Reflection on refraction in multifocal intraocular lenses - Chapter 2: Multifocal intraocular lens implantation after previous corneal refractive laser surgery for myopia

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(1)CHAPTER 2 Multifocal intraocular lens implantation after previous corneal refractive laser surgery for myopia Violette Vrijman, MD Jan Willem van der Linden, BOpt, PhD Ivanka J.E. van der Meulen, MD, PhD Maarten P. Mourits, MD, PhD Ruth Lapid-Gortzak, MD, PhD [J Cataract Refract Surg 2017; Jul;43(7):909–914].

(2) Chapter 2. ABSTRACT Purpose: To describe the refraction and visual acuity outcomes of multifocal intraocular lens (IOL) implantation in patients with previous corneal refractive laser surgery for myopia. Setting: Academic Medical Center, University of Amsterdam, Amsterdam, and Retina Total Eye Care, Driebergen, the Netherlands. Design: Retrospective cohort study. Methods: The 3-month results after implantation of a multifocal IOL (Acrysof Restor) in patients who had corneal refractive laser surgery for myopia were analyzed. The primary outcome measures were corrected distance visual acuity, uncorrected distance visual acuity (UDVA), and refraction. The secondary outcome measures were number of laser enhancements, corneal irregularity, pre-laser magnitude of myopia, and posterior capsule opacification (PCO) rate. Results: Seventy-seven eyes of 43 patients were included. Twenty-nine eyes had lens extraction because of cataract, and 48 eyes had a refractive lens exchange. The mean postoperative UDVA was 0.14 logarithm of minimum angle of resolution ± 0.22 (SD). The mean postoperative spherical equivalent was 0.38 ± 0.78 diopter (D). Fifty-seven percent of eyes were within ±0.50 D of emmetropia, and 86% were within ±1.00 D. Sixteen eyes (20.8%) had laser enhancement because of residual refraction. Fourteen eyes (18.2%) had a neodymium:YAG laser capsulotomy because of PCO. Eyes with pre-laser myopia greater than 6.0 D had a less predictable outcome than eyes with pre-laser myopia less than 6.0 D (P = .026). Conclusions: Multifocal IOL implantation after corneal refractive laser surgery for myopia resulted in good visual acuity and refraction. Results were less predictable with myopia greater than 6.0 D.. 18.

(3) Multifocal IOL after myopic laser surgery. INTRODUCTION Corneal refractive laser surgery is considered a safe procedure with good refractive outcomes.1 Millions of patients have had refractive corneal laser surgery; as they age, these patients will develop presbyopia or cataract. Because they have had refractive surgery, they are likely to see themselves as candidates for another refractive procedure such as multifocal intraocular lens (IOL) implantation. Multifocal IOLs have been successfully implemented in clinical practice and have good effectivity for distance and near visual acuity; the reported visual side effects include decreased contrast sensitivity and halos.2-5 Contraindications for multifocal IOL implantation include glaucoma, retinal pathology, and previous corneal surgery.6 One reason for excluding eyes that have had corneal laser surgery is the assumption that these corneas have been rendered multifocal by the corneal laser procedure and that a multifocal IOL will cause further deterioration of visual function. Another reason is that the postoperative refractive accuracy is undermined by the difficulty of IOL power calculation in eyes that have had corneal laser surgery. This difficulty is caused by 2 factors: (1) inaccurate determination of the total corneal refractive power7 because the ratio between the anterior and posterior curvatures of the cornea is changed by the myopic laser treatment and, possibly, because of a forward shift of the posterior corneal surface8; (2) incorrect estimation of the effective lens position by many IOL calculation formulas when post-laser corneal powers are used.9 In this study, we present the results of multifocal IOL implantation for refractive lens exchange or cataract in a cohort of patients who had corneal refractive laser surgery for myopia. The patients desired spectacle independence, including freedom from presbyopia correction. The visual and refractive results were analyzed, including the number of laser enhancements. Reports of this kind are scarce10-12 due to the controversial indication, the difficulty in IOL power calculation, and possibly because most ophthalmologists have not embraced the use of multifocal IOLs in their practices.. PATIENTS AND METHODS This single-center retrospective study evaluated consecutive eyes with a history of previous corneal refractive laser surgery for myopia that had multifocal IOL implantation for cataract or presbyopia between March 2008 and March 2015 at the Retina Total Eye Care Center (Driebergen, the Netherlands). The study adhered to the tenets of the Declaration of Helsinki and was reviewed by the Medical Ethics Committee of the Academic Medical Center of Amsterdam. Data were gathered prospectively to conform to the consensus of the Dutch Society of Refractive Surgery.A All patients gave signed informed consent preoperatively to use the anonymized data for analysis and scientific publication. 19. 2.

