Optical performance of monofocal and multifocal intraocular lenses in the human eye

ARTICLE

Optical performance of monofocal and multifocal intraocular lenses in the human eye Dolores Ortiz, PhD, Jorge L. Alio´, MD, PhD, Gonzalo Bernabe´u, MD, Vanessa Pongo, MD

PURPOSE: To study the optical performance of intraocular lenses (IOLs) in the human eye to ascertain how multifocality affects the optical performance of refractive and diffractive technologies and the relationship to pupil size. SETTING: Vissum-Instituto de Oftalmolo´gico de Alicante, Alicante, Spain. METHODS: Ten eyes each received the monofocal AcrySof MA60 IOL (Alcon) or 1 of the following multifocal pupil-dependent IOLs: diffractive AcrySof ReSTOR (Alcon) or refractive ReZoom (Advanced Medical Optics). The intraocular optical quality in vivo with 3.0 mm and 5.0 mm pupils was characterized by comparing the means of the difference between the total and corneal optical aberrations 3 months postoperatively. The main outcomes measures were total, higher-order, spherical, and coma aberrations (root-mean-square values); modulation transfer function values; point-spread function; and the Strehl ratio. RESULTS: The ReZoom group had higher in vivo intraocular aberrations than the AcrySof ReSTOR and AcrySof MA60 groups (P Z .022). The difference in spherical aberration between the AcrySof ReSTOR and ReZoom groups was statistically significant with 5.0 mm pupils (P Z .003) and 3.0 mm pupils (P Z .001). The AcrySof ReSTOR group had statistically significant lower coma aberration values with a 5.0 mm pupil (P Z .012); there were no differences between IOLs with a 3.0 mm pupil (P Z .185). CONCLUSIONS: Multifocal refractive IOLs resulted in higher intraocular aberrations. The hybrid refractive–diffractive IOL was the least affected by pupil diameter in terms of intraocular aberrations and showed significantly less increase in optical aberrations when the pupil was enlarged. J Cataract Refract Surg 2008; 34:755–762 Q 2008 ASCRS and ESCRS

Intraocular lenses (IOLs) were a major step forward in the correction of aphakia after cataract surgery. Since their invention by Ridley1 in the 1950s, IOLs have improved significantly, principally due to their use for Accepted for publication December 12, 2007. From Vissum-Instituto de Oftalmolo´gico de Alicante (Ortiz, Alio´, Bernabe´u, Pongo) and Miguel Herna´ndez University (Alio´), Alicante, Spain. No author has a financial or proprietary interest in any material or method mentioned. Supported in part by a grant from the Spanish Ministry of Health, Instituto Carlos III, Red Tema´tica de Investigacio´n en Oftalmologı´a, Subproyecto de Cirugı´a Refractı´va y Calidad Visual (C03/13). Corresponding author: Jorge L. Alio´, MD, PhD, Research and Development Department, Vissum-Instituto de Oftalmolo´gico de Alicante, Avenida de Denia s/n, Edificio Vissum, 03016 Alicante, Spain. E-mail: [email protected]. Q 2008 ASCRS and ESCRS Published by Elsevier Inc.

refractive correction, including presbyopia. Thus, current IOLs must provide increased quality and optical performance after cataract removal. Today’s sophisticated designs, such as multifocal IOLs, were developed to improve postoperative near vision and reduce spectacle dependence.2–4 However, the multifocal optic can cause decreased contrast sensitivity and lead to halos and glare.5–7 The measurement of the imaging quality of IOLs provided by manufacturers is based on standardized methods that evaluate IOL optical quality ex vivo8–10 (in air or water) at an optical bench or by simulation using an artificial eye model.11 Although theoretically and technically precise, the information provided by these industrial models is limited from the clinical perspective as it does not take into account the individual characteristics of the eye (corneal power, anterior chamber, axial length, pupil location and size) or the off-center elements of the eye’s diopters (D). In particular, these forms of evaluation do not reproduce the 0886-3350/08/$dsee front matter doi:10.1016/j.jcrs.2007.12.038

