- Email: [email protected]
Comparison of surgically induced astigmatism between femtosecond laser and manual clear corneal incisions for cataract surgery
ARTICLE
Comparison of surgically induced astigmatism between femtosecond laser and manual clear corneal incisions for cataract surgery Vasilios F. Diakonis, MD, PhD, Nilufer Yesilirmak, MD, Florence Cabot, MD, Vardhaman P. Kankariya, MD, George A. Kounis, PhD, Daniel Warren, MSc, Ibrahim O. Sayed-Ahmed, MD, Sonia H. Yoo, MD, Kendall Donaldson, MD, MS
PURPOSE: To assess the surgically induced corneal astigmatism (SIA) introduced by femtosecond laser–assisted clear corneal incisions (CCIs) for cataract extraction and to compare it with the SIA of manually created CCIs. SETTING: Bascom Palmer Eye Institute, Miller School of Medicine, Miami, Florida, USA. DESIGN: Prospective nonrandomized comparative case series. METHODS: Eyes received femtosecond laser–assisted CCIs (Group 1) or manual CCIs (Group 2). The surgical plan included 1 primary and 1 secondary port; the sites of the incisions were the same in both groups and were diametrically opposed between the right eye and left eye. The SIA was assessed using the preoperative and 1-month postoperative keratometric values obtained from corneal topography examinations. RESULTS: This study included 72 eyes of 68 patients with a mean age of 69.0 years G 9.87 (SD) (range 36 to 90 years). Thirty-six eyes received femtosecond laser–assisted CCIs (Group 1) and 36 received manual CCIs (Group 2). The mean preoperative topographic corneal astigmatism was 1.19 G 0.68 diopters (D) (range 0 to 2.50 D) and 0.92 G 0.63 D (range 0.10 to 2.45 D) for Group 1 and Group 2, respectively, whereas, 1 month after cataract surgery, it was 1.16 G 0.63 D (range 0.20 to 2.57 D) and 0.95 G 0.64 D (range 0.21 to 2.37 D), respectively. Multivariate vector analysis revealed no statistically significant difference between the 2 groups for preoperative astigmatism, postoperative astigmatism, and SIA (P > .05 for all comparisons between Group 1 and Group 2). CONCLUSION: Femtosecond laser–assisted and manual corneal incisions for cataract surgery did not appear to significantly alter corneal astigmatism, whereas they showed comparable SIA. Financial Disclosure: Drs. Yoo and Donaldson are speakers for and consultants to Alcon Surgical, Inc., and Abbott Medical Optics, Inc. No other author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2015; 41:2075–2080 Q 2015 ASCRS and ESCRS
Over the past decade, we have experienced the continued evolution of cataract surgery from simple removal of the lens to a refractive procedure designed to alleviate the patient's dependency on glasses. As cataract surgery has become a refractive procedure, patient's expectations have progressively increased, Q 2015 ASCRS and ESCRS Published by Elsevier Inc.
leaving more room for disappointment when the targeted refractive outcome is not achieved. The introduction of premium intraocular lens (IOL) technology began this evolution. Because in most cases premium IOLs are not covered by insurance and patients pay out of pocket, the patients' expectations increase. The http://dx.doi.org/10.1016/j.jcrs.2015.11.004 0886-3350
2075
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use of femtosecond lasers in cataract surgery has the potential to increase precision and therefore to increase patient satisfaction.1 The main intraoperative factors that play a significant role in post-cataract refractive outcomes include effective lens position (which mainly depends on capsulorhexis size, shape, and centration),2,3 management of preexisting corneal astigmatism (through toric IOLs or limbal relaxing incisions), and the surgically induced corneal astigmatism (SIA) induced by the clear corneal incisions (CCIs).4 Clear corneal incisions in traditional phacoemulsification are known to induce corneal astigmatism. This phenomenon mainly depends on the width, length, and site (distance from visual axis) of the incision.4 In manual surgery, the width of the incision is controlled by the keratome used as it is preset at a constant width; however, the length, the architecture, and the site of the incision vary and may not be reproducible, even between successive cases performed by a single surgeon. Previous studies demonstrate that temporal placement of the primary incision induces less corneal astigmatism in comparison to superior wounds5 since these incisions are usually farther from the visual axis (the horizontal axis of the cornea is larger than the vertical).5 Incision width also has been reported to be a contributing factor in SIA as increased corneal flattening has been linked to larger CCI width.6 Some but not all surgeons include SIA in their nomograms for IOL calculations to achieve optimum refractive results. The use of femtosecond lasers may provide more predictable and reproducible outcomes by inducing a low, predictable degree of astigmatism through the creation of lasercreated CCIs.7–9 Femtosecond laser–assisted CCI creation has high precision and reproducibility because all the parameters (width, length, site, and incision architecture) may be controlled and executed with submicron accuracy.7–9 This study prospectively assessed the preoperative and postoperative topographic outcomes and evaluated the CCI-induced astigmatism after using identical settings for femtosecond laser–assisted CCI creation as a pretreatment in cataract extraction and compared them with manual CCI outcomes. Submitted: January 30, 2015. Final revision submitted: March 5, 2015. Accepted: April 5, 2015. From the Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida, USA. Corresponding author: Vasilios F. Diakonis, MD, PhD, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, 900 Northwest 17 Street, Miami, Florida 33136, USA. E-mail: [email protected].
