With the evolution of cataract surgery, the postoperative goals have undergone a transition from vision restoration to achieving emmetropia. Significant advancements have been made with respect to intraocular implants and cataract surgery techniques. Higher patient and surgeon expectations for spectacle independence have led to an unofficial acceptance of cataract surgery as a refractive procedure.1 Presbyopia-correcting intraocular lenses (IOLs) have been a significant part of this evolution. Various multifocal designs have been extensively studied with excellent results.2–5 Although these IOLs have provided patients with a greater range of unaided vision, they remain limited by the compromise of light distribution for distance or near focus, which may lead to photic phenomenon such as glare or halos. These effects may be further exaggerated by IOL decentration and tilt.6
Parallel to the development of these implants, a progressive improvement has occurred in the instrumentation and technique of cataract surgery. Laser cataract surgery is the most recent addition to this evolution. Femtosecond lasers can perform several steps during cataract surgery. These have been shown to produce superior incisions, more regular and predictable capsulotomies, along with a decrease in ultrasound power used for nuclear fragmentation.7–10 It is yet to be proven, however, whether these technical advances translate into improved visual and refractive outcomes.
This study was conducted on initial and consecutive cohorts of patients who underwent laser cataract surgery and implantation of the ReSTOR SN6AD1 (Alcon Laboratories Inc, Ft Worth, Texas) IOL with the aim to evaluate the refractive performance of this procedure as compared to manual phacoemulsification cataract surgery.
Patients and Methods
All patients undergoing femtosecond laser cataract surgery at our center between May and July 2011 were enrolled in this study. Consecutive patients undergoing laser cataract surgery (Alcon LenSx Inc, Aliso Viejo, California) along with ReSTOR SN6AD1 IOL implantation were initially selected. Cases with other coexisting ocular pathology, topographic astigmatism >1.00 diopter (D), prior refractive surgery, or with intraoperative arcuate corneal incisions were excluded from the study. To exclude refractive outliers, the range of preoperative spherical equivalent refraction was limited to ⩽4.00 D of both myopia and hyperopia. The control group was selected from a retrospective cohort of patients who had undergone manual phacoemulsification and ReSTOR SN6AD1 IOL implantation immediately prior to the beginning of laser cataract surgery at our center who also satisfied these criteria. Control patients completed surgery between December 2010 and April 2011. Both eyes of patients, if eligible, were included in the study. This study was part of a prospective, multicenter, nonrandomized evaluation. The study conformed to the tenets of Declaration of Helsinki and was approved by a local human ethics research committee. All patients signed a written informed consent prior to the surgical procedure.
Preoperative evaluation included a comprehensive clinical assessment. Snellen uncorrected (UDVA) and corrected distance visual acuity (CDVA) were evaluated. Uncorrected (UNVA) and corrected near visual acuity (CNVA) were recorded according to the Revised Jaeger Standard notation. All patients were subjected to slit-lamp microscopy and tonometry. Investigations included biometry (IOLMaster version 5; Carl Zeiss Meditec, Jena, Germany); pachymetry, corneal topography, and lens densitometry (Allegro Oculyzer; WaveLight AG, Erlangen, Germany); specular microscopy (EM-3000; Tomey USA, Phoenix, Arizona); and optical coherence tomography for macular thickness (Stratus OCT, Carl Zeiss Meditec). The standard cataract surgery protocol followed at our center includes instillation of ketolorac tromethamine (Acular; Allergan Inc, Irvine, California) four times daily for 3 days before surgery. Visual acuity was converted to decimal notation to allow for statistical comparison.
All procedures were performed under topical anesthesia with 0.4% oxybuprocaine. Preoperatively, 1% tropicamide, 10% phenylephrine, and 1% cyclopentolate (Minims; Chauvin Pharmaceuticals, Surrey, United Kingdom) were instilled for pupillary dilation. The surgeries were performed by four surgeons (M.L., G.S., T.V.R., C.C.).
The LenSx laser system (Alcon LenSx Inc) was used for all femtosecond cataract surgeries. The laser procedure first included programming of lens fragmentation, capsulotomy, and incision patterns for the patient’s eye, which was followed by docking a disposable patient interface to the individuals’s eye. After the selection of anterior capsular offset, lens offset, and corneal wound tunnel lengths on a live microscopic OCT image, the laser energy was delivered. The energy settings used were proprietary—capsulotomy: 13 to 14 μJ, spot/layer separation: 4/3 μm; lens fragmentation: 15 μJ, spot/layer separation: 8/7 μm; primary and secondary corneal incisions: 6.7 μJ, spot/layer separation: 6/6 μm based on surgeon experience.10 Patients were then moved to the operating theater. All cases underwent clear corneal temporal phacoemulsification. Under strict aseptic precautions, the corneal incisions were opened with a Slade spatula (ASICO, Westmont, Illinois). The following steps included lifting of the capsulotomy flap and nuclear phacoemulsification (Infinity Vision System Unit, Alcon Laboratories Inc). The surgery was completed with insertion of a foldable IOL (AcrySof ReSTOR SN6AD1) into the capsular bag.