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postsurgical condition of the eye as the IOL may tilt or decenter once implanted due to IOL damage during implantation or complications during surgery, among other reasons. For multifocal IOLs, industrial models should consider the influence and effect of pupil size on the optical performance of the IOL because the concept of multifocal optics is based on pupil behavior under different lighting conditions. With the introduction of modern ocular measurements and technical improvements (corneal topography, wavefront evaluation, double-pass techniques), general knowledge of the optical performance12 of the eye has improved and theoretical calculations using sophisticated software13–16 have become relevant tools for obtaining objective estimates about individual eyes. Combining measurements of corneal and ocular aberrations, the optical quality of the IOL in vivo can be obtained by subtraction.9,15,17 Information about the in vivo performance of an IOL would help surgeons make better choices about the best IOL to implant in each patient and determine the reasons for symptoms after IOL implantation. The purpose of this study was to evaluate the optical quality and performance in vivo of 1 monofocal IOL and 2 multifocal pupil-dependent IOLs with different optical technology to ascertain whether there are differences in optical performance between diffractive and refractive multifocal IOL technologies depending on pupil size. In this way, the validity and applicability of an objective clinical model used to obtain information on intraocular aberrations of the IOLs in the human eye will be shown. To our knowledge, this is the first study that separately analyzes the optical performance of the IOL in the human eye with special attention to the effect of changes in pupil size. PATIENTS AND METHODS This prospective interventional comparative nonrandomized clinical investigation study included 30 eyes of 15 patients. Of the 30 eyes, 10 each had implantation of the monofocal AcrySof MA60 IOL (Alcon) or 1 of the following multifocal pupil-dependent IOLs: the apodized diffractive AcrySof ReSTOR (Alcon) or the refractive ReZoom (Advanced Medical Optics). The 2 typical designs of multifocality (diffractive and refractive) were evaluated and compared with the standard IOL (monofocal). Patients with an irregular corneal topography pattern, previous corneal surgery, retinal pathology, or a history of ocular disease were excluded from the study. Patient age was irrelevant in this study as the aim was not to evaluate the visual and refractive outcomes of the 3 IOLs but rather to assess the individual optical performance of the IOLs after lensectomy. All eyes had good pupil dilation (R7.0 mm). All patients signed an informed consent in accordance with the tenets of the Helsinki Declaration. Investigative review board and ethics committee approval was not required for the study.

Surgical Technique Microincision cataract surgery (MICS) was performed by the same surgeon (J.L.A.) through a 1.6 to 1.8 mm clear corneal incision placed on the axis of the positive corneal meridian using a previously described protocol.18,19 After MICS, the incision was enlarged to an adequate size (approximately 3.0 mm) for IOL implantation. AcrySof MA60 IOLs were implanted using a Monarch I injector (Alcon); ReZoom IOLs, using an Emerald injector (Advanced Medical Optics); and AcrySof ReSTOR IOLs, using a Monarch II injector (Alcon). The IOL power was calculated by the SRK/T formula; the target was emmetropia in all cases.

Patient Evaluation Preoperative assessment consisted of a complete ophthalmologic examination including topography (CSO corneal topography system, Costruzione Strumenti Oftalmici), biometry (IOLMaster, Zeiss), near and distance visual acuities, and refraction. Distance decimal visual acuity was tested using the decimal scale visual charts at 4 m and near visual acuity, with the Early Treatment Diabetic Retinopathy Study chart at 40 cm. These procedures were performed under normal lighting conditions (approximately 90 cd/m2) using 100% contrast optotypes. Postoperative follow-up examinations were performed at 1 day, 1 week, and 1 and 3 months. In this study, only the 3-month data were used. The main outcomes measures were total, higher-order, spherical, and coma intraocular aberrations (root-meansquare [RMS] value); 0.5 and cutoff modulation transfer function (MTF) values; and the Strehl ratio with 2 pupil sizes. The RMS and MTF values and the Strehl ratio were obtained with 3.0 mm and 5.0 mm pupil diameters in all cases.