(4) Chapter 2. Inclusion criteria were patients with cataract or presbyopia who had laser refractive surgery for myopia (laser in situ keratomileusis [LASIK], laser-assisted subepithelial keratectomy [LASEK], or photorefractive keratectomy [PRK]) and received an Acrysof Restor multifocal IOL (Alcon Laboratories, Inc.) to resolve the diminished visual acuity or to correct the presbyopia. Exclusion criteria were amblyopia with an initial corrected distance visual acuity (CDVA) of less than 0.1 logarithm of minimum angle of resolution (logMAR), glaucoma, macular disease, a history of retinal detachment, a toric Restor multifocal IOL, and previous corneal disease other than refractive surgery (LASIK, LASEK, PRK). Patient Examinations A full ophthalmic examination was performed before the laser treatment and before and after multifocal IOL implantation. It included uncorrected distance visual acuity (UDVA), CDVA, automated and manifest refraction including spherical equivalent (SE), slitlamp biomicroscopy, tonometry, and dilated indirect fundoscopy. Corneal topography imaging (Orbscan, Bausch & Lomb, Inc.) including the corneal irregularity index and optical biometry (IOLMaster 2 and 5.1, Carl Zeiss Meditec AG) were performed preoperatively. Corneal topography was graded as a prolate or oblate pattern by 2 examiners independently (R.L.-G., V.V.). In most cases, the topography was graded similarly; when it was dissimilar, a definitive grading was made after reexamination of the topography by the 2 examiners together. For IOL calculation, the American Society of Cataract and Refractive Surgery (ASCRS) IOL power calculator9 was used by entering the refractive and keratometry data from before and after the corneal laser treatment, when available, plus the biometric data of the optical biometer. In some cases, contact lens over-refraction was performed. The approach to IOL calculation was not uniform; it has developed over the past 7 years using post-laser calculations. A multiformula approach was generally used, and the choice of IOL was based on the targeted postoperative emmetropia. The data recorded from the corneal refractive surgery were flap diameter, refraction treated, and target refraction. The effect of the amount of pre-laser myopia on the postoperative refractive result was analyzed to determine whether the magnitude of myopia influenced the outcome. The follow-up was a minimum of 1 year. For the primary endpoints, visual and refractive outcomes at 3 months were used. For the secondary outcomes of posterior capsule opacification (PCO) rate and number of corneal laser enhancements, the longest available follow-up data were used. Corneal Refractive Laser Surgery Patients who had corneal laser surgery in our clinic were treated with a Zyoptix 217 Z100 excimer laser (Bausch & Lomb, Inc.), using the Keracor 3.21 Dataware nomogram. Corneal 20.

