Refractive lens exchange with distance-dominant diffractive bifocal intraocular lens implantation

Transcription

1 Graefes Arch Clin Exp Ophthalmol (2010) 248: DOI /s REFRACTIVE SURGERY Refractive lens exchange with distance-dominant diffractive bifocal intraocular lens implantation José F. Alfonso & Luis Fernández-Vega & Susana Ortí & Robert Montés-Micó Received: 17 January 2010 / Accepted: 15 February 2010 / Published online: 16 March 2010 # Springer-Verlag 2010 Abstract Purpose To assess efficacy, safety and predictability after refractive lens exchange (RLE) in patients who had bilateral implantation of a distance-dominant diffractive bifocal intraocular lens (IOL). Methods Seventeen patients (34 eyes) were examined after RLE with bilateral implantation of a diffractive bifocal 447D IOL. Eyes were divided into myopic and hyperopic groups. Monocular uncorrected distance visual acuity, best-corrected distance visual acuity (BCVA), uncorrected distance near visual acuity, and best distance-corrected near visual acuity (BCNVA) were recorded preoperatively and 6 months after surgery. Results Efficacy indexes were 1.10 for myopic and 0.98 for hyperopic eyes, at 6 months postoperatively. No eye lost 1 line of BCVA. For the myopic group, four eyes gained 1 line, and six eyes gained 2 lines; for the hyperopic group, three eyes gained 1 line, and five eyes gained 2lines.Safety indexes were 1.21 and 1.08 for myopic and hyperopic eyes The authors have no proprietary interest in any of the materials mentioned in this article. J. F. Alfonso (*) : L. Fernández-Vega Fernández-Vega Ophthalmological Institute, Avda. Dres. Fernández-Vega 34, Oviedo, Spain j.alfonso@fernandez-vega.com J. F. Alfonso : L. Fernández-Vega Surgery Department, School of Medicine, University of Oviedo, Oviedo, Spain S. Ortí : R. Montés-Micó Optics Department, Faculty of Physics, University of Valencia, Valencia, Spain respectively. No eye lost 1 line of BCNVA. Safety indexes at near were 1.02 for myopic and 1.01 for hyperopic eyes. Efficacy indexes at near were 1.02 for myopic and 1.00 for hyperopic eyes. Conclusions Six-month results of bilateral implantation of a distance-dominant diffractive bifocal IOL for RLE demonstrated efficacy, safety, and predictability in correcting ametropia and presbyopia. Keywords Refractive lens exchange. Bifocal IOL. Diffractive. Visual acuity Introduction In cataract and non-cataract patients, the wish is growing to reduce or eliminate their dependence on spectacles or contact lens. Currently, there are several options for treating the refractive surgery patients; however, the limitations in laser refractive surgery (extreme degrees of myopia, hyperopia and astigmatism) have increased the implant of intraocular lenses (IOLs) for the correction of refractive errors. Additionally, in presbyopic patients the demand is higher, since it is necessary to provide pseudoacommodation [1, 2]. The improvement in the results of cataract surgery, such as new phacoemulsification and IOL technology (multifocal and accommodative IOL) to maximize the results of postoperative refraction, has made possible improvement in the results obtained through this technique, and the use of lens surgery as a refractive modality in patients without cataracts has increased in popularity, which is described as clear lens extraction or refractive lens exchange (RLE). In addition to providing correction of ametropia and presbyopia, it is possible to eliminate the need for cataract surgery in the future. When accurate biometry and lens power calculations is

