Clinical outcomes and postoperative intraocular optical quality with a microincision aberration-free aspheric intraocular lens

ARTICLE

Clinical outcomes and postoperative intraocular optical quality with a microincision aberration-free aspheric intraocular lens Jorge L. Alio´, MD, PhD, David P. Pin˜ero, MSc, Dolores Ortiz, PhD, Rau´l Montalba´n, OD

PURPOSE: To evaluate the visual outcomes and optical quality with an aspheric intraocular lens (IOL) with no aberration in microincision cataract surgery. SETTING: Vissum-Instituto de Oftalmolo´gico de Alicante, Alicante, Spain. METHODS: This prospective cohort study included eyes that had cataract surgery with implantation of an Akreos Adapt Advanced Optics MI60 IOL. Surgery was performed using the Millennium phacoemulsification platform. The IOL was implanted through a sub-1.8 mm incision using the 1.8 Viscoglide cartridge. Visual and refractive outcomes were analyzed during a 12-month follow-up. In addition, postoperative ocular optical quality was evaluated using the Optical Quality Analysis System. Postoperative intraocular optical aberrations were calculated by subtracting corneal aberrations from total aberrations. RESULTS: The cohort comprised 25 eyes of 25 patients ranging in age from 52 to 83 years. The mean spherical equivalent was 0.47 diopters G 0.62 (SD) 3 months postoperatively (P Z .72). The mean corrected distance visual acuity improved from 0.54 G 0.23 logMAR preoperatively to 0.08 G 0.16 logMAR 3 months postoperatively (P<.01). Optical quality analysis showed a mean spatial frequency at 50% of the modulation transfer function (MTF) of 2.85 G 0.55 cycles per degree (cpd) and a mean cutoff MTF frequency of 21.50 G 7.02 cpd. Postoperatively, the mean intraocular spherical aberration was 0.16 G 0.11 mm and the mean primary coma root mean square, 0.23 G 0.15 mm. CONCLUSION: Implantation of the aberration-free aspheric IOL was safe and effective and provided excellent visual and refractive outcomes with good optical performance. J Cataract Refract Surg 2009; 35:1548–1554 Q 2009 ASCRS and ESCRS

Recent advancements in the field of intraocular lenses (IOLs) for cataract surgery include models with an aspheric design, which were developed to compensate for ocular spherical aberration.1 An example is the Tecnis Z9000 (Abbott Medical Optics, formerly Advanced Medical Optics), a biconvex IOL with a modified prolate anterior surface.2 The aspheric surface introduces negative spherical aberration to the ocular optical system to compensate for the positive spherical aberration of the cornea.2,3 Another aspheric IOL based on the same concept is the AcrySof IQ (Alcon Laboratories).4 This IOL and the Tecnis Z9000 are available for classic coaxial phacoemulsification procedures only. One concern about these aspheric IOLs is their limited potential benefit due to the surgical induction of astigmatism, higher-order aberrations (HOAs), or both.5 For this reason, aspheric IOLs were developed for microincision cataract surgery (MICS). Small1548

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incision phacoemulsification with foldable IOL implantation minimizes surgically induced astigmatism and corneal aberrations, resulting in better corneal optical quality postoperatively.5,6 Therefore, a more realistic aberrometric improvement could be expected with aspheric IOLs designed for MICS procedures, including the Acri.Smart 36A (Acri.Tec).7 Several studies3,4,7–10 report that aspheric IOLs provide better contrast sensitivity than standard spherical IOLs. In contrast, others11 found no differences in visual acuity and contrast sensitivity between aspheric IOLs and spherical IOLs despite the reduction in spherical aberration with aspheric models. In addition, aspheric IOLs are sensitive to positional changes.1,12 Significant degradation in optical quality can be induced by a malpositioned aspheric IOL, even when the tilt or decentration is slight.1,12 0886-3350/09/$dsee front matter doi:10.1016/j.jcrs.2009.03.055