(5) Multifocal IOL after myopic laser surgery. laser enhancement for residual refraction after the IOL procedure was done using the standard tissue-saving nomogram (Bausch & Lomb, Inc.). Intraocular Lenses An Acrysof Restor SN6AD1 (72 eyes, 93.5%) or SN6AD3 (5 eyes, 6.5%) multifocal IOL was implanted. Both IOLs are single-piece hydrophobic acrylic IOLs with an apodized diffractive multifocal optic that occupies the central 3.6 mm region. Apodization is a gradual decrease in diffractive step heights from the optical center to the periphery. The anterior surface is aspheric.. 2. Surgical Technique Standard phacoemulsification with the Infinity Ozil (Alcon Laboratories, Inc.) was performed under topical anesthesia by 1 of 2 surgeons (R.L.-G., I.J.E.M.) through a 2.2 mm incision. The multifocal IOL was implanted using the Monarch cartridge and Monarch II injector (Alcon Laboratories, Inc.). Statistical Analysis Data were analyzed using SPSS for Windows software (version 22.0, International Business Machines Corp.). The influence of various parameters on the postoperative refractive outcome was evaluated by correlation analysis (Pearson r correlation). Normality was checked with normal probability plots and Kolmogorov-Smirnov and Shapiro-Wilk tests. Depending on normality, a t test or Mann-Whitney U test was used to compare the between-group outcomes. Differences were considered to be statistically significant when the P value was less than 0.05.. RESULTS The study comprised 77 eyes of 43 patients. Table 1 shows the patients’ demographics. Phacoemulsification with implantation of a multifocal IOL was uneventful in all cases. The mean SE after lens extraction and IOL implantation was 0.38 diopters (D) ± 0.78 (SD). The absolute error of the mean SE was 0.61 ± 0.61 D. The mean postoperative UDVA was 0.14 ± 0.22 logMAR and the mean postoperative uncorrected near visual acuity, 0.10 ± 0.10 logMAR. Figure 1 is a histogram of the refractive accuracy. Forty-four eyes (57.1%) were within ± 0.50 D of emmetropia and 66 eyes (85.7%), within ± 1.00 D. Figure 2 shows the attempted versus achieved SE refraction.. 21.

(6) Chapter 2 Demographics. Value. Eyes (n). 77. Number of patients. 43. Sex (male/female). 20/23. Previous LASIK (eyes). 59 (76.6%). Previous LASEK (eyes). 6 (7.8%). Previous PRK (eyes) Indication (cataract/RLE) Mean age at lens extraction ± SD (y). Range. 12 (15.6%) 29/48 58.9 ± 5.6. 49 to 71. Mean pre-laser SE ± SD (D). -4.00 ± 2.25. -10.38 to -0.25. Mean pre-IOL SE ± SD (D). -0.38 ± 1.33. -4.13 to 2.75. Mean pre-IOL mean K value ± SD (D). 40.66 ± 1.82. 35.45 to 45.52. Mean axial length ± SD (mm). 25.34 ± 1.28. 22.91 to 28.95. Mean power implanted IOL ± SD (D). 20.70 ± 2.46. 15.00 to 27.00. Table 1. Patients’ demographics. LASIK = laser in situ keratomileusis, LASEK = laser epithelial keratomileusis, PRK = photorefractive keratectomy, RLE = refractive lens exchange; SD = standard deviation, SE = spherical equivalent.. Figure 1. Refractive accuracy. Fifty-seven percent of eyes were within ± 0.50 D of emmetropia, and 86% were within ± 1.00 D.. 22.

(7) Multifocal IOL after myopic laser surgery. 2. Figure 2. Attempted versus achieved refraction. Green line indicates within ± 0.50 D of the target refraction, and red line within ± 1.00 D.. The efficacy index (ratio of mean postoperative UDVA to mean preoperative CDVA) was 0.81. The safety index (ratio of mean postoperative CDVA to mean preoperative CDVA) was 1.08. The pre-laser SE showed a statistically significant correlation with the refractive outcome (r = 0.313, P = .007). The higher the initial myopia, the more myopic the refractive outcome tended to be. Table 2 shows the effect of the magnitude of pre-laser myopia on the postoperative refractive result. In the table, the patients are divided into 2 groups, those with less than 2.0 D of myopia and those with equal to or greater than 2.0 D of myopia. No statistically significant difference in outcome (P = .720) was seen between the 2 groups. The cutoff points (2.0 D, 3.0 D, 4.0 D, 5.0 D, and 6.0 D) show that patients with a pre-laser SE of equal to or greater than 6.0 D of myopia had a less predictable outcome than those with a SE of less than 6.0 D of myopia (P = .026). This group had a more myopic outcome than the group with less than 6.0 D of myopia (mean SE of 0.91 ± 0.87 D versus mean SE of 0.32 ± 0.73 D, respectively). The refractive outcomes in eyes with a target of emmetropia and eyes with reading distance as a target in the previous corneal refractive laser surgery were comparable (absolute error of the mean SE 0.60 ± 0.51 D and 0.79 ± 1.03 D, respectively; P = .946, Mann-Whitney U test).. 23.