2 1508 Graefes Arch Clin Exp Ophthalmol (2010) 248: performed, it is possible to maximize the success with this procedure [2 4]. In contrast to monofocal IOLs, introduction of multifocal IOLs aims to provide good distance and near vision after cataracts or RLE surgery, creating a minimum of two images on the retina. The overlap of the in-focus and out-of-focus image can produce a decrease in contrast sensitivity and photic phenomena such as glare and halo, especially at night [3, 4]. To reduce these effects, different light distribution between foci has been proposed [4 7]. The 447D IOL provides 70% of the available light energy for distance vision in the dominant eye, leaving 30% of the available energy for near focus. Clinical studies have demonstrated good visual outcomes after RLE and multifocal IOL implantation [8 14]. However, to our knowledge, no study has assessed the visual performance of these IOLs after RLE. The objective of this study was to evaluate efficacy, safety and predictability after RLE in a sample of patients who had symmetric bilateral implantation of a distance-dominant diffractive bifocal 447D IOL. Patients and methods Thirty-four eyes of 17 consecutive patients were included in a prospective study, who underwent bilateral implantation of a distance-dominant diffractive bifocal 447D IOL at the Fernández-Vega Ophthalmological Institute, Oviedo, Spain. Inclusion criteria were age between 35 and 70 years and the desire not to wear any form of spectacle or contact lens correction for distance and near vision. The exclusion criteria included cataract, best-corrected distance visual acuity (BCVA) < 20/25 in either eye, preoperative astigmatism > 1.50 diopters (D), history of glaucoma or retinal detachment (RD), corneal disease, previous corneal or intraocular surgery, abnormal iris, pupil deformation, macular degeneration or retinopathy, neuro-ophthalmic diseases, and history of ocular inflammation. Before the RLE procedure, patients had a complete ophthalmologic examination, including manifest and cycloplegic refraction, keratometry, slit-lamp biomicroscopy, Goldmann applanation tonometry, and binocular indirect ophthalmoscopy through dilated pupils. Axial length and anterior segment size were measured with the Zeiss Humphrey IOL Master biometer (Carl Zeiss Meditec, Inc., Dublin, CA, USA). The SRK/T formula was used in myopic eyes. The Holladay II formula was used for IOL power calculation in hyperopic eyes. The targeted refraction was emmetropia. All surgeries in this study were operated by phacoemulsification with the Infiniti Vision System (Alcon, Fort Worth, TX, USA) using topical anesthesia and a clear corneal 2.8 to 3.2-mm incision by two experienced surgeons (JFA, LF-V). Phacoemulsification was followed by irrigation and aspiration of the cortex and IOL implantation in the capsular bag. RLE was performed in both eyes within 2 weeks. There were no complications in any of the cases. The tenets of the Declaration of Helsinki were followed in this research. Informed consent was obtained from all patients after the nature and possible consequences of the study were explained. Institutional review board approval was obtained. All patients had symmetric bilateral implantation of the 447D IOL. This bifocal diffractive single-piece IOL has a 6.0 mm foldable acrylate aspherical optic and an overalldiameterof11.0mm.lenspowervariedfrom0.0 diopter (D) to D, incorporating a +4.0 D near addition (add) power. The 447D IOL has a 70% to 30% light distribution between the distance and near foci. Bilateral implantation may result in better binocular visual performance at distance and near focus; with one eye compensating for the other at its stronger focus [15]. The optical principle of diffraction used here creates two focal points or two foci. When light passes through a narrow slit or opening or edge, it slows down and its direction changes slightly. Depending on the relative phases of the two wave fronts, the light waves can either be constructive or reinforcing one another (strengthening of light) or they can be destructive or weakening one another (weakening of the light). Traditional diffractive IOLs feature concentric rings covering either anterior or posterior surface which are differentiated from each other by a step height of about 2 μm. These diffractive IOLs allow the creation of the two foci, and can be made totally independent of pupil. However, some patients implanted with these IOLs may experience the perception of halos and glare at night [6, 7, 16]. Patients were scheduled for clinical evaluation preoperatively and 1 day, 1 week, and 1, 3, and 6 months postoperatively. Standard ophthalmologic examinations, including manifest refraction, slit-lamp biomicroscopy, Goldmann applanation