Postoperative medications included one drop each of 0.3% ciprofloxacin (Ciloxan, Alcon Laboratories Inc), ketorolac tromethamine (Acular, Allergan Inc), and 0.1% dexamethasone ophthalmic suspension (Maxidex, Alcon Laboratories Inc) four times daily for 2 weeks. After 2 weeks, the steroid drops were tapered to twice daily for another week. Follow-up was scheduled at 1 day, 14 days, 6 weeks, and 12 weeks after surgery. At each postoperative visit, patients underwent UDVA, CDVA, and distance-corrected near visual acuity (DCNVA) examination, tonometry, and slit-lamp microscopy.
Intraocular lens powers were calculated using the Holladay IOL consulting program (Holladay Consulting Inc, Bellaire, Texas). The IOL constant utilized had previously been optimized for the SN6AD1 IOL under manual surgery conditions only. These values were recomputed based on the current study data and postoperative refractive results obtained for the patients studied. The new, optimized IOL constants were used to calculate hypothetical refractive prediction errors in patients undergoing laser cataract surgery.
Statistical analysis was performed using SPSS software version 19.0 (SPSS Inc, Chicago, Illinois). Mann-Whitney analysis was used to compare groups across preoperative visual, refractive, and biometric parameters. Student t test was used to compare the values of pre- and postoperative examinations. Kruskall-Wallis test was used where both groups differed significantly preoperatively. Comparison of proportions was done using chi-square analysis. Significance was set at P<.05 although Bonferroni adjustment was performed to protect against type 1 errors across multiple analyses.
The study initially included 90 eyes with laser cataract surgery (LCS group) and 46 eyes that had manual phacoemulsification cataract surgery (MCS group), although due to the existing exclusion criteria these numbers were reduced (61 and 29, respectively). Both groups underwent ReSTOR SN6AD1 IOL implantation during surgery. Table 1 shows a comparison of demographic and preoperative values across the two groups included in the study. Both groups were well matched for visual and refractive parameters. The surgery was successfully completed in all eyes without intraoperative complications.
Table 1: Comparison of Preoperative Clinical and Investigative Parameters Between Eyes Undergoing Laser Cataract Surgery and Manual Cataract Surgery
No significant postoperative refractive differences were noted (Table 2). No eyes in either group showed loss of CDVA during the follow-up period.
Table 2: Comparison of Visual and Refractive Outcomes 3 Months After Cataract Surgery and IOL Implantation
Figure 1 presents a scatterplot of attempted versus achieved spherical equivalent refraction after laser cataract surgery and manual phacoemulsification. Both procedures showed good refractive predictability.
Figure 1. Attempted vs achieved spherical equivalent refraction (SE) between A) laser cataract surgery (LCS) and B) manual phacoemulsification surgery.
Mean postoperative UDVA for the LCS group was 0.87±0.15 (∼20/25) and 0.83±0.21 (∼20/25) for the MCS group (P=.423). Mean postoperative UNVA values were 0.68±0.12 (∼J3) and 0.71±0.12 (∼J3) for the LCS and MCS groups, respectively (P=.193). Figure 2 elaborates the comparative distribution of postoperative UDVA and UNVA among the two groups at 3 months. Functionally, no significant differences were noted overall for UDVA postoperatively (UDVA 20/20 [P=.189], 20/25 [P=.024], 20/30 or better [P=.547]; UNVA N5 [P=.389), N6 [P=.315], N8 or less [P=1.000]).
Figure 2. Comparison of 3-month postoperative A) uncorrected distance visual acuity and B) uncorrected near visual acuity between groups.
The ongoing study data were used to recompute the IOL constants separately for the eyes undergoing laser cataract surgery and manual phacoemulsification surgery using the Holladay IOL consulting program. The respective optimized anterior chamber depth (ACD), personalized ACD (pACD), and surgeon factor (SF) values noted were 119.12, 5.49, and 1.77, respectively, for the MCS group. The corresponding values were 119.30, 5.55, and 1.91, respectively, for the LCS group.