PATIENTS AND METHODS Patient Population This study included consecutive eyes of patients scheduled to have femtosecond laser–assisted cataract surgery at the Bascom Palmer Eye Institute, Miami, Florida, USA, between June 2014 and December 2014. The Lensx (Alcon Surgical Inc.) platform was used in all cases. The eyes received either femtosecond laser–assisted (Group 1) or manual (Group 2) CCIs, starting with femtosecond and alternating case to case. All patients were informed of risks and benefits prior to cataract surgery, and they gave their written informed consent in accordance with institutional guidelines and the Declaration of Helsinki for human research. Prior to the study, an institutional review board approval was obtained.
Inclusion and Exclusion Criteria The patients included in the study had an unremarkable ocular history. Patients with previous ocular surgery were excluded from the study. Patients with corneal opacities, corneal dystrophies, keratoconus, pellucid marginal degeneration, or abnormal corneal astigmatic pattern were not included in the study. Patients who were initially included were excluded if they had intraoperative or postoperative complications.
Surgical Technique All procedures were performed under topical anesthesia. A femtosecond laser–assisted pretreatment including 2 CCIs (1 primary and 1 secondary) was performed in eyes in Group 1, whereas eyes in Group 2 received manual CCIs. Capsulotomy and phacofragmentation were performed in all eyes using the femtosecond laser, followed by traditional phacoemulsification (Infiniti, Alcon Surgical, Inc.). An IOL was placed in the capsular bag in all cases. Postoperatively, all patients received the same treatment comprising a combination of an antibiotic, steroid, and nonsteroidal antiinflammatory agent.
Clear Corneal Incisions The surgical plan included 1 primary (main) and 1 secondary (side) port in all eyes. The sites of the primary and secondary incisions were the same in both groups and were diametrically opposed between the right and left eyes having surgery. Femtosecond Laser–Assisted Clear Corneal Incisions In Group 1, all CCIs were performed using the same femtosecond laser settings in all eyes; the primary incision was located at 200 degrees in the right eyes and 20 degrees in the left eyes, the width was 2.4 mm, the length was 1.4 mm, and the offset from the limbus was 0.1 mm. The secondary incision was located at 120 degrees in the right eyes and 300 degrees in the left eyes (80 degrees away from the main port, clockwise), the width was 1.0 mm, the length was 1.5 mm, and the offset from the limbus was 0.1 mm. The primary incisions followed the same 3-step architecture (internal contour) with an anterior side-angle of 90 degrees and a posterior side-cut angle of 90 degrees, whereas the lamellar portion of the incision was located at 55% depth of the local corneal thickness. The secondary incisions were 1-plane corneal incisions oriented parallel to the iris surface.
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2.50 D) and 0.92 G 0.63 D (range 0.10 to 2.45 D) in Group 1 and Group 2, respectively, whereas, 1 month after cataract surgery it was 1.16 G 0.63 D (range 0.20 to 2.57 D) and 0.95 G 0.64 D (range 0.21 to 2.37 D), respectively. The keratometry outcomes (steep and flat) in both groups preoperatively and 1 month postoperatively are shown in Table 1. The mean preoperative, postoperative, and surgically induced refractions for both groups based on vector analysis are shown in Table 2. Preoperative, postoperative, and SIA between the groups using multivariate vector analysis did not demonstrate statistical significance (P O .05 for all comparisons between Group 1 and Group 2). Figures 1 and 2 demonstrate double-vector diagrams of preoperative astigmatism and SIA (preoperative minus postoperative corneal astigmatism) for all patients in the study. Since the intended SIA deriving from the CCI is minimal, the SIA outcomes on the graphs are concentrated around the zero area.
Manual Clear Corneal Incisions In Group 2, the manual primary incisions were performed at the same locations in both right and left eyes as described in Group 1 and were targeted to follow a 3-step architecture. The keratome blade used (Xstar Safety Slit Knife, Beaver-Visitec International Inc.) was 2.5 mm in width, and the incision length was guided using the engraved marking on the blade (located 2.0 mm behind the blade's tip) as the blade was angled downward through the cornea and into the anterior chamber at that mark, making the length of the incision approximately 2.0 mm. The manual secondary incisions were performed at the same locations in both right and left eyes as described in Group 1 and followed a “stab-like” architecture (parallel to the iris surface); the keratome blade used (Safety Sideport Knife, Beaver-Visitec International Inc.) was 1.15 in width and the length was about 1.5 larger than the width going up to 1.5 mm.
Patient Assessment Placido-based corneal topography (TMS 4, Tomey Corp.) was performed on all patients before surgery and 1 month after surgery to assess the steep and flat keratometric (K) values and their axes, along with the magnitude of corneal astigmatism preoperatively and 1 month postoperatively. Preoperative topography was performed no more than 1 week before surgery.
DISCUSSION Any new technology must be compared with the accepted standard of care and to succeed must exceed the standard in some way. Femtosecond laser–assisted cataract surgery is no different as the stages of the procedure are being examined individually so that surgeons and patients may make better treatment decisions. Fortunately, traditional cataract surgery with ultrasound (US) technology is extremely safe and yields very good refractive outcomes, making it more difficult to exceed the standard in some respects.13 However, there is always some room for improvement from a standpoint of safety, efficiency, and refractive outcomes. The creation of CCIs with femtosecond laser–assisted cataract surgery has been a point of controversy, with many surgeons still electing to make their incisions manually and to use the femtosecond laser only for capsulotomy creation and lens fragmentation. Some of the controversies regarding the CCI include questions over incidental reports of persistent
Statistical Analysis Excel software (2007, Microsoft Corp.) and a customized ophthalmic data-analysis softwareA were used for data collection and analysis. Preoperative and postoperative topographic values were analyzed by means of multivariate vector analysis to assess the SIA introduced by femtosecond laser–assisted and manual CCIs as described by Kaye and Harris10 and Thibos et al.11 Induced astigmatism is presented by double-angle vector diagrams.12 Multivariate analysis of variance was performed, and a P value lower than 0.05 was considered statistically significant.