Intraocular Lenses The AcrySof MA60 is a monofocal 3-piece acrylic IOL. It has a 6.0 mm optic and a biconvex shape. The AcrySof ReSTOR IOL2,20,21 is designed to provide quality near to distance vision by combining apodized diffractive and refractive technologies. Apodization is the gradual tapering of diffractive steps from the center to the outside edge of a lens to create a smooth transition of light between the distance, intermediate, and near focal points. On the AcrySof ReSTOR IOL, the center of the lens surface consists of an apodized diffractive optic (3.6 mm diameter) that focuses light for near through distance. The refractive region of the AcrySof ReSTOR IOL bends light as it passes through the lens to a focal point on the retina. This outer ring of the AcrySof ReSTOR IOL surrounds the apodized diffractive region and is dedicated to focusing light for distance vision. This IOL effectively restores near and distance vision regardless of pupil size. In bright light with constricted pupils, the lens sends light energy simultaneously to both near and distant focal points. In low light with dilated pupils, the apodized diffractive lens sends a greater amount of energy to distance vision to minimize visual disturbances. The ReZoom22 is a clear foldable IOL of a high-refractiveindex acrylic material. The second-generation refractive multifocal IOL distributes light over 5 optic zones so that each lens has a distance-dominant central zone for distance vision under bright-light conditions when the pupil is constricted. In the refractive profile, the odd zones (1, 3, and 5) are adjusted for far vision and the even zones (2 and 4), for near vision, giving an addition of 3.5 D. Therefore, the optical

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behavior of the IOL depends on pupil size. With a small pupil, light energy is sent to distance vision. When pupil size increases, the IOL sends light energy simultaneously to both near and distant focal points.

Objective Measurement of the Intraocular Optical Quality of Intraocular Lenses The intraocular optical quality of the IOLs was estimated by calculating the intraocular optical aberrations of the total eye and the anterior corneal aberration. Measurements were taken by an independent examiner under controlled environmental conditions. Corneal aberrations were derived from the data of the anterior surface of the cornea obtained from the CSO topographer. The software of the CSO system, EyeTop2005, converts the corneal elevation profile into corneal wavefront data using Zernike polynomials with an expansion up to the 7th order. The system analyzes 6144 corneal points from a corneal zone between 0.33 mm and 10.0 mm in respect to the corneal vertex. The ocular aberrations were measured with the Complete Ophthalmic Analysis System (Wavefront Sciences Inc.), a high-resolution Hartmann-Shack aberrometer. The aberrometer has a spatial resolution of 210 mm and analyzes 872 samples for a pupil up to 7.0 mm. Measurements were repeated at least 3 times to obtain a well-focused, aligned image of the eye. Measurements were taken for the maximum pupil diameter and then analyzed for 3.0 mm and 5.0 mm pupils. For the aberrometric study, pupils were dilated with 2 drops of cyclopentolate 10% given 15 minutes apart and 1 drop of phenylephrine 10%. Measurements were taken 45 minutes after the last cyclopentolate drop was instilled. The in vivo optical quality was assessed using Visual Optics Laboratory (VOL) software14 (version 6.89, Sarver and Associates, Inc.) by comparing the means of the difference