ABERRATION-FREE ASPHERIC MICROINCISION IOL: OUTCOMES AND OPTICAL QUALITY

Recently, an aspheric IOL based on a different concept, the Akreos Adapt Advanced Optics MI60 (Bausch & Lomb), was introduced.13 This IOL has a neutral spherical aberration and thus does not modify the ocular spherical aberration. Therefore, it does not compensate for positive corneal spherical aberration. The flexibility of the IOL material allows it to be implanted through corneal incisions smaller than 1.8 mm. The current study evaluated the visual outcomes and the ocular optical quality after implantation of this aberration-free aspheric IOL using the MICS technique. PATIENTS AND METHODS This prospective cohort study included patients who had MICS and implantation of an aberration-free MICS IOL. Before surgery, all patients received a detailed explanation about the surgery and its risks and benefits, after which they signed an informed consent form in accordance with the Helsinki Declaration. Ethical committee approval was obtained for the study. Inclusion criteria were age between 50 years and 85 years, no history of eye surgery or glaucoma, a transparent central cornea, pupil dilation of at least 7.0 mm at the preoperative examination, absence of biomicroscopic signs of pseudoexfoliation, a normal fundus examination, and an endothelial cell count at the central cornea of at least 1600 cells/mm2. Patients with cataract other than nuclear or corticonuclear or with active ocular pathology were excluded from the study.

Patient Examinations Preoperatively, patients had a full ophthalmic examination including uncorrected (UDVA) and corrected (CDVA) distance visual acuities, manifest and cycloplegic refractions, slitlamp biomicroscopy, Goldmann tonometry, corneal topography, ultrasonic pachymetry (DGH-500 pachymeter,

Submitted: December 10, 2008. Final revision submitted: March 18, 2009. Accepted: March 23, 2009. From the Vissum Corporation–Instituto de Oftalmolo´gico de Alicante (Alio´, Pin˜ero, Ortiz, Montalba´n), Miguel Hernandez University (Alio´), and Departamento de O´ptica (Pin˜ero), Farmacologı´a y Anatomı´a, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain. No author has a financial or proprietary interest in any material or method mentioned. Supported in part by a grant of the Spanish Ministry of Health, Instituto Carlos III, Red Tema´tica de Investigacio´n Cooperativa en Salud Patologı´a Ocular del Envejecimiento, Calidad Visual y Calidad de Vida, Subproyecto de Calidad Visual (RD07/0062). Corresponding author: Jorge L. Alio´, MD, PhD, Research, Development, and Innovation Department, Vissum Corporation–Instituto de Oftalmolo´gico de Alicante, Avenida de Denia s/n, Edificio Vissum, 03016 Alicante, Spain. E-mail: [email protected].

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DGH Technology, Inc.), endothelial cell count (Konan SP5500, Konan Camera Research Institute), and fundus evaluation. All visual acuity measurements were completed using the Optec 3500 Vision Tester (Stereo Optical Co.), with visual acuity tested using a logMAR scale under controlled illumination conditions. In addition, ocular aberrometric analysis and ocular modulation transfer function (MTF) measurement were performed. Postoperative examinations were at 1 day and 1, 3, and 12 months and were performed by the same experienced examiner (R.M.). On the first postoperative day, a detailed slitlamp examination was performed to evaluate anterior segment integrity. Subsequent examinations included UDVA and CDVA measurement, slitlamp biomicroscopy, corneal topography and aberrometry, ocular aberrometry, and MTF evaluation. In addition to the clinical measures, intraocular optical aberrations were calculated.

Surgical Technique The same experienced surgeon (J.L.A.) performed all operations. Topical anesthesia (preservative-free lidocaine 2.0%) with mild sedation (1.0 to 3.0 mg midazolam) was used in all cases. Adequate dilation was obtained with intracameral mydriasis using 1.0 mL of a vial containing cyclopentolate 1.0% (1.0 mL), phenylephrine 10.0% (1.5 mL), lignocaine 2.0% (5.0 mL), and a balanced salt solution (10.0 mL). The incision was placed on the steepest corneal meridian, which was previously marked at the slitlamp to avoid cyclorotation. The Millennium phacoemulsification platform (Bausch & Lomb) was used for MICS, which was performed following a previously described protocol.5 The IOL was implanted through a sub-1.8 mm incision using a 1.8 Viscoglide cartridge (Medicel AG). Postoperative topical therapy included topical ofloxacin 0.3% and dexamethasone 0.1%.

Intraocular Lens This Akreos Adapt Advanced Optics MI60 is a singlepiece IOL consisting of a central optic and 4 flexible haptics (Figure 1). The biconvex aspheric IOL is of a hydrophilic acrylic material (26% water content) with an ultraviolet absorber. It has a 6.0 mm optic and a posterior angulation of 10 degrees. The optic edges are square to prevent posterior capsule opacification (PCO). The overall IOL length varies according to the optical power. The IOL is available in powers from C10.00 to C30.00 diopters (D).