(8) Chapter 2 Cutoff Point (D). <Cutoff Point (Number of Eyes). ≥Cutoff Point (Number of Eyes). P-value. 2.0. 0.55 (8). 0.62 (66). 0.720. 3.0. 0.62 (22). 0.61 (52). 0.392. 4.0. 0.57 (42). 0.67 (32). 0.479¹. 5.0. 0.56 (58). 0.78 (16). 0.245. 6.0. 0.54 (63). 1.00 (11). 0.026*. Table 2. Comparison of outcome between eyes with different magnitudes of myopia. Absolute errors of the mean spherical equivalent postoperatively are shown. P-value of Mann Whitney test. *Statistically significant. ¹T-test.. In the case of previous LASIK, 2 flap diameters were used (8.5 mm and 9.5 mm). There was no statistically significant difference between the 2 groups in the postoperative absolute error of the mean SE (0.57 ± 0.59 D and 0.71 ± 0.34 D, respectively; P = .059, Mann-Whitney U test). The postoperative refractive outcome did not correlate with the corneal irregularity in eyes with the 3.0 mm zone and those with the 5.0 mm zone (r = 0.013 with P = .911 and r = 0.113 with P = .332, respectively). Corneal topography was categorized into oblate and prolate patterns, and there was no difference between these 2 groups in the refractive outcome (absolute error of the mean SE of 0.58 ± 0.50 D and 0.68 ± 1.06 D, respectively; P = .527, Mann-Whitney U test). Complications after IOL implantation included a macular hole in 1 eye (1.3%). This patient was excluded from the analysis. Retinal detachment without macula involvement occurred in 2 eyes (2.6%) of 1 patient with high myopia (SE 8.0 D in both eyes). The patient had vitrectomies and had no visual loss. A retinal break in the peripheral retina in 1 eye (1.3%) was successfully treated with argon laser coagulation. Intraocular lens exchange was performed in 1 eye of 1 patient (1.3%) because of a refractive surprise of 3.75 D. Laser enhancement was done after IOL implantation in 16 eyes (20.8%) because of the residual refraction. The mean time between IOL implantation and laser enhancement was 10 months (range 4 to 20 months). Neodymium:YAG (Nd:YAG) laser capsulotomy was performed in 14 eyes (18.2%) because of PCO. The mean time after IOL implantation was 14 months (range 4 to 39 months). No complications were seen after the Nd:YAG laser capsulotomy.. DISCUSSION Although the decision to implant a multifocal IOL after previous corneal refractive laser surgery is considered controversial, we decided to implant the multifocal IOL based on 24.