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between postoperative total and corneal optical aberrations 3 months after surgery. The difference between the aberrations was calculated by subtraction in which both maps referred to the pupil center; therefore, the measurement axis was the same since the conditions of illumination are the same for the places in which both devices (topographer and aberrometer) are placed. The software allows the user to introduce the offset between maps in cases in which the pupil diameters of the 2 measures are different to introduce a realignment algorithm in the calculations of the difference. Figure 1 shows an example of the maps obtained using VOL software of an eye with an AcrySof MA60 IOL. The aberration coefficients and RMS values were obtained and analyzed for 3.0 mm and 5.0 mm pupil diameters in all cases. The MTF and the point-spread function (PSF) were obtained from the intraocular aberrations by Fourier analysis. The spatial frequencies at the 0.5 MTF and cutoff MTF of the different curves of the IOLs were analyzed. Data of the 0.5 MTF represent the spatial frequency (cycles per degree [cpd]) at which the image contrast is degraded 50% compared with the object contrast. Data of cutoff MTF represent the highest spatial frequency (cpd) the optical system is able to detect. At this frequency, the image contrast is degraded 99% compared with the object contrast and corresponds to the maximum resolution of the optical system. The Strehl ratio23–25 was obtained from the PSF by the quotient between the maximum intensities of light energy of a real system and a diffraction-limited system. This parameter should be as close as possible to the value of 1 (perfect optical system) and is related with the ability of the eye to produce a point image on the retina when a point object is observed.

Statistical Analysis Statistical analysis was performed using SPSS for Windows (version 11.0.1, SPSS, Inc.). The Kruskal-Wallis test

Figure 1. Example of the maps and graphs obtained by the VOL software for a typical eye with an AcrySof MA60 IOL. Top left: In vivo intraocular aberrations map with a 5.0 mm pupil. Top right: A 3dimensional PSF map. Bottom left: The PSF and MTF graphs obtained by Fourier analysis. Bottom right: E-Snellen simulation (MTF Z modulation transfer function; RMS Z root mean square).

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Table 1. Preoperative clinical data. Mean G SD Group

SE (D)

MA60 (nZ 10) ReSTOR (n Z 10) ReZoom (nZ 10)

1.9 G 3.1 1.4 G 3.1 1.4 G 3.9

BCVA

IOL Power (D)

0.6 G 0.2 0.9 G 0.2 0.7 G 0.2

22.3 G 3.6 22.3 G 4.7 19.8 G 5.1

BCVA Z best corrected visual acuity; IOL Z intraocular lens; SE Z spherical equivalent

was used to compare the mean values in the 3 IOL groups. The results were subjected to Bonferroni post hoc statistical analysis to identify which groups were significantly different. A P value of 0.05 or less was considered statistically significant.

RESULTS There were no intraoperative complications in any case. Refractive Outcomes Table 1 shows the preoperative spherical equivalent (SE), best corrected visual acuity (BCVA), and IOL power in the 3 IOL groups. The BCVA in the AcrySof ReSTOR group was statistically significantly better than in the AcrySof ReSTOR and AcrySof MA60 groups (P Z .006). There were no significant differences between groups in SE or IOL power. The multifocal IOL groups had a positive (slightly hyperopic) defocus and statistically significant less defocus than the AcrySof MA60 group (P Z .001) (Table 2), and this defocus provided a slightly myopic SE. The near UCVA was statistically significantly better in the AcrySof ReSTOR group than in the ReZoom IOL group (P Z .028). Analysis of Intraocular Lens Aberrations Figure 2 shows typical examples of in vivo IOL aberration maps for the 3 IOLs with 3.0 mm and 5.0 mm pupils. Also shown are E-Snellen simulations

Table 2. Visual and refractive outcomes 6 month after surgery. Mean G SD

UCVA

BCVA

Near UCVA

Group

SE (D)

MA60 (nZ 10) ReSTOR (n Z 10) ReZoom (nZ 10)

0.7 G 0.4 0.6 G 0.2 0.9 G 0.1 d 0.2 G 0.3 0.8 G 0.1 1.0 G 0.1 0.9 G 0.1 0.2 G 0.4 0.8 G 0.2 0.9 G 0.1 0.7 G 0.1

BCVA Z best corrected visual acuity; SE Z spherical equivalent; UCVA Z uncorrected visual acuity