Modulation Transfer Function The MTF was measured with the Optical Quality Analysis System (Visiometrics). This instrument is based on a doublepass technique and was developed for objective optical evaluation of the visual quality. In the double-pass technique, images of a point source are recorded after reflection on the retina and a double pass through the ocular media.14 The data were processed by software incorporated into the device, and the MTF was calculated. All measurements were performed with the pupil dilated (phenylephrine 10%). The spatial frequency at 50% of the MTF (0.5 MTF), which corresponds to a contrast modulation of 0.5, and the cutoff MTF frequency, which corresponds to a contrast modulation of 0, were calculated for a 5.0 mm pupil.

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Kolmogorov-Smirnov test. The Student t test for paired data was used for comparisons between preoperative data and postoperative data (visual acuity, intraocular aberrations, MTF parameters, Strehl ratio). A P value less than 0.05 was considered statistically significant.

RESULTS The cohort comprised 25 eyes of 25 patients with a mean age of 70 years (range 52 to 83 years). The mean power of the implanted IOLs was C22.02 G 2.67 D. The mean corneal incision measurement was 1.68 G 0.24 mm before IOL implantation and 1.82 G 0.16 mm after IOL implantation; the mean incision enlargement was 0.14 G 0.22 mm (range 0.10 to 1.20 mm). Refractive and Visual Outcomes Figure 1. The aberration-free aspheric IOL used in the study.

Intraocular Optical Quality Analysis Intraocular optical quality was evaluated by calculating the intraocular optical aberrations from the ocular and the anterior corneal aberration following a previously described procedure.15 Corneal aberrations were derived from the data of the anterior corneal surface obtained with a CSO corneal topography system (Costruzione Strumenti Oftalmici). The total ocular aberrations were measured with a Complete Ophthalmic Analysis System (Wavefront Sciences, Inc.), a high-resolution Hartmann-Shack aberrometer. Pupils were dilated (phenylephrine 10%) for the aberrometric study. Intraocular optical aberrations were calculated by subtracting the postoperative corneal aberrations from the total ocular aberrations 3 months after surgery using the Visual Optics Lab-CT software (version 6.89, Sarver and Associates) and a previously described procedure.15 The aberration coefficients and root-mean-square (RMS) values were calculated for a 5.0 mm pupil diameter. The following parameters were analyzed and recorded: total root mean square (RMS); higher-order RMS, which was computed for Zernike terms corresponding to 3rd order and higher; lower-order RMS, which was computed for terms of the 1st order and 2nd order; tilt RMS, which was computed for Zernike terms Z(1,G1); astigmatism RMS, which was computed for Zernike terms Z(2,G2); and primary coma RMS, which was computed for Zernike terms Z(3,G1). The corresponding Zernike coefficient for primary spherical aberration, Z(4,0), was also reported with its sign. In addition, the point-spread function (PSF) was obtained from the intraocular aberrations using Fourier analysis. The Strehl ratio was used as a single value representing the PSF. This parameter was obtained from the PSF by determining the ratio of peak focal light intensity in the analyzed PSF to the intensity in the ideal PSF (only diffraction-limited eye).

Statistical Analysis The SPSS statistical software package for Windows (version 15.0, SPSS, Inc.) was used for statistical analysis. Normality of all data samples was confirmed by the

Figure 2 shows the UDVA and CDVA over time. The mean UDVA was 0.31 G 0.22 logMAR 3 months postoperatively and 0.32 G 0.23 logMAR at 12 months; there were no statistically significant changes in UDVA during the follow-up (P Z .78). The mean CDVA was 0.54 G 0.23 logMAR preoperatively and 0.08 G 0.16 logMAR 3 months after surgery, which was a statistically significant increase (P!.01). No statistically significant changes in CDVA occurred during the remainder of the follow-up (P Z .35). Figure 3 shows the spherical equivalent (SE) over time. The mean SE was 0.69 G 2.97 D preoperatively and 0.47 G 0.62 D 3 months preoperatively; the difference was not statistically significant (P Z .72). No statistically significant changes were observed in this parameter during the remainder of the follow-up (P Z .22). Figure 4 shows the predictability. Of the eyes, 54.2% had an SE within G0.50 D and 79.2%, within G1.00 D.