(9) Multifocal IOL after myopic laser surgery. the patients’ wishes to have a high degree of freedom from refractive correction, the technical feasibility, and the possibility of enhancing the outcome with a laser treatment for residual refractive errors. Patients were extensively counseled and in a process of shared decisionmaking, they concluded that the possible side effects, even the possibility of deteriorated visual quality after a refractive corneal laser procedure, was balanced by their wish for freedom from spectacles. We realize that because of the controversial nature of this decision, some surgeons would have wanted more detailed data, such as wavefront analysis and contrast sensitivity data. However, with the technology that is widely available to most cataract surgeons (ie, biometry and corneal topography), we thought our results would help the cataract surgeon make a decision about implanting a multifocal IOL after previous myopic laser surgery. Undoubtedly, the decision process could be refined with ray-tracing technology and aberrometry of the cornea, but this technology was not evaluated in this study. In this study, we evaluated the refractive and visual outcome of aspheric multifocal IOL implantation after previous corneal refractive laser surgery for myopia. To our knowledge, our cohort of 77 eyes (43 patients) is the largest reported. We found good results in terms of refraction and UDVA, with a predictability of 57% of eyes within ± 0.50 D of emmetropia and 86% of eyes within ± 1.00 D. These results are comparable to those of monofocal IOL implantation after corneal refractive laser surgery.13,14 Only a few other studies of the results of multifocal IOL implantation after myopic corneal refractive laser surgery have been reported. Muftuoglu et al.12 described a cohort of 49 eyes of 38 patients implanted with a spherical Restor multifocal IOL with a slightly higher percentage within ± 0.50 D of emmetropia (65%) and a slightly lower percentage within ± 1.00 D (84%). Fernández-Vega et al.11 compared the results of the spherical Restor IOL (22 eyes) and the aspheric Acri.LISA IOL (26 eyes) and found a predictability of 100% within ± 1.00 D of emmetropia and 86% and 85%, respectively, within ± 0.50 D after 6 months. The authors did not indicate whether these results were before or after corneal laser enhancements, and the cohort is much smaller than ours, which might partly explain the difference in outcome. In our study, 16 eyes (20.8%) had laser retreatment after IOL implantation because of a residual refraction. It is worth noting that there was a downward trend in the number of laser enhancements from the beginning to the end of our study. In the first half of the study, 28.9% (11 eyes of 39 eyes) had a laser enhancement; in the second half, the enhancement rate was 13.2% (5 eyes of 38 eyes). This decrease can be explained by the improved accuracy of the ASCRS calculator and implementation of multifocal toric IOL technology by the surgeons by the end of 2010. Before the use of multifocal toric IOLs, patients with astigmatism were offered multifocal IOLs with the stipulation that after 25. 2.

(10) Chapter 2. phacoemulsification, a laser enhancement would be necessary to treat the astigmatism. In the second half of the study, patients with astigmatism were offered a multifocal toric IOL and thus did not meet the inclusion criteria. This led to fewer laser enhancements for preexistent astigmatism. Another possible cause for the decrease in laser enhancements is that the surgical team had a clinical impression that patients who had been highly myopic had less predictable outcomes, and a selection bias in inclusion might have occurred on the assumption that the outcome might not lead to patient satisfaction. This perception was confirmed by our results showing that patients with myopia equal to or greater than 6.0 D have less predictable outcomes. In this study, 1 eye (1.3%) needed an IOL exchange because of a refractive surprise. This patient had multiple corneal refractive laser surgeries because she could not adapt to monovision; this was tested extensively preoperatively. We assume that the multiple laser procedures made the IOL calculation inaccurate and caused the refractive surprise. Posterior capsule opacification is 1 of the most common complications after cataract surgery.15 It is known that Nd:YAG laser capsulotomy rates are higher with multifocal IOLs than with monofocal IOLs and that the capsulotomies are performed earlier.16,17 We had a relatively low Nd:YAG capsulotomy rate (18.2%, 14 eyes). The mean time between IOL implantation and Nd:YAG laser capsulotomy was 14 months (range 4 to 39 months). One explanation could be the shorter follow-up time in our cohort because it is known that PCO might increase markedly after a few years.18 Also, we had studied the influence of Nd:YAG laser capsulotomy on refraction previously and found that a small number of cases showed a small refractive change after the Nd:YAG laser capsulotomy.19 This might have made us cautious, performing Nd:YAG laser capsulotomies only when the visual acuity was significantly diminished or patients had severe visual complaints. It is known that multifocal IOL implantation achieves its best results as a bilateral procedure.20 In this study, 9 unilateral eyes were included because the other eye had a hyperopic laser treatment (4 eyes), no previous corneal laser surgery (3 eyes), amblyopia (1 eye), or a postoperative macular hole (1 eye). The limitation of this study was the use of retrospective data. We did not address the outcome measures of satisfaction, photopic side effects, and spectacle independence. These aspects warrant more attention. In conclusion, apodized diffractive multifocal IOL implantation after corneal refractive laser surgery for myopia provided good visual acuity and refraction results. A limited number of patients needed a laser enhancement for residual refraction. The results were less predictable with myopia greater than 6.0 D.. 26.