tonometry, and binocular indirect ophthalmoscopy, were performed at all visits. Tilt and centration of the IOLs in relation to the visual axis were assessed using Scheimpflug videophotography (EAS-1000, Nidek). Visual acuity measurements were done using the Snellen decimal scale. Monocular uncorrected distance visual acuity (UCVA), BCVA, uncorrected near visual acuity (UCNVA), and best distance-corrected near VA (BCNVA) were recorded preoperatively and postoperatively at 6 m and 33 cm respectively in all patients. Near distance was selected considering that the add power of the IOL is D, corresponding to approximately 3.2 D in the spectacle plane. All examinations were performed 6 months after IOL

3 Graefes Arch Clin Exp Ophthalmol (2010) 248: implantation by the same ophthalmic technician, who was unaware of the study s objective. Data analysis was performed using SPSS for Windows (version 12.0, SPSS, Inc.). Normality was checked by the Shapiro Wilk test, and the t-test was performed to compare differences in visual acuity. Differences were considered statistically significant when the P value was less than 0.01 (i.e., at the 1% level). Results Thirty-four patients, with mean age 52.90±6.81 years (range from 35 to 61 years) and mean axial length 23.82± 3.63 mm (range from to mm), were included in this study. Patient demographics are shown in Table 1. A total of 34 eyes received a distance dominant diffractive bifocal 447D IOL. Eyes were divided into the myopic group (n=14), with an average preoperative spherical equivalent (SE) refraction of 10.36±4.03 D, and the hyperopic group (n=20), with an average preoperative SE refraction of +4.87±1.68 D. With respect to safety, we obtained in the myopic group, 6 months after surgery, the following results: four eyes did not change after surgery, four eyes gained 1 line, two eyes gained two lines, and four eyes gained more than 2 lines of visual acuity (Fig. 1). The safety index (ratio of postoperative and preoperative BCVA) at 6 months was For the hyperopic group, twelve eyes had an unchanged BCVA after surgery, three eyes gained 1 line, and five eyes gained two lines of visual acuity. The safety index at 6 months was If we evaluated efficacy, we found that in the myopic group 6 months postoperatively mean UCVA was 0.90± Fig. 1 Changes in best spectacle-corrected distance visual acuity (BCVA) 6 months after refractive lens exchange with distancedominant diffractive bifocal 447D intraocular lens implantation in both groups (safety) BCVA changed from 0.82±0.16 preoperatively to 0.99±0.03 at 6 months (P<0.001) (Fig. 2). The overall efficacy index (mean postoperative UCVA/mean preoperative BCVA) at 6 months was In the hyperopic group, 6 months postoperatively, mean UCVA was 0.88±0.18. BCVA changed from 0.89±0.11 preoperatively to 0.96± 0.09 at 6 months (P>0.1). The efficacy index at 6 months was The deviation of the achieved SE refraction from the calculated SE refraction was calculated (predictability). After 6 months, 14 eyes (100%) and 20 eyes (100%) of the myopic and hyperopic groups were within ± 1.00D of the desired refraction (Fig. 3). Twelve eyes (85.71%) for the myopic group and 18 eyes (90%) for the hyperopic group were within±0.50 D of the target refractive change. The mean postoperative SE for the myopic and hyperopic groups was ±0.31 D and +0.04±0.27 D respectively, at 6 months. Table 1 Demographic characteristics of participants Hyperopic Myopic D = dioptres; IOL = intraocular lens; SD = standard deviation No. of eyes Age (years) ± SD 52.45±7.04 (range 35 61) 53.36±4.27 (range 46 59) Gender (male/female) 6/14 0/14 IOL power (D) ± SD 28.32±2.43 (range 25 34) 8.53±4.23 (range 0 16) Preoperative sphere (D) ± SD 5.22±1.76 (range ) -9.91±4.07 (range -4 to -19) Preoperative cylinder (D) ± SD -0.70±0.47 (range to 0) -0.89±0.37 (-0.50 to -1.50) Postoperative sphere (D) ± SD 0.14±0.35 (range to 1) -0.09±0.32 (-0.50 to 0.50) Postoperative cylinder (D) ± SD -0.18±0.24 (range-0.50 to 0) -0.29±0.24 (range to 0) Mean preoperative keratometry (K) (D) ± SD K ± ±1.31 K ± ±1.45 Range of preoperative K (D) Mean axial length (mm) ± SD 21.15± ±1.51 Range of axial length (mm)