RESULTS This prospective study included 72 eyes of 68 patients. The mean age of the 26 men and 42 women was 69.0 years G 9.87 (SD) (range 36 to 90 years). Thirtysix eyes received femtosecond laser–assisted CCIs (Group 1), and 36 received manual CCIs (Group 2). The mean preoperative topographic corneal astigmatism was 1.19 G 0.68 diopters (D) (range 0 to
Table 1. Mean K values (steep and flat) along with mean axis in both groups preoperatively and 1 month postoperatively. Mean G SD Femtosecond CCI: Group 1 Stage Preop Postop
Manual CCI: Group 2
Steep K
Flat K
Axis ( )
Steep K (D)
Flat K (D)
Axis ( )
44.29 G 1.99 44.18 G 1.92
43.10 G 1.80 43.02 G 1.75
76.08 G 5.25 97.94 G 47.48
44.16 G 1.45 44.09 G 1.31
43.24 G 1.56 43.14 G 1.40
94.22 G 61.07 107 G 48.19
CCI Z clear corneal incisions; K Z keratometry
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Table 2. Mean preoperative, postoperative, and surgically induced refractions based on vector analysis. Refraction Type Group 1 Preoperative Postoperative Surgically induced Group 2 Preoperative Postoperative Surgically induced
Sphere (D)
Cylinder (D)
Axis ( )
M (D)
J0 (D)
J45 (D)
0.59 0.58 0.09
0.03 0.06 0.11
0.04 0.07 0.17
0.55 0.48 0.29
0.10 0.20 0.41
118 25 152
0.46 0.47 0.09
0.04 0.04 0.06
0.02 0.08 0.07
0.41 0.38 0.18
0.09 0.19 0.19
78 31 157
J0 Z power of a vertical Jackson cross-cylinder; J45 Z power of an oblique Jackson cross-cylinder; M Z spherical equivalent refraction; SE Z spherical equivalent
temporal edema around the wound and difficulties with wound closure in some cases. Some of these issues stem from limitations in imaging resulting in CCIs that were being placed more anteriorly than intended, potentially inducing either regular or irregular astigmatism. As the imaging capabilities of the various laser platforms have continued to improve, our ability to make incisions more peripheral, closer to the limbus, has helped us avoid this potential problem. Since the femtosecond lasers are unable to cut through opaque tissues, surgeons who typically begin their incisions in the sclera have to move their incisions entirely onto the clear cornea. The primary concern about our CCI wound construction is the relationship
between secure wound closure and endophthalmitis prevention.14 Secondarily, temporal wound edema may lead to delayed visual recovery, which lessens patient satisfaction. There are some differences between the commercially available laser platforms (ie, applanation versus liquid interfaces) with regard to the creation of CCIs. Determining the proper laser parameters to design an effective corneal wound with proper wound placement can avoid issues with wound leakage in most cases. Two types of incisions, CCIs and limbal-relaxing incisions, may be created during cataract surgery, either manually or with the femtosecond laser. To date, data are few comparing laser and manual
Figure 1. Double-vector diagram demonstrating the preoperative corneal astigmatism (red dots) of all patients in the femtosecond group (Group 1) and the SIA group (green dots) deriving from the CCIs.
Figure 2. Double-vector diagram demonstrating the preoperative corneal astigmatism (red dots) of all patients in the manual group (Group 2) and the SIA group (green dots) deriving from the CCIs.
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incisions in each of these subgroups. It is universally accepted that femtosecond lasers are able to create precisely shaped (internal contour: 3-plane incisions), optimally placed (on any axis), and perfectly sized (width and length of the incision) CCIs during femtosecond laser–assisted cataract surgery. There is some evidence of the superiority of laser-created incisions over manual incisions in patients having astigmatism correction after penetrating keratoplasty.15 However, despite the theoretical benefits of the laser's ability to create more reproducible wound architecture, resulting in lower more predictable SIA and thus improving the efforts of correcting corneal astigmatism during cataract surgery, superiority has not been proven. In today's surgical practice of cataract extraction, optimum management of corneal astigmatism plays a significant role in visual outcomes, especially in cases of premium IOL (eg, multifocal, toric) implantation, in which the presence of corneal astigmatism may lead to suboptimum refractive outcomes and patient dissatisfaction.16,17 Our study demonstrated no significant difference in SIA between femtosecond laser–assisted and manual CCIs. This finding is consistent with previously published studies that performed similar comparisons. Nagy et al.18 and Mastropasqua et al.19 found no significant differences in SIA between manual and femtosecond laser–assisted CCIs. Nevertheless, Nagy et al.18 revealed significantly smaller axis deviation in the femtosecond group, and Mastropasqua et al.19 demonstrated that the keratometric astigmatism was significantly lower in the femtosecond group. Femtosecond laser platforms have the theoretical potential to offer more precise creation of CCIs than manual CCI creation when used by inexperienced surgeons; in the current study, the manual incisions were performed by experienced surgeons, yielding SIA similar to that when the femtosecond laser was used. Clear corneal incision integrity is affected by thermal injury caused by US energy delivery during phacoemulsification and mechanical injury due to surgical instrument maneuvering.20,21 The creation of capsulotomies and lens fragmentation during femtosecond laser–assisted cataract surgery facilitates cataract extraction and thereby minimizes surgical time (maneuvering), which reduces mechanical trauma, and decreases the cumulative dissipated US energy,22 which reduces thermal injury. These advantages that femtosecond laser–assisted cataract surgery demonstrate in comparison with traditional phacoemulsification may prove to result in safer, more predictable, and more efficient CCIs, especially when inexperienced surgeons use femtosecond laser platforms for cataract extraction.