Figure 2. Mean UDVA and CDVA over time. The error bars represent the standard deviation (CDVA Z corrected distance visual acuity; UDVA Z uncorrected distance visual acuity; VA Z visual acuity).

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Figure 3. Mean SE over time. The error bars represent the standard deviation (SE Z spherical equivalent).

Figure 4. Predictability (preoperative SE versus 3-month postoperative SE (SE Z spherical equivalent).

Modulation Transfer Function

designs were developed to try to compensate for corneal aberrations and avoid the induction of aberrations. In our study, we used an IOL with a new design and with a neutral spherical aberration. We evaluated the visual and refractive outcomes in eyes with this IOL and characterized the optical performance of the IOL in vivo using a mathematical method that has been described in detail.15 In our study, the visual outcomes with the aberration-free aspheric IOL were excellent, with significantly better CDVA after surgery than before surgery. These results agree with those reported by Johansson et al.13 using an Akreos IOL with the same design as the Akreos MI60 model but that was not designed for MICS. Our results also agree with findings in studies of other types of aspheric IOLs designed to compensate for corneal aberrations.3,4,7–11,13 Specifically, Johansson et al.13 compared the outcomes in eyes with the aspheric IOL Tecnis Z9000 (compensates for corneal spherical aberration) and eyes with the aberration-free aspheric Akreos IOL but in the model not for MICS the 2 IOL models yielded similar visual acuity and contrast sensitivity outcomes. We used a double-pass system to evaluate the postoperative optical quality using ocular MTF values. This system evaluates global optical quality in addition to the optical performance of the implanted IOL. Global optical quality is affected by the optical properties of the IOL as well as by the corneal aberrometric changes after cataract surgery. We used the doublepass system to evaluate 2 parameters: 0.5 MTF and cutoff MTF frequency. The cutoff MTF is the maximum spatial frequency the human eye can detect; it has a theoretical relationship with visual acuity in eyes with good macular and neuroprocessing function. Therefore, the higher the cutoff frequency, the higher the ability of the ocular system to detect fine details and thus the better the ocular optical quality. The 0.5 MTF represents the spatial frequency needed in an object for its contrast to be degraded by 50% when its image is formed on the retina by the ocular optics. As

Figure 5 shows the MTF in 1 eye measured using the double-pass device. Three months postoperatively, the mean 0.5 MTF was 2.85 G 0.55 cycles per degree (cpd) and the mean cutoff MTF frequency, 21.50 G 7.02 cpd. Twelve months after surgery, the means were 2.61 G 0.59 cpd and 17.46 G 6.68 cpd, respectively. The difference in the values between 3 months and 12 months was statistically significant (both P Z .02). Intraocular Optical Quality Figure 6 shows the postoperative intraocular aberrations. The mean total RMS was 1.65 G 0.59 mm and the mean higher-order RMS, 0.51 G 0.14 mm. The mean spherical aberration was 0.16 G 0.11 mm. Low levels of primary coma (mean 0.23 G 0.15 mm) were also found. The mean Strehl ratio for intraocular optics was 0.26 G 0.03. Figure 7 shows the intraocular aberration calculation in 1 case. Complications There were no intraoperative complications. Postoperatively, 9 eyes (36.0%) developed PCO that was successfully treated with a neodymium:YAG capsulotomy. One IOL haptic that was located outside the capsular bag was successfully repositioned in 1 eye at 1 month. DISCUSSION Cataract surgery can cause degradation in ocular optical quality. One source of the degradation is surgically induced changes in the anterior corneal profile, which can lead to an increase in astigmatism and HOAs. The introduction of MICS surgery, which is performed through a sub-2.0 mm incision, has minimized the effect of these factors.5,6 Another source of optical quality degradation is the optical performance of the implanted IOL. The aberrometric balance between the cornea and the crystalline lens is destabilized by lens extraction and IOL implantation. Thus, new IOL

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Figure 5. Example of MTF measurements obtained with the doublepass system (CSF Z contrast sensitivity function; MTF Z modulation transfer function; VA Z visual acuity).