Using the new optimized IOL constant for laser cataract surgery eyes, the hypothetical mean absolute error (MAE) was 0.22±0.19 D (range: 0.00 to 0.88 D) and mean arithmetic error was −0.01±0.29 D (range: −0.88 to 0.68 D). No significant difference was noted between the actual and hypothetical MAE (P=.293) or the mean actual and hypothetical arithmetic errors (P=.180).
Since the introduction of the femtosecond laser for cataract surgery, evidence has accumulated suggesting an improvement in capsulotomy shape, size, and centration, and a better IOL/anterior capsule overlap as compared to manual capsulorrhexis.8–11 The lens fragmentation produced by femtosecond lasers has also been shown to reduce intraoperative ultrasound energy utilization.8 Femtosecond laser–created corneal incisions have been reported to be more stable due to more reproducible generation of squared incisions and multiplanar configuration.7 However, as with any other technological introduction, a distinct learning curve is associated with the use of this innovative procedure, which seems to flatten with adjustment to surgical technique and experience.12,13 For some surgeons, even during the learning phase, with evolving technology, laser cataract surgery can provide a decreased incidence of anterior capsular tears compared with manual surgery.14
In this study, we evaluated the results of a consecutive initial series of laser cataract surgery cases performed as the laser system software and our surgical technique evolved with experience. It must be noted that the manual group in our study represented a highly refined surgical group, where cases had been operated using optimized constants for each surgeon, with results well above the benchmark standards for refractive outcome after cataract surgery in the English National Health Service and according to the 2004 biometry guidelines of the Royal College of Ophthalmologists.15 Despite the early learning curve in understanding the difference between “laser phacoemulsification” and “manual phacoemulsification,” the two groups showed comparable outcomes in terms of visual acuity with no statistically significant difference with respect to mean postoperative sphere, cylinder, and spherical equivalent refraction. Miháltz et al16 published similar results with no significant difference noted in UDVA and CDVA in eyes undergoing continuous curvilinear capsulorrhexis and femtosecond laser–assisted capsulotomy. In a recent prospective randomized study, Kránitz et al17 noted that femtosecond laser capsulotomies are associated with better CDVA. It must be noted that in both our results and those by Miháltz et al, treatment as well as control cohorts had excellent postoperative outcomes exceeding those of Kránitz et al, thereby reducing the probability of achieving statistical significance.
Recently, laser cataract surgery has been shown to produce better visual quality due to decreased vertical tilt and coma, and hence internal aberrations.17 We did not specifically study these metrics in our study. Intraocular lens decentration and tilt can significantly affect the visual performance of an IOL, especially the newer generation IOLs.18,19 Using simulated models, Holladay et al18 identified cut-offs of tilts up to 7° and decentration up to 0.4 mm for optimal performance of an aspheric IOL. In another theoretical study, Piers et al20 gave more liberal acceptable limits of IOL tilt and IOL decentration for desirable visual benefits of an aspheric IOL (10° and 0.9 mm, respectively). In a comparative study, Hayashi et al6 noted that greater decentration correlates with poorer intermediate and distance visual acuity in eyes with multifocal IOLs; however, the same did not influence vision in eyes with monofocal IOLs. Intraocular lens decentration and tilt may affect the distribution of light between distance and near foci, resulting in suboptimal performance of the multifocal IOL. The more precise sizing and centering of femtosecond laser–created capsulotomies result in better IOL/anterior capsule overlap parameters. This may result in better IOL centration as compared to manual continuous curvilinear capsulorrhexis as shown by Kránitz et al.21 Although no statistically significant differences were noted between groups, a greater percentage of eyes achieved 20/25 or better UDVA in the laser cataract surgery group as compared to the manual phacoemulsification group, despite similar refractive outcomes. This trend may be reflected partially by the IOL centration achieved with femtosecond laser–created capsulotomies; however, further evidence is required for confirmation.
Norrby22 published the sources of error influencing the refractive performance of cataract surgery, the most important being preoperative estimation of postoperative IOL position. Optimization of IOL constants reduces postoperative mean absolute errors. It has been noted that IOL constant errors in excess of 0.09 for the Hoffer Q, 0.09 for the Holladay 1, and 0.15 for the SRK/T formulae produced inferior outcomes.23 In this study, we used IOL constants optimized previously for SN6AD1 IOL implantation following routine phacoemulsification surgery at our center. The study data were used to further optimize the IOL constants for femtosecond laser cataract surgery. The differences in optimized A, pACD, and SF values for the LCS and MCS groups were noted to be in excess of the recommended values.23 We calculated the hypothetical MAE and mean arithmetic errors using the new optimized IOL constants. No significant difference was noted between the groups with respect to MAE or the mean arithmetic error although both showed an improvement as would be expected. This is likely a reflection of the excellent results initially. With larger postoperative numbers and refinement of the surgeon factors, the difference may increase with time.