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Even though there was no statistically significant difference in the SIA between the 2 groups in our study, the vector graphs demonstrate a difference. As mentioned in the Results section, the function indications of SIA for all patients in both groups need to concentrate around the zero area. In both groups, this was demonstrated, although the femtosecond laser group had a higher dispersion than the manual group. This may be attributed to the actual placement of the femtosecond laser–assisted CCIs, which are located on clear cornea and thereby may be more proximal to the visual axis (inducing more flattening at the meridian of the incision). On the contrary, manual CCIs most commonly demonstrate a more peripheral entry placed at the limbus and thereby they are more distal to the visual axis than femtosecond laser–assisted CCIs, inducing less flattening at the meridian of the incision. Our study is limited by the small number of eyes included. Furthermore, we only compared the SIA of CCIs performed by the same experienced surgeon (K.E.D.). Nevertheless, our study revealed similar levels of astigmatism induction when comparing femtosecond laser–created CCIs with manual CCIs. This study is ongoing to include larger numbers in each group with comparisons between various laser platforms that have different types of patient interfaces (applanating versus liquid). Femtosecond laser–assisted cataract surgery is a relatively new technology, and we will need to continually evaluate its potential benefits relative to traditional cataract surgery to accurately represent this to our patients.
WHAT WAS KNOWN Clear corneal incisions during cataract surgery induce corneal astigmatism. WHAT THIS PAPER ADDS A comparison between manual CCIs from an experienced surgeon and femtosecond laser–assisted CCIs using vector multivariate analysis showed no significant difference in surgically induced corneal astigmatism.
REFERENCES JL, Abdou AA, Arias Puente A, Zato MA, Nagy Z. Femto1. Alio second laser cataract surgery: updates on technologies and outcomes. J Refract Surg 2014; 30:420–427 2. Donaldson KE, Braga-Mele R, Cabot F, Davidson R, Dhaliwal DK, Hamilton R, Jackson M, Patterson L, Stonecipher K, Yoo SH; for the ASCRS Refractive Cataract Surgery Subcommittee. Femtosecond laser–assisted cataract surgery. J Cataract Refract Surg
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2013; 39:1753–1763. Available at: http://www.ascrs.org/sites/ default/files/resources/Femtosecond%20Cataract%20Surgery% 20Review_0.pdf. Accessed September 6, 2015 Horva Knorz MC, Nagy ZZ. cs I, Taka cs A, th E, Filkorn T, Kova Comparison of IOL power calculation and refractive outcome after laser refractive cataract surgery with a femtosecond laser versus conventional phacoemulsification. J Refract Surg 2012; 28:540–544 Masket S, Wang L, Belani S. Induced astigmatism with 2.2- and 3.0-mm coaxial phacoemulsification incisions. J Refract Surg 2009; 25:21–24 Marek R, Klu s A, Pawlik R. Comparison of surgically induced astigmatism of temporal versus superior clear corneal incisions. Klin Oczna 2006; 108:392–396 Wei Y-H, Chen W-L, Su P-Y, Shen EP, Hu F-R. The influence of corneal wound size on surgically induced corneal astigmatism after phacoemulsification. J Formos Med Assoc 2012; 111:284–289 nitz K, Takacs AI, Miha ltz K, Kova cs I, Knorz MC. Nagy ZZ, Kra Comparison of intraocular lens decentration parameters after femtosecond and manual capsulotomies. J Refract Surg 2011; 27:564–569 Nagy ZZ, Takacs A, Filkorn T, Sarayba M. Initial clinical evaluation of an intraocular femtosecond laser in cataract surgery. J Refract Surg 2009; 25:1053–1060 JL, Abdou AA, Soria F, Javaloy J, Ferna ndez-Buenaga R, Alio Nagy ZZ, Filkorn T. Femtosecond laser cataract incision morphology and corneal higher-order aberration analysis. J Refract Surg 2013; 29:590–595 Kaye SB, Harris WF. Analyzing refractive data. J Cataract Refract Surg 2002; 28:2109–2116 Thibos LN, Wheeler W, Horner D. Power vectors: an application of Fourier analysis to the description and statistical analysis of refractive error. Optom Vis Sci 1997; 74:367–375. Available at: http://journals.lww.com/optvissci/Abstract/1997/06000/Power_ Vectors__An_Application_of_Fourier_Analysis.19.aspx. Accessed September 6, 2015 Alpins NA. A new method of analyzing vectors for changes in astigmatism. J Cataract Refract Surg 1993; 19:524–533 Murphy C, Tuft SJ, Minassian DC. Refractive error and visual outcome after cataract extraction. J Cataract Refract Surg 2002; 28:62–66 Miller JJ, Scott IU, Flynn HW Jr, Smiddy WE, Newton J, Miller D. Acute-onset endophthalmitis after cataract surgery (20002004): incidence, clinical settings, and visual acuity outcomes after treatment. Am J Ophthalmol 2005; 139:983–987