obtained using the global ocular aberrations in the sample eyes. Figure 3 shows the PSF and MTF graphs and standard optotype simulation of the 3 IOLs obtained using in vivo intraocular aberration with a 5.0 mm pupil. Table 3 shows the in vivo optical aberrations (total, lower order, and higher order) and the MTF results in the 3 IOL groups with 3.0 mm and 5.0 mm pupils. The optical aberration values with a 5.0 mm pupil were higher than those with a 3.0 mm pupil. With a 5.0 mm pupil, the AcrySof ReSTOR group had statistically significantly lower total, lower-order, and higherorder aberrations than the ReZoom IOL group (P Z .003). The optical aberrations with a 3.0 mm pupil decreased in all groups, with the ReZoom IOL having a higher RMS value than the AcrySof ReSTOR or AcrySof MA60 group; the ReZoom IOL group had statistically significantly higher higher-order aberrations (HOAs) with a 3.0 mm pupil than the other 2 IOL groups (P Z .022) Pupil diameter had a greater influence on the 0.5 MTF value than on the cutoff MTF value with all IOLs (Table 3). The 0.5 MTF value was highest in the AcrySof ReSTOR group with both pupil diameters. With a 3.0 mm pupil, the difference was statistically significant between the AcrySof ReSTOR group and the ReZoom group (P Z .033). The ReZoom IOL group had a higher cutoff MTF value with a 5.0 mm pupil; however, the difference in cutoff MTF values between the 3 groups was not statistically significantly different with either pupil size (P Z .066, 5.0 mm; P Z .888, 3.0 mm). In a separate analysis of HOA, the mean spherical aberration with a 3.0 mm pupil and a 5.0 mm pupil was, respectively, 0.015 mm G 0.01 (SD) and 0.16 G 0.17 mm in the AcrySof MA60 group, 0.03 G 0.02 mm and 0.06 G 0.04 mm in the AcrySof ReSTOR group, and 0.14 G 0.10 mm and 0.17 G 0.07 mm in the ReZoom group (Figure 4). With a 5.0 mm pupil, the AcrySof ReSTOR group had the lowest value and the difference between the ReSTOR group and the ReZoom group was statistically significant (P Z .003). With a 3.0 mm pupil, the AcrySof ReSTOR group and AcrySof MA60 group had comparable spherical aberration values and both groups had statistically significantly lower values than the ReZoom group (P Z .001). The mean coma aberration with a 3.0 mm pupil and a 5.0 mm pupil was 0.04 G 0.02 mm and 0.20 G 0.15 mm, respectively, in the AcrySof MA60 group; 0.03 G 0.02 mm and 0.09 G 0.04 mm, respectively, in the AcrySof ReSTOR group; and 0.09 G 0.08 mm and 0.22 G 0.14 mm, respectively, in the ReZoom group (Figure 5). With a 3.0 mm pupil, all IOL groups had low coma values and there were no statistically

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Figure 2. Comparative maps of the in vivo intraocular wavefront of the 3 IOLs with a 3.0 mm pupil (top row) and 5.0 mm pupil (center row). Bottom row: E-Snellen simulation considering the total ocular aberrations with a 5.0 mm pupil.

significant differences between groups (P Z .185). With a 5.0 mm pupil, the AcrySof ReSTOR group had the lowest value and the difference between the ReSTOR group and the ReZoom group was statistically significant (P Z .012).

Figure 6 shows the mean Strehl ratio values with a 3.0 mm pupil and a 5.0 mm pupil in all IOL groups. There were no statistically significant differences between groups with either pupil size (P Z .899, 5.0 mm; P Z .324, 3.0 mm).

Figure 3. Comparative maps of the in vivo intraocular PSF (top row) and MTF (middle row) of the 3 IOLs with a 5.0 mm pupil (MTF Z modulation transfer function; RMS Z root mean square). Bottom row: Snellen optotype simulation considering the total ocular aberrations with a 5.0 mm pupil.