In this small cohort, no significant differences were noted in postoperative mean spherical equivalent refraction and visual acuities between laser cataract surgery performed during learning curve and routine phacoemulsification surgery in eyes undergoing ReSTOR +3.00-D add IOL implantation. This supports the use of laser cataract surgery as an alternative technique to standard cataract surgery in refractive terms. As laser cataract technology and surgical techniques improve, further studies are necessary using optimized IOL constants to assess the visual and refractive results of femtosecond laser cataract surgery.
- Rosen E. Cataract surgery is refractive surgery. J Cataract Refract Surg. 2012;38(2):191–192. doi:10.1016/j.jcrs.2011.12.015 [CrossRef]
- Madrid-Costa D, Cerviño A, Ferrer-Blasco T, García-Lázaro S, Montés-Micó R. Visual and optical performance with hybrid multifocal intraocular lenses. Clin Exp Optom. 2010;93(6):426–440. doi:10.1111/j.1444-0938.2010.00518.x [CrossRef]
- Santhiago MR, Wilson SE, Netto MV, et al. Visual performance of an apodized diffractive multifocal intraocular lens with +3.00-D addition: 1-year follow-up. J Refract Surg. 2011;27(12):899–906. doi:10.3928/1081597X-20110816-01 [CrossRef]
- Sun Y, Zheng D, Song T, Liu Y. Visual function after bilateral implantation of apodized diffractive multifocal IOL with a +3.0 or +4.0 D addition. Ophthalmic Surg Lasers Imaging. 2011;42(4):302–307. doi:10.3928/15428877-20110421-02 [CrossRef]
- Petermeier K, Messias A, Gekeler F, Szurman P. Effect of +3.00 diopter and +4.00 diopter additions in multifocal intraocular lenses on defocus profiles, patient satisfaction, and contrast sensitivity. J Cataract Refract Surg. 2011;37(4):720–726. doi:10.1016/j.jcrs.2010.11.027 [CrossRef]
- 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(11):2011–2017. doi:10.1016/S0161-6420(01)00756-4 [CrossRef]
- Masket S, Sarayba M, Ignacio T, Fram N. Femtosecond laser-assisted cataract incisions: architectural stability and reproducibility. J Cataract Refract Surg. 2010;36(6):1048–1049. doi:10.1016/j.jcrs.2010.03.027 [CrossRef]
- Nagy Z, Takacs A, Filkorn T, Sarayba M. Initial clinical evaluation of an intraocular femtosecond laser in cataract surgery. J Refract Surg. 2009;25(12):1053–1060. doi:10.3928/1081597X-20091117-04 [CrossRef]
- Palanker DV, Blumenkranz MS, Andersen D, et al. Femtosecond laser-assisted cataract surgery with integrated optical coherence tomography. Sci Transl Med. 2010;2(58):58ra85. doi:10.1126/scitranslmed.3001305 [CrossRef]
- Friedman NJ, Palanker DV, Schuele G, et al. Femtosecond laser capsulotomy. J Cataract Refract Surg. 2011;37(7):1189–1198. Erratum in J Cataract Refract Surg. 2011;37(9):1742. doi:10.1016/j.jcrs.2011.04.022 [CrossRef]
- Nagy ZZ, Kránitz K, Takacs AI, Miháltz K, Kovács I, Knorz MC. Comparison of intraocular lens decentration parameters after femtosecond and manual capsulotomies. J Refract Surg. 2011;27(8):564–569. doi:10.3928/1081597X-20110607-01 [CrossRef]
- Bali SJ, Hodge C, Lawless M, Roberts TV, Sutton G. Early experience with the femtosecond laser for cataract surgery. Ophthalmology. 2012;119(5):891–899. doi:10.1016/j.ophtha.2011.12.025 [CrossRef]
- Roberts TV, Sutton G, Lawless MA, Jindal-Bali S, Hodge C. Capsular block syndrome associated with femtosecond laser-assisted cataract surgery. J Cataract Refract Surg. 2011;37(11):2068–2070. doi:10.1016/j.jcrs.2011.09.003 [CrossRef]
- Lawless M, Hodge C. Femtosecond laser cataract surgery: an experience from Australia. Asia-Pacific Journal of Ophthalmology. 2012;1(1):5–10.