15. Bahar I, Levinger E, Kaiserman I, Sansanayudh W, Rootman DS. IntraLase-enabled astigmatic keratotomy for postkeratoplasty astigmatism. Am J Ophthalmol 2008; 146:897–904 €16. Kohnen T, Kook D, Auffarth GU, Derhartunian V. Einsatzm o glichkeiten intraokularer Multifokallinsen und Kriterien der Patientenselektion [Use of multifocal intraocular lenses and criteria for patient selection]. Ophthalmologe 2008; 105:527–532 17. Hayashi K, Hayashi H, Nakao F, Hayashi F. Influence of astigmatism on multifocal and monofocal intraocular lenses. Am J Ophthalmol 2000; 130:477–482 Kra Sa nitz K, Taka cs AL, ndor GL, He cz R, 18. Nagy ZZ, Dunai A, Knorz MC. Evaluation of femtosecond laser-assisted and manual clear corneal incisions and their effect on surgically induced astigmatism and higher-order aberrations. J Refract Surg 2014; 30:522–525 19. Mastropasqua L, Toto L, Mastropasqua A, Vecchiarino L, Mastropasqua R, Pedrotti E, Di Nicola M. Femtosecond laser versus manual clear corneal incisions in cataract surgery. J Refract Surg 2014; 30:27–33 20. Vasavada V, Vasavada AR, Vasavada VA, Srivastava S, Gajjar DU, Mehta S. Incision integrity and postoperative outcomes after microcoaxial phacoemulsification performed using 2 incision-dependent systems. J Cataract Refract Surg 2013; 39:563–571 21. Bradley MJ, Olson RJ. A survey about phacoemulsification incisions thermal contraction incidence and casual relationships. Am J Ophthalmol 2006; 141:222–224 22. Abell RG, Kerr NM, Vote BJ. Toward zero effective phacoemulsification time using femtosecond laser pretreatment. Ophthalmology 2013; 120:942–948
OTHER CITED MATERIAL A. Kounis GA. Ophthalmic Data & Database. Slide show available at: http://www.slideshare.net/GeorgiosAthKounis/ophthalmic -data-databse. Accessed September 6, 2015.
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First author: Vasilios F. Diakonis, MD, PhD Bascom Palmer Eye Institute, Miller School of Medicine, University of Miami, Miami, Florida, USA
Comparison of surgically induced astigmatism between femtosecond laser and manual clear corneal incisions for cataract surgery Vasilios F. Diakonis, MD, PhD, Nilufer Yesilirmak, MD, Florence Cabot, MD, Vardhaman P. Kankariya, MD, George A. Kounis, PhD, Daniel Warren, MSc, Ibrahim O. Sayed-Ahmed, MD, Sonia H. Yoo, MD, Kendall Donaldson, MD, MS
PURPOSE: To assess the surgically induced corneal astigmatism (SIA) introduced by femtosecond laser–assisted clear corneal incisions (CCIs) for cataract extraction and to compare it with the SIA of manually created CCIs. SETTING: Bascom Palmer Eye Institute, Miller School of Medicine, Miami, Florida, USA. DESIGN: Prospective nonrandomized comparative case series. METHODS: Eyes received femtosecond laser–assisted CCIs (Group 1) or manual CCIs (Group 2). The surgical plan included 1 primary and 1 secondary port; the sites of the incisions were the same in both groups and were diametrically opposed between the right eye and left eye. The SIA was assessed using the preoperative and 1-month postoperative keratometric values obtained from corneal topography examinations. RESULTS: This study included 72 eyes of 68 patients with a mean age of 69.0 years G 9.87 (SD) (range 36 to 90 years). Thirty-six eyes received femtosecond laser–assisted CCIs (Group 1) and 36 received manual CCIs (Group 2). The mean preoperative topographic corneal astigmatism was 1.19 G 0.68 diopters (D) (range 0 to 2.50 D) and 0.92 G 0.63 D (range 0.10 to 2.45 D) for Group 1 and Group 2, respectively, whereas, 1 month after cataract surgery, it was 1.16 G 0.63 D (range 0.20 to 2.57 D) and 0.95 G 0.64 D (range 0.21 to 2.37 D), respectively. Multivariate vector analysis revealed no statistically significant difference between the 2 groups for preoperative astigmatism, postoperative astigmatism, and SIA (P > .05 for all comparisons between Group 1 and Group 2). CONCLUSION: Femtosecond laser–assisted and manual corneal incisions for cataract surgery did not appear to significantly alter corneal astigmatism, whereas they showed comparable SIA. Financial Disclosure: Drs. Yoo and Donaldson are speakers for and consultants to Alcon Surgical, Inc., and Abbott Medical Optics, Inc. No other author has a financial or proprietary interest in any material or method mentioned. J Cataract Refract Surg 2015; 41:2075–2080 Q 2015 ASCRS and ESCRS
Over the past decade, we have experienced the continued evolution of cataract surgery from simple removal of the lens to a refractive procedure designed to alleviate the patient's dependency on glasses. As cataract surgery has become a refractive procedure, patient's expectations have progressively increased, Q 2015 ASCRS and ESCRS Published by Elsevier Inc.