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Table 3. In vivo optical aberrations and optical quality. Mean RMS (mm) G SD Group/Pupil Size (mm) MA60 3.0 5.0 ReSTOR 3.0 5.0 ReZoom 3.0 5.0

Mean MTF (cpd) G SD

Total

Lower Order

Higher Order

0.5

Cutoff MTF

0.28 G 0.06 0.97 G 0.20

0.27 G 0.06 0.85 G 0.17

0.08 G 0.03 0.37 G 0.32

4.4 G 1.0 1.9 G 0.3

54.0 G 11.2 49.8 G 21.7

0.25 G 0.12 0.84 G 0.41

0.24 G 0.12 0.80 G 0.41

0.08 G 0.05 0.22 G 0.08

6.1 G 4.5 3.1 G 2.7

53.1 G 12.2 53.6 G 32.5

0.36 G 0.14 0.99 G 0.46

0.27 G 0.12 0.86 G 0.48

0.23 G 0.10 0.44 G 0.13

2.9 G 1.2 1.8 G 0.6

53.3 G 8.4 69.2 G 15.5

cpd Z cycles per degree; MTF Z modulation transfer function; RMS Z root mean square

DISCUSSION In this study, the intraocular optical quality and performance in vivo of a monofocal IOL (AcrySof MA60) and 2 pupil-dependent multifocal IOLs (diffractive AcrySof ReSTOR and refractive ReZoom) were evaluated by an objective clinical model based on VOL-CT software. The in vivo assessment of IOL performance may provide useful objective information about each IOL’s stability and potential optical disturbances after implantation as well as the relationship with pupil size. Other authors9,17 used a similar method to study the in vivo optical quality of monofocal IOLs; however, to our knowledge, ours is the first study to analyze the differences in in vivo optical performance between IOLs with different optical profiles that could be influenced by pupil size. In our study, the intraocular optical quality of the IOLs was characterized by the aberration coefficients and RMS values, obtained and analyzed with 3.0 mm and 5.0 mm pupil diameters, and by the MTF and the PSF, calculated from the intraocular aberrations by Fourier analysis. All values affect visual quality.

Coma aberration provides information on whether the IOL is properly centered. Spherical aberration is correlated with symptoms such as halos and glare. The spatial frequency at 0.5 MTF is connected to contrast sensitivity at low frequencies, and the cutoff MTF value and Strehl ratio provide information on visual acuity. The model showed that pupil diameter had an important influence on the optical performance of the 3 IOLs evaluated, with performance decreasing with increasing pupil size. This was especially true in the monofocal AcrySof MA60 IOL group, which had the highest increase in spherical and coma aberrations when the pupil diameter increased from 3.0 to 5.0 mm. The AcrySof ReSTOR IOL was the least affected by pupil diameter due to its apodized design,26 which is similar to that of an optical filter. The apodized design causes the light that passes near the edge of the pupil to be less effective on the retinal image than light that passes through the center of the pupil. The multizone design of the ReZoom IOL produces more sensitivity to decentration when the pupil increases, and the

Figure 4. In vivo spherical aberration of all IOL groups with 3.0 mm and 5.0 mm pupils (RMS Z root mean square).

Figure 5. In vivo coma aberration in all IOL groups with 3.0 mm and 5.0 mm pupils (RMS Z root mean square).

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Figure 6. In vivo Strehl ratio in all IOL groups with 3.0 mm and 5.0 mm pupils.