4 1510 Graefes Arch Clin Exp Ophthalmol (2010) 248: Fig. 2 Uncorrected distance visual acuity (UCVA) and best spectaclecorrected distance visual acuity (BCVA) over the follow-up period in both groups after refractive lens exchange with asymmetric distancedominant diffractive bifocal 447D intraocular lenses implantation (efficacy) Safety and efficacy at near vision are depicted in Figs. 4 and 5 respectively. In the myopic group, 6 months after surgery, none of the examined eyes had lost 1 line of BCNVA (Fig. 4), 11 eyes did not change after surgery, and three eyes gained 1 line of visual acuity. The safety index (ratio of postoperative and preoperative BCNVA) at 6 months was BCNVA was maintained at a similar level after the surgery, changed from 0.98±0.04 preoperatively to 1.00±0.00 at 6 months (Fig. 5). The efficacy index (mean postoperative UCNVA/mean preoperative BCNVA) at 6 months was For the hyperopic group, 18 eyes had an unchanged BCNVA and two eyes gained 1 line of visual acuity. The safety index at 6 months was Six months postoperatively, mean UCNVA was 0.98±0.07. The efficacy index at 6 months was No eye required a secondary intervention postoperatively, no potentially sight-threatening complications were observed, and no eye was in the need of neodymium:yttrium-garnet (Nd: YAG) capsulotomy up to the postoperative last visit. Discussion When the crystalline lens is removed and subsequently replaced with an IOL this is known as RLE. As several studies [8 15, 17 20] have shown this procedure can lead to an effective, safe, predictable, and stable outcome with a low risk of complications. In addition, stereoacuity before and after RLE and multifocal IOL implantation has recently has been evaluated, and it has been found that stereoacuity was unchanged after RLE [21]. Limitations in corneal surgery have led to a resurgence of RLE for patients with prescriptions outside the limits of corneal refractive procedures, in addition to patients with routine refractive Fig. 3 Attempted versus achieved correction (predictability) 6 months after refractive lens exchange with distance-dominant diffractive bifocal 447D intraocular lenses implantation for myopic (R=0.99) and hyperopic (R=0.99) patients. D = diopters errors requesting a surgical procedure to achieve emmetropia and also address presbyopia [22, 23]. Multifocal IOLs (diffractive and refractive) aim to correct both distance and near vision, providing pseudoaccommodation after lens removal, creating two separate focal points along the optical axis. The correct keratometry and anterior chamber depth and axial length measurement should be performed as accurately as possible, to ensure the accurate calculation of IOL power and success of pseudoaccommodative IOL implantation [24, 25]. IOL power selection in patients with high ametropia should be performed carefully, because axial length is difficult to measure. Unlike what happens with hyperopia, myopia results from having an eye refractive power over its axial length. This may be due either to the eyes having high axial

5 Graefes Arch Clin Exp Ophthalmol (2010) 248: Fig. 4 Changes in best spectacle-corrected near visual acuity (BCNVA) 6 months after refractive lens exchange with distance dominant diffractive bifocal 447D intraocular lenses implantation in both groups (safety) length or to an increase in dioptric power from one or more elements of refraction [26]. In our study, we used the SRK/T formula for myopic eyes, because it has been shown to be accurate in eyes with greater axial length [24]. For hyperopic eyes, the Holladay II formula was used, on the basis that for short eyes (about 22.0 mm) it performs better than the SRK/T formula [25]. Using these formulae for IOL power calculation in each group, minimal deviation from target refraction was obtained (residual hyperopia between and D after multifocal IOL implantation has been suggested to avoid halos, preserving distance and near vision). Our IOL power choice after considering both formulae was accurate enough to achieve a mean postoperative SE of about <0.25 D of the targeted refraction (-0.23±0.31 and+0.04±0.27 D for myopic and hyperopic groups respectively). Fig. 5 