leaving more room for disappointment when the targeted refractive outcome is not achieved. The introduction of premium intraocular lens (IOL) technology began this evolution. Because in most cases premium IOLs are not covered by insurance and patients pay out of pocket, the patients' expectations increase. The http://dx.doi.org/10.1016/j.jcrs.2015.11.004 0886-3350
2075
2076
FEMTOSECOND LASER VERSUS MANUAL CCIS
use of femtosecond lasers in cataract surgery has the potential to increase precision and therefore to increase patient satisfaction.1 The main intraoperative factors that play a significant role in post-cataract refractive outcomes include effective lens position (which mainly depends on capsulorhexis size, shape, and centration),2,3 management of preexisting corneal astigmatism (through toric IOLs or limbal relaxing incisions), and the surgically induced corneal astigmatism (SIA) induced by the clear corneal incisions (CCIs).4 Clear corneal incisions in traditional phacoemulsification are known to induce corneal astigmatism. This phenomenon mainly depends on the width, length, and site (distance from visual axis) of the incision.4 In manual surgery, the width of the incision is controlled by the keratome used as it is preset at a constant width; however, the length, the architecture, and the site of the incision vary and may not be reproducible, even between successive cases performed by a single surgeon. Previous studies demonstrate that temporal placement of the primary incision induces less corneal astigmatism in comparison to superior wounds5 since these incisions are usually farther from the visual axis (the horizontal axis of the cornea is larger than the vertical).5 Incision width also has been reported to be a contributing factor in SIA as increased corneal flattening has been linked to larger CCI width.6 Some but not all surgeons include SIA in their nomograms for IOL calculations to achieve optimum refractive results. The use of femtosecond lasers may provide more predictable and reproducible outcomes by inducing a low, predictable degree of astigmatism through the creation of lasercreated CCIs.7–9 Femtosecond laser–assisted CCI creation has high precision and reproducibility because all the parameters (width, length, site, and incision architecture) may be controlled and executed with submicron accuracy.7–9 This study prospectively assessed the preoperative and postoperative topographic outcomes and evaluated the CCI-induced astigmatism after using identical settings for femtosecond laser–assisted CCI creation as a pretreatment in cataract extraction and compared them with manual CCI outcomes. Submitted: January 30, 2015. Final revision submitted: March 5, 2015. Accepted: April 5, 2015. From the Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida, USA. Corresponding author: Vasilios F. Diakonis, MD, PhD, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, 900 Northwest 17 Street, Miami, Florida 33136, USA. E-mail: [email protected].
PATIENTS AND METHODS Patient Population This study included consecutive eyes of patients scheduled to have femtosecond laser–assisted cataract surgery at the Bascom Palmer Eye Institute, Miami, Florida, USA, between June 2014 and December 2014. The Lensx (Alcon Surgical Inc.) platform was used in all cases. The eyes received either femtosecond laser–assisted (Group 1) or manual (Group 2) CCIs, starting with femtosecond and alternating case to case. All patients were informed of risks and benefits prior to cataract surgery, and they gave their written informed consent in accordance with institutional guidelines and the Declaration of Helsinki for human research. Prior to the study, an institutional review board approval was obtained.
Inclusion and Exclusion Criteria The patients included in the study had an unremarkable ocular history. Patients with previous ocular surgery were excluded from the study. Patients with corneal opacities, corneal dystrophies, keratoconus, pellucid marginal degeneration, or abnormal corneal astigmatic pattern were not included in the study. Patients who were initially included were excluded if they had intraoperative or postoperative complications.
Surgical Technique All procedures were performed under topical anesthesia. A femtosecond laser–assisted pretreatment including 2 CCIs (1 primary and 1 secondary) was performed in eyes in Group 1, whereas eyes in Group 2 received manual CCIs. Capsulotomy and phacofragmentation were performed in all eyes using the femtosecond laser, followed by traditional phacoemulsification (Infiniti, Alcon Surgical, Inc.). An IOL was placed in the capsular bag in all cases. Postoperatively, all patients received the same treatment comprising a combination of an antibiotic, steroid, and nonsteroidal antiinflammatory agent.
Clear Corneal Incisions The surgical plan included 1 primary (main) and 1 secondary (side) port in all eyes. The sites of the primary and secondary incisions were the same in both groups and were diametrically opposed between the right and left eyes having surgery. Femtosecond Laser–Assisted Clear Corneal Incisions In Group 1, all CCIs were performed using the same femtosecond laser settings in all eyes; the primary incision was located at 200 degrees in the right eyes and 20 degrees in the left eyes, the width was 2.4 mm, the length was 1.4 mm, and the offset from the limbus was 0.1 mm. The secondary incision was located at 120 degrees in the right eyes and 300 degrees in the left eyes (80 degrees away from the main port, clockwise), the width was 1.0 mm, the length was 1.5 mm, and the offset from the limbus was 0.1 mm. The primary incisions followed the same 3-step architecture (internal contour) with an anterior side-angle of 90 degrees and a posterior side-cut angle of 90 degrees, whereas the lamellar portion of the incision was located at 55% depth of the local corneal thickness. The secondary incisions were 1-plane corneal incisions oriented parallel to the iris surface.