coma aberration values were highest in the ReZoom group. In vivo optical quality in terms of the 0.5 MTF value was better with both pupil diameters in the AcrySof ReSTOR group. There was no significant difference between groups in the cutoff MTF value and Strehl ratio, which was evidenced by the good postoperative visual acuity in all 3 groups. Regarding the RMS values, the AcrySof ReSTOR group had lower mean total aberration and HOAs with a 5.0 mm pupil than the monofocal and multifocal refractive IOL groups. This result is consistent with findings in a previous study of more than 50 eyes by Rocha et al.26 The authors found a mean total aberration and HOA for the AcrySof ReSTOR IOL of 0.72 G 0.25 mm and 0.35 G 0.15 mm, respectively, with the same pupil size. With a 3.0 mm pupil, the AcrySof ReSTOR IOL and AcrySof MA60 IOL had comparable values that were significantly lower than ReZoom IOL values. Spherical aberration values with a 5.0 mm pupil were lower with the AcrySof ReSTOR IOL than with the AcrySof MA60 IOL; the values with a 3.0 mm pupil were comparable between the 2 IOLs. The coma aberration values with a 3.0 mm pupil were comparable between the 3 IOLs, although the AcrySof ReSTOR IOL had the lowest values with a 5.0 mm pupil. Our in vivo optical aberration results for the monofocal AcrySof MA60 are comparable to the in vivo aberrations reported for other standard spherical monofocal IOLs. For HOAs, Marcos et al.17 report an RMS value of 0.4 mm with a 4.5 mm pupil and Barbero et al.,9 of 0.5 mm with a 6.0 mm pupil. For coma aberration, Marcos et al. report an RMS value of 0.35 mm with a 4.5 mm pupil and Barbero et al., of 0.4 mm with a 6.0 mm pupil. For spherical aberration, Marcos et al. report an RMS value of 0.2 mm with a 4.5 mm pupil and Barbero et al., of 0.25 mm with a 6.0 mm pupil. In our study, the actual in vivo optical quality provided by the AcrySof MA60 spherical monofocal IOL

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was lower in terms of the Strehl ratio and MTF values than the optical quality ex vivo provided by industry model based on measurements for another standard spherical monofocal IOL on the optical bench, reported by Rawer et al.8 For a 3.0 mm pupil, Rawer et al. report a Strehl ratio of 0.85 (0.40 in our study) and a 0.5 MTF value of 30 cpd (4.4 cpd in our study). This result shows a discrepancy between theoretical design, final IOL manufacturing, and experimental handling.9 Previous studies25–29 have analyzed the differences between IOLs in terms of global ocular aberrations; however, this information is affected by the corneal aberrations of the individual eye. This should be taken into account when analyzing the results of the comparisons between IOLs. The most important limitation of our study was the number of eyes analyzed for every IOL, although the number is similar to or higher than in other studies.9,17,25 A higher number of cases would provide more accurate IOL aberration data and better show statistically significant differences between IOLs. In conclusion, the pupil-dependent multifocal hybrid IOL with a 3.6 mm central diffractive area showed better in vivo optical performance in terms of spherical aberration than monofocal and multifocal refractive IOLs. The differences between IOLs were greater when the pupil increased from 3.0 to 5.0 mm, with the diffractive hybrid AcrySof ReSTOR IOL the least affected by pupil diameter in terms of intraocular aberrations. The increase in optical aberrations when the pupil was enlarged from 3.0 to 5.0 mm was compensated for by the hybrid design of the refractive–diffractive IOL. Our objective clinical model to evaluate in vivo optical performance can be used for all IOL types and can provide information on differences in optical quality based on objective data. Such information will help surgeons choose the best IOL for each patient. Future studies of symptomatic cases (eg, with halos or glare) will make it possible to establish the connection between the in vivo performance of the IOL and the symptoms of the individual patient. REFERENCES 1. Apple DJ, Sims J. Harold Ridley and the invention of the intraocular lens. Surv Ophthalmol 1996; 40:279–292 2. Alio´ JL, Tavolato M, De la Hoz F, et al. Near vision restoration with refractive lens exchange and pseudoaccommodating and multifocal refractive and diffractive intraocular lenses; comparative clinical study. J Cataract Refract Surg 2004; 30:2494–2503 3. Brydon KW, Tokarewicz AC, Nichols BD. AMO Array multifocal lens versus monofocal correction in cataract surgery. J Cataract Refract Surg 2000; 26:96–100 4. Sen HN, Sarikkola A-U, Uusitalo RJ, Laatikainen L. Quality of vision after AMO Array multifocal intraocular lens implantation. J Cataract Refract Surg 2004; 30:2483–2493

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J CATARACT REFRACT SURG - VOL 34, MAY 2008

First author: Dolores Ortiz, PhD Vissum-Instituto de Oftalmolo´gico de Alicante, Alicante, Spain