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Wavefront Aberrations in Eyes with Acrysof Monofocal Intraocular Lenses

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Wavefront Aberrations in Eyes with Acrysof Monofocal Intraocular Lenses Wavefront Aberrations in Eyes With Acrysof Monofocal Intraocular Lenses Prema Padmanabhan, MS; Geunyoung Yoon, PhD; Jason Porter, PhD; Srinivas K. Rao, FRCSEd; Roy J, MSc; Mitalee Choudhury, BS ABSTRACT hacoemulsifi cation, with the implantation of a fold- able intraocular lens (IOL), has become the most 1 PURPOSE: To characterize and measure the ocular ab- P popular technique for cataract surgery. The small errations in eyes implanted with monofocal intraocular self-sealing incision has reduced surgically induced astig- lenses (IOLs) and to study any correlation between post- matism.2 The continuous curvilinear capsulorrhexis has in- operative aberrations and surgical factors. creased the surgeon’s ability to ensure a stable centration of the IOL. Precision in biometry and improvements in calcula- METHODS: A Tscherning aberroscope was used to mea- tion of IOL power have enhanced the predictability of desired sure the wavefront aberrations of 62 eyes that had un- dergone phacoemulsifi cation with the implantation of postoperative results. All of these optical and biomechanical foldable monofocal Acrysof MA60BM IOLs (Alcon Labora- factors are responsible for the qualifi cation of cataract surgery tories Inc, Ft Worth, Tex). The Zernike coeffi cients, mea- as a “refractive procedure.” sured with a pupil diameter of 6 mm, were compared Until recently, the term “refractive procedure” has been with those of a normal dataset of 82 eyes of healthy used solely for spherocylindrical corrections. We now know young myopes. that optical imperfections other than spherocylindrical re- 3-5 0 fractive errors infl uence visual function. The introduction RESULTS: Spherical aberration (Z4) was the most pre- dominant higher order aberration, with a mean value of wavefront sensors into clinical practice has given the cli- of 0.37Ϯ0.16 µm. A statistically signifi cant linear re- nician a powerful tool to measure and examine these aber- lationship was noted between the magnitude of post- rations and thereby describe retinal image quality in more operative spherical aberration and the dioptric power of defi nitive terms.6 the IOL. The mean spherical aberration was 33 times more in the pseudophakic group than in normal young Most IOLs marketed today have better optical quality than 7-10 myopic eyes. The other major higher order aberrations that of a healthy crystalline lens. However, inserting IOLs -3 Ϫ Ϯ were trefoil (Z 3) with a mean of 0.13 0.22 µm and of better optical quality does not directly translate to having -1 Ϫ Ϯ 11-13 vertical coma (Z 3) with a mean value of 0.11 0.23 optimum optical performance once inside the human eye. µm. On average, the root-mean-square of higher order This discrepancy can be explained by the fact that, in the aberrations in pseudophakic eyes was 2.1 times that in a normal population of young myopic eyes. laboratory, the optical quality of the IOL is tested as a single unit, whereas the optical quality of the entire eye is mainly 14,15 CONCLUSIONS: Eyes that undergo cataract surgery governed by both the cornea and the IOL. Artal et al have with monofocal IOL implantation suffer from signifi cant shown that aberrations in the young cornea can be partially higher order aberrations. The optical design of the IOL is compensated by lenticular aberrations, resulting in an eye that most likely responsible for the increase in spherical ab- has better overall optical quality than either two components erration, the magnitude of which is a function of the di- optric power of the IOL. [J Refract Surg. 2006;22:237- alone. For this reason, inserting an optically “perfect” IOL into 242.] From Medical & Vision Research Foundation, Tamil Nadu, India (Padmanabhan, Rao, J, Choudhury); and the Center for Visual Science, University of Rochester, Rochester, NY (Yoon, Porter). The authors have no financial or proprietary interest in the materials pre- sented herein. Correspondence: Prema Padmanabhan, MS, Cornea Service, Sankara Nethralaya, 18 College Rd, Chennai 600 006, Tamil Nadu, India. Tel: 91 44 28271616; Fax: 91 44 28254180; E-mail: [email protected] Received: March 28, 2005 Accepted: April 25, 2005 Journal of Refractive Surgery Volume 22 March 2006 237 Wavefront Aberrations and Monofocal IOLs/Padmanabhan et al the eye will not yield a perfect overall system, devoid of stitutional review board and an informed consent was aberrations. Rather, the ideal IOL should contain aber- obtained from all patients. rations that are equal in magnitude and opposite in sign The ALLEGRETTO WAVE Analyzer (WaveLight La- to those inherent in an individual’s cornea. ser Technologies AG, Erlangen, Germany) was used to Other possible causes for a suboptimal optical per- measure