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2.50 D) and 0.92 G 0.63 D (range 0.10 to 2.45 D) in Group 1 and Group 2, respectively, whereas, 1 month after cataract surgery it was 1.16 G 0.63 D (range 0.20 to 2.57 D) and 0.95 G 0.64 D (range 0.21 to 2.37 D), respectively. The keratometry outcomes (steep and flat) in both groups preoperatively and 1 month postoperatively are shown in Table 1. The mean preoperative, postoperative, and surgically induced refractions for both groups based on vector analysis are shown in Table 2. Preoperative, postoperative, and SIA between the groups using multivariate vector analysis did not demonstrate statistical significance (P O .05 for all comparisons between Group 1 and Group 2). Figures 1 and 2 demonstrate double-vector diagrams of preoperative astigmatism and SIA (preoperative minus postoperative corneal astigmatism) for all patients in the study. Since the intended SIA deriving from the CCI is minimal, the SIA outcomes on the graphs are concentrated around the zero area.
Manual Clear Corneal Incisions In Group 2, the manual primary incisions were performed at the same locations in both right and left eyes as described in Group 1 and were targeted to follow a 3-step architecture. The keratome blade used (Xstar Safety Slit Knife, Beaver-Visitec International Inc.) was 2.5 mm in width, and the incision length was guided using the engraved marking on the blade (located 2.0 mm behind the blade's tip) as the blade was angled downward through the cornea and into the anterior chamber at that mark, making the length of the incision approximately 2.0 mm. The manual secondary incisions were performed at the same locations in both right and left eyes as described in Group 1 and followed a “stab-like” architecture (parallel to the iris surface); the keratome blade used (Safety Sideport Knife, Beaver-Visitec International Inc.) was 1.15 in width and the length was about 1.5 larger than the width going up to 1.5 mm.
Patient Assessment Placido-based corneal topography (TMS 4, Tomey Corp.) was performed on all patients before surgery and 1 month after surgery to assess the steep and flat keratometric (K) values and their axes, along with the magnitude of corneal astigmatism preoperatively and 1 month postoperatively. Preoperative topography was performed no more than 1 week before surgery.
DISCUSSION Any new technology must be compared with the accepted standard of care and to succeed must exceed the standard in some way. Femtosecond laser–assisted cataract surgery is no different as the stages of the procedure are being examined individually so that surgeons and patients may make better treatment decisions. Fortunately, traditional cataract surgery with ultrasound (US) technology is extremely safe and yields very good refractive outcomes, making it more difficult to exceed the standard in some respects.13 However, there is always some room for improvement from a standpoint of safety, efficiency, and refractive outcomes. The creation of CCIs with femtosecond laser–assisted cataract surgery has been a point of controversy, with many surgeons still electing to make their incisions manually and to use the femtosecond laser only for capsulotomy creation and lens fragmentation. Some of the controversies regarding the CCI include questions over incidental reports of persistent
Statistical Analysis Excel software (2007, Microsoft Corp.) and a customized ophthalmic data-analysis softwareA were used for data collection and analysis. Preoperative and postoperative topographic values were analyzed by means of multivariate vector analysis to assess the SIA introduced by femtosecond laser–assisted and manual CCIs as described by Kaye and Harris10 and Thibos et al.11 Induced astigmatism is presented by double-angle vector diagrams.12 Multivariate analysis of variance was performed, and a P value lower than 0.05 was considered statistically significant.
RESULTS This prospective study included 72 eyes of 68 patients. The mean age of the 26 men and 42 women was 69.0 years G 9.87 (SD) (range 36 to 90 years). Thirtysix eyes received femtosecond laser–assisted CCIs (Group 1), and 36 received manual CCIs (Group 2). The mean preoperative topographic corneal astigmatism was 1.19 G 0.68 diopters (D) (range 0 to
Table 1. Mean K values (steep and flat) along with mean axis in both groups preoperatively and 1 month postoperatively. Mean G SD Femtosecond CCI: Group 1 Stage Preop Postop
Manual CCI: Group 2
Steep K
Flat K
Axis ( )
Steep K (D)
Flat K (D)
Axis ( )
44.29 G 1.99 44.18 G 1.92
43.10 G 1.80 43.02 G 1.75
76.08 G 5.25 97.94 G 47.48
44.16 G 1.45 44.09 G 1.31
43.24 G 1.56 43.14 G 1.40
94.22 G 61.07 107 G 48.19
CCI Z clear corneal incisions; K Z keratometry
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Table 2. Mean preoperative, postoperative, and surgically induced refractions based on vector analysis. Refraction Type Group 1 Preoperative Postoperative Surgically induced Group 2 Preoperative Postoperative Surgically induced
Sphere (D)
Cylinder (D)
Axis ( )
M (D)
J0 (D)
J45 (D)
0.59 0.58 0.09
0.03 0.06 0.11
0.04 0.07 0.17
0.55 0.48 0.29
0.10 0.20 0.41
118 25 152
0.46 0.47 0.09
0.04 0.04 0.06
0.02 0.08 0.07
0.41 0.38 0.18
0.09 0.19 0.19
78 31 157
J0 Z power of a vertical Jackson cross-cylinder; J45 Z power of an oblique Jackson cross-cylinder; M Z spherical equivalent refraction; SE Z spherical equivalent
temporal edema around the wound and difficulties with wound closure in some cases. Some of these issues stem from limitations in imaging resulting in CCIs that were being placed more anteriorly than intended, potentially inducing either regular or irregular astigmatism. As the imaging capabilities of the various laser platforms have continued to improve, our ability to make incisions more peripheral, closer to the limbus, has helped us avoid this potential problem. Since the femtosecond lasers are unable to cut through opaque tissues, surgeons who typically begin their incisions in the sclera have to move their incisions entirely onto the clear cornea. The primary concern about our CCI wound construction is the relationship
between secure wound closure and endophthalmitis prevention.14 Secondarily, temporal wound edema may lead to delayed visual recovery, which lessens patient satisfaction. There are some differences between the commercially available laser platforms (ie, applanation versus liquid interfaces) with regard to the creation of CCIs. Determining the proper laser parameters to design an effective corneal wound with proper wound placement can avoid issues with wound leakage in most cases. Two types of incisions, CCIs and limbal-relaxing incisions, may be created during cataract surgery, either manually or with the femtosecond laser. To date, data are few comparing laser and manual
Figure 1. Double-vector diagram demonstrating the preoperative corneal astigmatism (red dots) of all patients in the femtosecond group (Group 1) and the SIA group (green dots) deriving from the CCIs.