Uncorrected near visual acuity (UCNVA) and best spectaclecorrected near visual acuity (BCNVA) over the follow-up period in both groups after refractive lens exchange with distance-dominant diffractive bifocal 447D intraocular lenses implantation (efficacy) Through multifocal IOLs, it is possible to achieve emmetropia, both for distance and near, especially if there is a accurate biometry, and plan the surgery in relation to the criteria of indication of the multifocal lens suitable for the real needs of each patient (both in cataract patients and in patients after RLE). Previous studies have documented the efficacy of multifocal IOLs [2, 6, 27 29], and other studies have reported that bilateral implantation may result in better binocular visual outcomes [15]. Contrast sensitivity function is reduced in different ways depending on the IOL design [2, 6, 9]. The main advantage of the diffractive IOLs over refractive IOLs is that they are less pupil-dependent; however, they can induce slight night-vision disturbances and a reduction in contrast sensitivity [6, 9, 30]. We assessed efficacy, safety and predictability after RLE in myopic and hyperopic eyes after symmetric bilateral implantation of a distance-dominant diffractive bifocal 447D IOL, and obtained high safety and efficacy indexes at distance and near in both groups. However, at distance the myopic group achieved better visual outcomes. Safety and efficacy indexes were 1.21 and 1.10 for myopic eyes, but in the hyperopic group were 1.08 and Unlike for near vision, values were similar in both groups; safety and efficacy indexes were 1.02 for myopic eyes, and were 1.01 and 1 for hyperopic eyes. Note also that postoperative differences were only statistically significant for the value of UCVA (P< 0.001). No eyes lost any line of BCVA at follow-up. In the myopic group, 28.57% of all eyes had no change in their BCVA, and 60 % had no change in the hyperopic group. in the myopic and hyperopic groups respectively, 71.43% and 40% of eyes gained 1 or more lines of BCVA. Comparing the two groups, myopic eyes gained more lines of BCVA than hyperopic eyes. This difference can be explained by magnification and minimization of the retinal image in myopic and hyperopic eyes respectively. UCVA at 6 months was about 0.90 in both groups. BCVA was 0.99 for myopic eyes and 0.96 for hyperopic eyes. Predictability was also good, with 14 eyes (100%) and 20 eyes (100%) of the myopic and hyperopic groups within ± 1.00D of the desired refraction. Twelve eyes (85.71%) for the myopic group and 18 eyes (90%) for the hyperopic group were within ± 0.50 D of the target refractive change. At 6 months, all eyes obtained low postoperative SE values 0.23±0.31 and ±0.27 D for myopic and hyperopic eyes respectively. At near vision, 78.57% and 90% of the eyes remained unchanged in their BCNVA, for myopes and hyperopes respectively, and the rest gained 1 line of BCNVA. BCNVA was maintained at a similar level after surgery in both groups (close to 1.00). Although visual outcomes have never been studied after RLE in patients who had bilateral implantation of

6 1512 Graefes Arch Clin Exp Ophthalmol (2010) 248: symmetric distance-dominant diffractive bifocal 447D IOL, many studies [8 14, 17 21] have evaluated this technique with other multifocal IOLs: Array refractive IOL, Tecnis diffractive IOL, and AcrySof ReSTOR diffractive IOL. And previous studies have reported good visual outcomes in patients implanted with IOLs used in this study, but after cataract surgery [31]. Goes [18] assessed visual outcomes and patient satisfaction after RLE with bilateral implantation of multifocal Tecnis IOL, and reported that these IOLs provided good distance and near vision after RLE, and the majority of patients (92.8%) were totally free from spectacles. Dick et al. [14] and Packer et al. [13] evaluated safety and efficacy after RLE and Array multifocal IOL implantation, and reported that RLE was a safe and effective refractive surgery modality in presbyopic patients. Most articles that evaluate the results of RLE after multifocal IOL implantation were using the AcrySof ReSTOR multifocal IOL. Among these studies, Montés-Micó