each patient’s wave aberration. Measurements formance of an IOL implanted into an eye could be due were taken 2 weeks after surgery, when the eyes were to decentration of the IOL and possible changes in cor- believed to have attained refractive stability. A laser neal shape induced by the cataract wound. diode (wavelength of 532 nm) was used to produce a Clinical studies on the visual acuity and contrast collimated bundle of light, which was then split into a sensitivity of patients with monofocal or multifocal group of parallel rays by means of a mask with a regu- IOLs have been performed.16,17 These, however, are lar matrix of small apertures. The retinal image of the measures of both the optical and neural processes of spot pattern was photographed by a charged couple vision and do not directly describe the optical perfor- device camera. mance of the IOL. Artal et al18 used the double-pass The coordinates of the geometric centers of all im- measurements of the modulation transfer function aged retinal spots were determined by image process- (MTF) in eyes implanted with IOLs. Although the MTF ing software and computed by numerical fi tting to a is a good metric of retinal image quality, wavefront ab- Zernike expansion. The Zernike coeffi cients provided erration may be a more complete description of opti- by the aberrometer were converted to the notation rec- cal quality as it contains phase information as well.12 ommended by the Optical Society of America (OSA) The optical aberrations of eyes implanted with an IOL standard committee,20 using the normalization factors were only recently measured in vivo by Miller et al19 provided by the manufacturers. The 62 eyes analyzed in 11 patients using the Shack-Hartmann sensor and in this study included 31 right eyes and 31 left eyes. by Barbero et al12 in 9 eyes using the laser ray tracing The signs of all modes with odd symmetry about the technique. It is hoped that the present study, with its y-axis were negated in the left eyes to allow all eyes to relatively larger data set of 62 eyes, will add statisti- be analyzed together. Measurements were made with cal value to the observations made. Although Miller et a pupil diameter of at least 6 mm. Only well-centered al19 and Barbero et al12 observed an increase in posi- images were chosen for analysis. Zernike coeffi cients tive spherical aberration in eyes with IOLs, Barbero through the 6th order were measured and the root- et al12 showed that spherical aberration increased as mean-square (RMS) wavefront error of each order was a function of the IOL power. The present study also calculated. Higher order aberrations included the 3rd demonstrates a similar relationship and extends this through 6th order aberrations. relationship by providing a mathematical relationship These coeffi cients were compared with those of a between the postoperative spherical aberration and the normal dataset of 82 eyes of healthy young myopes power of the IOL. aged 19 to 48 years (mean 26.6Ϯ4.8 years) with refrac- The aims of the study were 1) to characterize and tive errors ranging from Ϫ0.75 to Ϫ8.50 D who attend- measure the ocular aberrations in eyes implanted with ed our refractive surgery clinic. IOLs, and 2) to study any correlation between postop- erative aberrations and surgical factors. RESULTS Figure 1 shows the mean values of all Zernike coeffi - PATIENTS AND METHODS cients from 3rd to 6th order, across a 6-mm pupil with This study analyzed 62 eyes from patients diag- error bars for the postoperative pseudophakic eyes. nosed with cataract aged between 40 and 74 years who The 1st and 2nd order aberrations have been deleted. underwent phacoemulsifi cation with implantation of a The most predominant aberrations that were statisti- foldable hydrophobic acrylic IOL (Acrysof MA60BM; cally signifi cantly greater than zero were spherical ab- 0 Ϯ р Alcon Laboratories Inc, Ft Worth, Tex) through a self- erration (Z4) measuring 0.37 0.16 µm (P .001), trefoil -3 Ϫ Ϯ sealing 4.1-mm frown incision between the 10 and 11 (Z 3) measuring 0.11 0.23 µm (P=.001), and vertical -1 Ϫ Ϯ Ͻ o’clock meridians. The power of the IOLs ranged from coma (Z 3) measuring 0.13 0.22 µm (P .001). 10.5 to 26.0 diopters. Eyes with any known ocular pa- Figure 2 shows the corresponding RMS values of thology (other than cataract) or previous ocular surgery each order and the overall higher order RMS error in were excluded from the study. Eyes that suffered any this group of pseudophakic eyes. The RMS of 3rd or- complication during surgery, including the loss of an der measured 0.44Ϯ0.25 µm and 4th order measured intact capsulorrhexis or a tear in the posterior capsule, 0.45Ϯ0.23 µm. The RMS of total higher order aberra- were also excluded. The study was approved by the in- tions was 0.67Ϯ0.34 µm. 238 journalofrefractivesurgery.com Wavefront Aberrations and Monofocal IOLs/Padmanabhan et al Figure 1.
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