(11) Multifocal IOL after myopic laser surgery. WHAT WAS KNOWN - Intraocular lens calculation after previous corneal refractive laser surgery is less accurate because of the inaccurate determination of the corneal curvature and the inaccurate estimation of the effective lens position. - Multifocal IOL implantation after previous corneal refractive laser surgery for myopia is controversial because of the assumption that the laser treatment affects the cornea in such a manner that multifocal IOL implantation could cause deterioration in vision.. WHAT THIS PAPER ADDS - With the current IOL calculation methods, multifocal IOL implantation after previous corneal refractive laser surgery for myopia provided good visual acuity and refraction results. - Results were less predictable in eyes with myopia greater than 6.0 D.. 27. 2.

(12) Chapter 2. REFERENCES 1. . Solomon KD, Fernández de Castro LE, Sandoval HP, Biber JM, Groat B, Neff KD, Ying MS, French JW, Donnenfeld ED, Lindstrom RL, for the Joint LASIK Study Task Force. LASIK world literature review; quality of life and patient satisfaction. Ophthalmology 2009; 116:691–701 2. Yoshino M, Bissen-Miyajima H, Minami K, Taira Y. Five-year postoperative outcomes of apodized diffractive multifocal intraocular lens implantation. Jpn J Ophthalmol 2013; 57:510–513 3. van der Linden JW, van der Meulen IJ, Mourits MP, Lapid-Gortzak R. Comparison of a hydro philic and a hydrophobic apodized diffractive multifocal intraocular lens. Int Ophthalmol 2013; 33:493–500 4. de Vries NE, Webers CAB, Montés-Micó R, Tahzib NG, Cheng YYY, de Brabander J, Hendrikse F, Nuijts RMMA. Long-term follow-up of a multifocal apodized diffractive intraocular lens after cataract surgery. J Cataract Refract Surg 2008; 34:1476–1482 5. Rosen E, Alió JL, Dick HB, Dell S, Slade S. Efficacy and safety of multifocal intraocular lenses following cataract and refractive lens exchange: metaanalysis of peer-reviewed publica tions. J Cataract Refract Surg 2016; 42:310–328 6. Braga-Mele R, Chang D, Dewey S, Foster G, Henderson BA, Hill W, Hoffman R, Little B, Mamalis N, Oetting T, Serafano D, Talley-Rostov A, Vasavada A, Yoo S, for the ASCRS Cata ract Clinical Committee. Multifocal intraocular lenses: relative indications and contraindi cations for implantation. J Cataract Refract Surg 2014; 40:313–322 7. Seitz B, Langenbucher A, Nguyen NX, Kus MM, Küchle M. Underestimation of intraocular lens power for cataract surgery after myopic photorefractive keratectomy. Ophthalmology 1999; 106:693–702 8. Chan TCY, Liu D, Yu M, Jhanji V. Longitudinal evaluation of posterior corneal elevation after laser refractive surgery using swept-source optical coherence tomography. Ophthalmology 2015; 122:687–692 9. Wang L, Hill WE, Koch DD. Evaluation of intraocular lens power prediction methods using the American Society of Cataract and Refractive Surgeons post-keratorefractive intraocular lens power calculator. J Cataract Refract Surg 2010; 36:1466–1473 10. Khor WB, Afshari NA. The role of presbyopia-correcting intraocular lenses after laser in situ keratomileusis. Curr Opin Ophthalmol 2013; 24:35-40 11. Fernández-Vega L, Madrid-Costa D, Alfonso JF, Montés-Micó R, Poo-López A. Optical and visual performance of diffractive intraocular lens implantation after myopic laser in situ keratomileusis. J Cataract Refract Surg 2009; 35:825-832 12. Muftuoglu O, Dao L, Mootha VV, Verity SM, Bowman RW, Cavanagh HD, McCulley JP. Apodized diffractive intraocular lens implantation after laser in situ keratomileusis with or without subsequent excimer laser enhancement. J Cataract Refract Surg 2010; 36:1815–1821 13. Abulafia A, Hill WE, Koch DD, Wang L, Barrett GD. Accuracy of the Barrett True-K formula for intraocular lens power prediction after laser in situ keratomileusis or photorefractive keratectomy for myopia. J Cataract Refract Surg 2016; 42:363–369. 28.