et al. [9] examined the optical quality of 30 healthy presbyopic eyes after RLE and implantation of AcrySof ReSTOR multifocal IOL, and reported that safety and efficacy indexes were 1.01 and 0.96 at distance, and 1.07 and 1.06 at near. UCVA postoperatively at distance and near was comparable to preoperative BCVA. In another study, Fernández-Vega et al. [8] assessed 112 patients (divided into myopic and hyperopic groups) after RLE with bilateral implantation of AcrySof ReSTOR multifocal IOL, and obtained VA was 20/25 or better in 100% of the eyes; efficacy indexes at distance were 0.97 and 0.96 for myopic and hyperopic patients respectively, and safety indexes were 1.05 and 1.02 respectively. At near, both indexes were higher for hyperopic group. Ferrer-Blasco et al. [32] examined 30 hyperopic eyes after RLE and AcrySof ReSTOR IOL implantation, and reported that safety and efficacy indexes were 1.02 and 0.91 for distance, and 1.04 and 1.02 for near. Contrast sensitivity was also good at distance and near. Several previous studies have evaluated the performance of asymmetric multifocal IOLs implantation (two bifocal diffractive IOLs with different light distribution between the two foci: the Acri.Tec 733D IOL has a 30% to 70% light distribution between the distance focus and near focus, and 737D IOL, implanted in the dominant eye, has a 70% to 30% light distribution between the distance focus and near focus). Jacobi et al. [5] developed this new concept, asymmetrical bilateral multifocal IOL implantation to enhance visual performance of the multifocal IOL after binocular implantation. Alfonso et al. [7] assessed the quality of vision in 343 patients who had implantation of asymmetric Acri.Twin bifocal diffractive IOLs, and reported that BCVA and BCNVA were 0.031±0.059 and 0.005±0.024 respectively. Similarly, Schmidinger et al. [33] evaluated the same system in 16 patients, and obtained a BCVA of ±0.007 and a BCNVA of 0.003± There are several previous studies that assessed the visual outcomes after symmetric bilateral implantation of the diffractive bifocal 447D IOL in cataract patients. Fernández-Vega et al. [31] analyzed 50 patients who had bilateral implantation of a distance-dominant diffractive bifocal 447D IOL, and reported that this IOL provided good simultaneous distance and near vision; BCVA and BCNVA were 0.02±0.04 logmar and 0.04±0.03 logmar respectively. They also concluded that their results were slightly better for distance and worse for near vision than those reported in previous studies of the asymmetric Acri. Twin system. After evaluating the previous studies, we can confirm that the results obtained in the present study are comparable to those in previous reports. Safety and efficacy indexes obtained in the present study were slightly better than obtained after RLE and AcrySof ReSTOR implantation. And also, although this is not a comparative study of symmetric and asymmetric implantation, through symmetric implantation we can avoid the problems associated with the choice of the dominant eye [34, 35] and this may solve binocular vision intolerance reported by some patients to different light distribution between eyes [7], which achieved equally good visual outcomes. In moderate and high myopes, RLE may raise concerns about significant complications, especially RD. For eyes with long axial length, the greater the vitreoretinal stretching. Extracting the crystalline lens increases the risk for posterior vitreous detachment, which seems to be the major causative factor in retinal breaks, which in turn lead to RD [36, 37]. Modern techniques of extracapsular cataract extraction have lowered, but not eliminated, the risk of late RD. Fernández- Vega et al. [19] reported that the overall incidence of RD was 2.1% for 190 eyes (minimum axial length of mm) undergoing RLE. Colin et al. [37] have reported a incidence of RD of 8.1% after 7 years in 49 high myopic eyes (> 12 D) undergoing RLE. When it is considered as a hyperopic treatment, some of the disadvantages associated with this procedure as a treatment for myopia are not as relevant. Previous studies [20] on RLE for hyperopia demonstrate that this is a safe and effective procedure. The increased risk of an RD after RLE surgery is less relevant in these patients. When the axial length is low, hyperopic eyes are predisposed to choroidal effusions, and glaucoma is always a potential problem associated with IOL implantation in small eyes [31]. Moreover, in some cases it is necessary to implant more than one IOL (piggyback IOLs) to correct for hyperopia after RLE [38]. Other potential risks of RLE surgery with IOL implants include the risks associated with any cataract surgery (RD, cystoids, macular edema, hemorrhage, and endophthalmitis). Lyle et al. [17]

