of posterior capsule opacification: ten year follow-up. J Cataract Refract Surg 1992; 18: 559–561
12. Panda A, Pattnaik NK. Neodymium:yttrium aluminum garnet laser anterior capsulotomy. Ann Ophthalmol 1991; 23:334–336 13. Chambless WS. Neodymium:YAG laser anterior capsulotomy and a possible new application. Am Intra-Ocular Implant Soc J 1985; 11:33–34 14. Richburg FA. Neodymium: YAG laser for anterior capsulotomy. Am Intra-ocular Implant Soc J 1985; 11:372–375 15. O’Donnell FE Jr. YAG anterior capsulotomy avoids anterior radial tears [letter]. J Cataract Refract Surg 1989; 15: 600–601 16. Lin Z, Li S. Comparison of the effectiveness between anterior capsulotomy with Nd:YAG laser and with bent needle in patients with congenital cataract. Yan Ke Xue Bao 1991; 7: 125–127; 124 17. Nagy Z, Takacs A, Filkorn T, Sarayba M. Initial clinical evaluation of an intraocular femtosecond laser in cataract surgery. J Refract Surg 2009; 25:1053–1060 18. Hayashi K, Hayashi H, Nakao F, Hayashi F. Correlation between pupillary size and intraocular lens decentration and visual acuity of a zonal-progressive multifocal lens and a monofocal lens. Ophthalmology 2001; 108:2011–2017 19. Altmann GE, Nichamin LD, Lane SS, Pepose JS. Optical performance of 3 intraocular lens designs in the presence of decentration. J Cataract Refract Surg 2005; 31:574–585
OTHER CITED MATERIAL A. Talamo JH, “Refractive Cataract Surgery with a Femtolaser,” presented at the annual meeting of the American Academy of Ophthalmology, San Francisco, California, USA, October 2009 B. Nagy Z, “One-Year Clinical Experience With a New Femtosecond Laser for Refractive Cataract Surgery,” presented at the annual meeting of the American Academy of Ophthalmology, San Francisco, California, USA, October 2009 C. Nichamin LD, “Laser Capsulotomy With the LensAR Laser System (LLS),” presented at the annual meeting of the American Academy of Ophthalmology, San Francisco, California, USA, October 2009 D. Naranjo-Tackman R, “Novel Uses of a Femtosecond Laser,” presented at the annual meeting of the American Academy of Ophthalmology, San Francisco, California, USA, October 2009
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First author: Ramon Naranjo Tackman, MD Corneal and Refractive Surgery, National University of Mexico and Panamerican University School of Medicine, Mexico City, Mexico