- Gale RP, Saldana M, Johnston RL, Zuberbuhler B, McKibbin M. Benchmark standards for refractive outcomes after NHS cataract surgery. Eye (Lond). 2009;23(1):149–152. doi:10.1038/sj.eye.6702954 [CrossRef]
- Miháltz K, Knorz MC, Alió JL, et al. Internal aberrations and optical quality after femtosecond laser anterior capsulotomy in cataract surgery. J Refract Surg. 2011;27(10):711–716. doi:10.3928/1081597X-20110913-01 [CrossRef]
- Kránitz K, Miháltz K, Sándor GL, Takacs A, Knorz MC, Nagy ZZ. Intraocular lens tilt and decentration measured by Scheimpflug camera following manual or femtosecond laser-created continuous circular capsulotomy. J Refract Surg. 2012;28(4):259–263. doi:10.3928/1081597X-20120309-01 [CrossRef]
- Holladay JT, Piers PA, Koranyi G, van der Mooren M, Norrby NE. A new intraocular lens design to reduce spherical aberration of pseudophakic eyes. J Refract Surg. 2002;18(6):683–691.
- Baumeister M, Bühren J, Kohnen T. Tilt and decentration of spherical and aspheric intraocular lenses: effect on higher-order aberrations. J Cataract Refract Surg. 2009;35(6):1006–1012. doi:10.1016/j.jcrs.2009.01.023 [CrossRef]
- Piers PA, Weeber HA, Artal P, Norrby S. Theoretical comparison of aberration-correcting customized and aspheric intraocular lenses. J Refract Surg. 2007;23(4):374–384.
- Kránitz K, Takacs A, Miháltz K, Kovács I, Knorz MC, Nagy ZZ. Femtosecond laser capsulotomy and manual continuous curvilinear capsulorrhexis parameters and their effects on intraocular lens centration. J Refract Surg. 2011;27(8):558–563. doi:10.3928/1081597X-20110623-03 [CrossRef]
- Norrby S. Sources of error in intraocular lens power calculation. J Cataract Refract Surg. 2008;34(3):368–376. doi:10.1016/j.jcrs.2007.10.031 [CrossRef]
- Aristodemou P, Knox Cartwright NE, Sparrow JM, Johnston RL. Intraocular lens formula constant optimization and partial coherence interferometry biometry: refractive outcomes in 8108 eyes after cataract surgery. J Cataract Refract Surg. 2011;37(1):50–62. doi:10.1016/j.jcrs.2010.07.037 [CrossRef]
Comparison of Preoperative Clinical and Investigative Parameters Between Eyes Undergoing Laser Cataract Surgery and Manual Cataract Surgery
||LCS Group (n=61)
||MCS Group (n=29)
||0.88±0.19 (0.13 to 1.0)
||0.87±0.17 (0.5 to 1.0)
||1.64±1.36 (−3.25 to +3.75)
||1.70±0.72 (0.5 to +3.25)
||−0.52±0.34 (−1.25 to 0.00)
||−0.33±0.23 (−0.75 to 0.00)
||1.38±1.35 (−3.25 to +3.63)
||1.53±0.68 (+0.38 to +3.13)
|Mean keratometry (D)
||43.63±1.27 (40.94 to 46.11)
||43.38±1.16 (41.32 to 45.77)
|Mean keratometry cylinder (D)
||0.52±0.25 (0.00 to 0.93)
||0.51±0.26 (0.00 to 0.98)
|IOL power (D)
||22.34±2.03 (17.00 to 26.00)
||22.36±2.06 (17.50 to 25.00)
Comparison of Visual and Refractive Outcomes 3 Months After Cataract Surgery and IOL Implantation
||LCS Group (n=61)
||MCS Group (n=29)
||0.87±0.15 (0.50 to 1.25)
||0.83±0.21 (0.40 to 1.25)
||0.98±0.09 (0.67 to 1.25)
||1.00±0.06 (0.40 to 1.25)
||0.68±0.12 (0.32 to 1.00)
||0.71±0.12 (0.63 to 1.00)
||0.20±0.39 (−0.75 to +1.25)
||0.16±0.32 (−0.5 to +0.75)
||−0.43±0.33 (−1.25 to 0.00)
||−0.44±0.38 (−1.00 to 0.00)
||−0.01±0.35 (−1.13 to 0.88)
||−0.06±0.30 (−0.63 to 0.50)
|Mean absolute error (D)
||0.26±0.25 (−0.10 to 1.18)
||0.23±0.16 (0.00 to 0.52)
|Mean arithmetic error (D)
||0.06±0.35 (−1.18 to 0.98)
||0.03±0.28 (−0.50 to 0.52)