Figure 2. Double-vector diagram demonstrating the preoperative corneal astigmatism (red dots) of all patients in the manual group (Group 2) and the SIA group (green dots) deriving from the CCIs.
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incisions in each of these subgroups. It is universally accepted that femtosecond lasers are able to create precisely shaped (internal contour: 3-plane incisions), optimally placed (on any axis), and perfectly sized (width and length of the incision) CCIs during femtosecond laser–assisted cataract surgery. There is some evidence of the superiority of laser-created incisions over manual incisions in patients having astigmatism correction after penetrating keratoplasty.15 However, despite the theoretical benefits of the laser's ability to create more reproducible wound architecture, resulting in lower more predictable SIA and thus improving the efforts of correcting corneal astigmatism during cataract surgery, superiority has not been proven. In today's surgical practice of cataract extraction, optimum management of corneal astigmatism plays a significant role in visual outcomes, especially in cases of premium IOL (eg, multifocal, toric) implantation, in which the presence of corneal astigmatism may lead to suboptimum refractive outcomes and patient dissatisfaction.16,17 Our study demonstrated no significant difference in SIA between femtosecond laser–assisted and manual CCIs. This finding is consistent with previously published studies that performed similar comparisons. Nagy et al.18 and Mastropasqua et al.19 found no significant differences in SIA between manual and femtosecond laser–assisted CCIs. Nevertheless, Nagy et al.18 revealed significantly smaller axis deviation in the femtosecond group, and Mastropasqua et al.19 demonstrated that the keratometric astigmatism was significantly lower in the femtosecond group. Femtosecond laser platforms have the theoretical potential to offer more precise creation of CCIs than manual CCI creation when used by inexperienced surgeons; in the current study, the manual incisions were performed by experienced surgeons, yielding SIA similar to that when the femtosecond laser was used. Clear corneal incision integrity is affected by thermal injury caused by US energy delivery during phacoemulsification and mechanical injury due to surgical instrument maneuvering.20,21 The creation of capsulotomies and lens fragmentation during femtosecond laser–assisted cataract surgery facilitates cataract extraction and thereby minimizes surgical time (maneuvering), which reduces mechanical trauma, and decreases the cumulative dissipated US energy,22 which reduces thermal injury. These advantages that femtosecond laser–assisted cataract surgery demonstrate in comparison with traditional phacoemulsification may prove to result in safer, more predictable, and more efficient CCIs, especially when inexperienced surgeons use femtosecond laser platforms for cataract extraction.
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Even though there was no statistically significant difference in the SIA between the 2 groups in our study, the vector graphs demonstrate a difference. As mentioned in the Results section, the function indications of SIA for all patients in both groups need to concentrate around the zero area. In both groups, this was demonstrated, although the femtosecond laser group had a higher dispersion than the manual group. This may be attributed to the actual placement of the femtosecond laser–assisted CCIs, which are located on clear cornea and thereby may be more proximal to the visual axis (inducing more flattening at the meridian of the incision). On the contrary, manual CCIs most commonly demonstrate a more peripheral entry placed at the limbus and thereby they are more distal to the visual axis than femtosecond laser–assisted CCIs, inducing less flattening at the meridian of the incision. Our study is limited by the small number of eyes included. Furthermore, we only compared the SIA of CCIs performed by the same experienced surgeon (K.E.D.). Nevertheless, our study revealed similar levels of astigmatism induction when comparing femtosecond laser–created CCIs with manual CCIs. This study is ongoing to include larger numbers in each group with comparisons between various laser platforms that have different types of patient interfaces (applanating versus liquid). Femtosecond laser–assisted cataract surgery is a relatively new technology, and we will need to continually evaluate its potential benefits relative to traditional cataract surgery to accurately represent this to our patients.
WHAT WAS KNOWN Clear corneal incisions during cataract surgery induce corneal astigmatism. WHAT THIS PAPER ADDS A comparison between manual CCIs from an experienced surgeon and femtosecond laser–assisted CCIs using vector multivariate analysis showed no significant difference in surgically induced corneal astigmatism.
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First author: Vasilios F. Diakonis, MD, PhD Bascom Palmer Eye Institute, Miller School of Medicine, University of Miami, Miami, Florida, USA