with the cutoff MTF frequency, the higher the 0.5 MTF value, the better the optical quality. The mean ocular 0.5 MTF and mean ocular cutoff MTF frequency values in our study are similar to those in young, healthy eyes and higher than those in older eyes.16 In addition, the mean ocular cutoff MTF frequency obtained with the IOL we used is better than that reported for spherical monofocal IOLs for MICS (21.50 G 7.02 cpd versus 8.81 G 4.38 cpd for the UltraChoice 1.0 ThinOptX and 11.42 G for the 2.57 Acri.Smart 48S).17 In addition to the visual, refractive, and optical quality outcomes, we evaluated the intraocular optical quality, which is in direct relation to the in vivo optical performance of the IOL. To do this, we subtracted the anterior corneal aberrations from the ocular aberrations in a procedure used in previous studies to characterize other IOLs (monofocal and multifocal).15,18

Figure 6. Mean intraocular aberration values G SD obtained with the corneal topography and wavefront analysis software (RMS Z root mean square; RMS HO Z higher-order root mean square; RMS LO Z lower-order root mean square; RMS Tot Z total root mean square).

According to the manufacturer of the Akreos Adapt Advanced Optics MI60, the IOL has neutral aberrometric behavior; that is, it does not induce spherical aberration and thus does not compensate for corneal spherical aberration. In this study, the aberrometric behavior of the IOL in vivo was inferred from the analysis of the intraocular optical quality of the eye with the IOL. To our knowledge, this is the first published study characterizing the aberrometric behavior of this aberration-free IOL. Our in vivo assessment of intraocular optics performance with the IOL provides useful objective information about its stability and the potential for optical disturbances after implantation. The findings provide information (about intraocular changes without consideration of corneal changes) that complements that obtained with the double-pass system. The posterior corneal surface, which is included in the intraocular optical quality analysis, has a limited contribution to the global aberrations because of the small change in refractive index at this surface.19,20 Indeed, it has been shown that the posterior surface compensates for approximately 3.5% of the coma of the anterior surface19 and it is affected by minimal positive spherical aberration at older ages.20 Johansson et al.13 analyzed global ocular aberrations after implantation of the Akreos Adapt Advanced Optics IOL. Their aberrometric information also included the effect of anterior corneal aberrations; thus, their outcomes cannot be compared with ours because they did not consider intraocular aberrations. In our study, the intraocular spherical aberration with the IOL was minimal, as expected. The mean

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Figure 7. Example of the maps and graphs obtained with the corneal topography and wavefront analysis software. Top left: In vivo intraocular aberrations map for 6.0 mm pupil. Top right: The 3-dimensional PSF. Bottom left: Modulation transfer function graph obtained by Fourier analysis. Bottom right: Optotype simulation (cpd Z cycles per degree; MTF Z modulation transfer function; PSF Z point-spread function; RMS HO Z higherorder root mean square; RMS LO Z lower-order root mean square; RMS TOT Z total root mean square).

spherical aberration was approximately 0.16 mm; this low value can be explained by the small amount of positive spherical aberration induced by the posterior corneal surface.19,20 In addition, we found low levels of induced intraocular coma. Part of this small amount of coma was likely induced by the posterior corneal surface,19 indicating that the IOL does not induce coma aberration. The levels of intraocular primary spherical aberration and coma with this IOL are similar to those reported previously with other spherical and multifocal IOLs.15 Finally, we found a mean intraocular tilt of 1.20 G 0.58 mm. This moderate level of tilt could be explained in part by an oblique IOL position inside the capsular bag. Intraocular lenses in the capsular bag tend to tilt and decenter nasally.21 Spherical aberration-free IOLs are less affected by tilt and decentration than other types of IOLs because they do not induce aberrations and the IOL’s optical performance is not affected by positional changes.22 Our study had a significant PCO rate. The incidence was 35% after 1 year of follow-up, which is moderate to high compared with percentages reported for other types of IOLs23 and for previous models of the Akreos IOL.24 There were no severe complications in our study. In conclusion, our results show that implantation of the Akreos Adapt Advanced Optics MI60 IOL provides excellent visual and refractive outcomes. The aberration-free IOL also has excellent optical performance and provides good visual quality. Based on the significant incidence of PCO, future designs of

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First author: Jorge L. Alio´, MD, PhD Vissum Corporation-Instituto de Oftalmolo´gico de Alicante and Miguel Hernandez University, University of Alicante, Alicante, Spain