7 Graefes Arch Clin Exp Ophthalmol (2010) 248: assessed the results of RLE and IOL implantation in 31 eyes with high myopia and six eyes with high hyperopia, and the results showed that during the 20-month mean follow-up, posterior capsule opacification was the major complication and it developed faster than reported in other studies, but no RD or cystoid macular edema was observed. Leysen et al. [39] reported indications, surgical complications, and outcomes of IOL exchange procedures performed over 5 years and to correlate the incidence of perioperative anterior vitrectomy in eyes previously treated by Nd:YAG laser capsulotomy, and the results showed that decentration of pseudoaccommodating IOLs accounted for 14% of all IOL exchanges. Vitreous loss necessitating anterior vitrectomy was strongly correlated with preoperative Nd:YAG laser capsulotomy. In conclusion, RLE with symmetric bilateral implantation of a distance-dominant diffractive bifocal 447D IOL is an effective procedure for correcting ametropia and presbyopia. However, comparing the two groups, myopic eyes gained more lines of BCVA than hyperopic eyes. In addition, safety and efficacy indexes were greater for the myopic group. Safety and efficacy at near vision were at same levels in both groups. The changes affecting the retinal image, magnification and minimization in myopic and hyperopic patients respectively could explain these differences. Considering our results, symmetric bilateral implantation offers greater advantages than the asymmetric, and is indicated for RLE and cataract surgery, except in cases with marked ocular dominance. Future investigations of visual performance after implantation of the asymmetric bilateral Acri.Twin bifocal IOL should include large samples, evaluation of contrast sensitivity, pupil diameter in photopic and mesopic conditions, intermediate visual acuity, and quality of vision questionnaire. Acknowledgement This research was supported in part by a Ministerio de Ciencia e Innovación Research Grants to Robert Montés-Micó (#SAF # and #SAF #). References 1. Alfonso JF, Montés-Micó R (2008) RLE with multifocal IOLs. Bioptics approach. In: Chang DF (ed) Mastering refractive IOLs. The art and science. SLACK, Thorofare, NJ, USA, pp Chun MW, Kageyama JY, Barnhart Fox L, Weissman BA (2006) Patients with high refractive error. In: Benjamin WJ (ed) Borish s. Clinical refraction. Butterworth Heinemann Elsevier, St. Louis, pp Fine IH, Hoffman RS, Packer M (2003) Refractive lens exchange with a multifocal intraocular lens. In: Tsubota K, Boxer Wachler BS, Azar DT, Koch DD (eds) Hyperopia and presbyopia. Marcel Dekker, New York, pp Bissen-Miyajima H (2003) Multifocal IOLs for presbyopia. In: Tsubota K, Boxer Wachler BS, Azar DT, Koch DD (eds) Hyperopia and presbyopia. Marcel Dekker, New York, pp Jacobi FK, Kammann J, Jacobi WK, Grosskopf U, Walden K (1999) Bilateral implantation of asymmetrical diffractive multifocal intraocular lenses. Arch Ophthalmol 117: Schmidinger G, Geitzenauer W, Hahsle B, Klemen UM, Skorpik C, Pieh S (2006) Depth of focus in eyes with diffractive bifocal and refractive multifocal intraocular lenses. J Cataract Refract Surg 32: Alfonso JF, Fernández-Vega L, Señaris A, Montés-Micó R (2007) Quality of vision with the Acri.Twin asymmetric diffractive bifocal intraocular lens system. J Cataract Refract Surg 33: Fernández-Vega L, Alfonso JL, Rodríguez PP, Montés-Micó R (2007) Clear lens extraction with multifocal apodized diffractive intraocular lens implantation. 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