(13) Multifocal IOL after myopic laser surgery 14. Wang L, Tang M, Huang D, Weikert MP, Koch DD. Comparison of newer intraocular lens power calculation methods for eyes after corneal refractive surgery. Ophthalmology 2015; 122:2443–2449. 15. Schaumberg DA, Dana MR, Christen WG, Glynn RJ. A systematic overview of the incidence of posterior capsule opacification. Ophthalmology 1998; 105:1213–1221 16. Biber JM, Sandoval HP, Trivedi RH, Fernández de Castro LE, French JW, Solomon KD. Comparison of the incidence and visual significance of posterior capsule opacification between multifocal spherical, monofocal spherical, and monofocal aspheric intraocular lenses. J Cataract Refract Surg 2009; 35:1234–1238 17. Shah VC, Russo C, Cannon R, Davidson R, Taravella MJ. Incidence of Nd:YAG capsulot omy after implantation of AcrySof multifocal and monofocal intraocular lenses: a case controlled study. J Refract Surg 2010; 26:565–568 18. Lundqvist B, Mönestam E. Ten-year longitudinal visual function and Nd: YAG laser capsu lotomy rates in patients less than 65 years at cataract surgery. Am J Ophthalmol 2010; 149:238–244 19. Vrijman V, van der Linden JW, Nieuwendaal CP, van der Meulen IJE, Mourits MP, LapidGortzak R. Effect of Nd:YAG laser capsulotomy on refraction in multifocal apodized diffrac tive pseudophakia. J Refract Surg 2012; 28:545–550 20. Cionni RJ, Osher RH, Snyder ME, Nordlund ML. Visual outcome comparison of unilateral versus bilateral implantation of apodized diffractive multifocal intraocular lenses after cataract extraction; prospective 6-month study. J Cataract Refract Surg 2009; 35:1033– 1039. OTHER CITED MATERIAL A. Nederlands Gezelschap Voor Refractie Chirugie. Consensus Refractiechirurgie; Februari 2006 Herzien: Juli 2009 en Juni 2013. Auteurs versie Februari 2006: Aalders-Deenstra V, Beerthuizen J, Bolmers PJD, den Boon JM, Braakman R, Crobach PSJR, Eggink CA, Geerards AJM, Kraaijenga AD, Luger M, Luyten GPM, Odenthal M, Rijneveld A, van Rooij, Rouwen APJ, van Tilburg CJG, Tutein Nolthenius P, Trap NH, Verdoorn C. Aanvullingen herziene versie juli 2009 door: Bartels M, Beerthuizen J, Copper M, Landesz M, Lapid R, Van Nouhuijs H, Nuyts R, Wolter O, Van Rooy J, Trap N. Aanvullingen herziene versie juni 2013: Beerthuizen J, Eggink C, Lapid R, Luger M, van Nouhuijs H, vd Pol R, Rademakers J, Trap N. Available at: http://www .oogheelkunde.org/sites/www.oogheelkunde.org/files/richtlijnen/Consensus RC2013.pdf. Accessed May 6, 2017. 29. 2.

(14) Chapter 2. AUTHOR CONTRIBUTIONS Violette Vrijman contributed to the study concept and design, data acquisition, data analysis and interpretation, writing the manuscript and producing the final manuscript Jan Willem van der Linden contributed to the data acquisition, data interpretation and critical revision of the manuscript. Ivanka J.E. van der Meulen contributed to the data acquisition, data interpretation and critical revision of the manuscript. Maarten P. Mourits contributed to the data interpretation and critical revision of the manuscript. Ruth Lapid-Gortzak contributed to the study concept and design, data acquisition, data interpretation, writing the manuscript, critical revision of the manuscript and submission of the final manuscript. 30.

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