comparison of pseudophakic visual quality in spherical and aspherical intraocular lenses

274 CAN J OPHTHALMOL—VOL. 44, NO. 3, 2009

Comparison of pseudophakic visual quality in spherical and aspherical intraocular lensesHongguang Cui, MD; Rongrong Hu, MD; Yingying Zhang, MD; Dinghua Lou, MD

Objective: This study compares the visual performance of spherical and aspherical intraocular lenses (IOLs) by measuring higher-order aberration and contrast sensitivity (CS) values.

Design: Prospective controlled study.Participants: Fifty-seven patients with age-related cataract (61 eyes).

Patients were randomly allocated to 1 of 3 groups and implanted with either aspherical IOLs, Acrysof IQ (SN60WF) or Tecnis Z9001, or a spherical IOL, Acrysof Natural. Patients underwent routine examinations, includ-ing visual acuity, slit-lamp checks, and best-corrected visual acuity (BCVA), as well as measurement of higher-order aberrations and CS values, preoperatively and at 1 week, 1 month, and 2 months postoperatively.

Results: All the patients had a BCVA better than 20/30 postoperatively. The spherical aberrations of the IQ group and Tecnis group were both lower than in the Natural (control) group (IQ: p < 0.05; Tecnis: p < 0.05); there was no significant difference in coma and higher-order aberration. No statistically significant difference was found in spherical aberration, coma, or higher-order aberration between the IQ and Tecnis groups. Under glare conditions, the CS values of the 2 aspherical IOLs were obviously better (IQ: p < 0.05; Tecnis: p < 0.05) than the CS value of the spherical IOL group at low frequency (IQ: 6.3 , Tecnis: 4.0 ); under non-glare conditions there was a significant difference in CS values between the aspherical IOL groups and the control group (IQ: p < 0.01; Tecnis: p < 0.01) at low frequency (both 6.3 ). There was no statistical difference between the IQ and the Tecnis groups with or without glare.

An aspherical IOL can effectively reduce spherical aberration after cataract surgery, enhance CS values, and improve visual quality compared with traditional spherical IOLs for age-related cataract. However, there was no statistically significant difference in postoperative aberration and CS values between the Acrysof IQ and Tecnis Z9001 aspherical IOLs.

Objet : Cette étude compare la performance visuelle des lentilles intraoculaires (LIO) sphériques et asphériques en mesurant l’aberration d’ordre supérieur et les valeurs de sensibilité au contraste (SC).

Nature : Étude prospective contrôlée.Participants : Cinquante-sept patients atteints de cataracte liée à l’âge (61 yeux).

: Les patients ont été répartis au hasard en trois groupes et ont reçu des implants de LIO asphériques, soit Acrysof IQ (SN60WF) ou Tecnis Z9001, ou sphérique, Acrysof Naturel. Ils ont subi des examens de routine, notamment acuité visuelle, vérification à la lampe à fente, meilleure acuité visuelle après correction (MAVC) et mesure des aberrations d’ordre supérieur et des valeurs SC, avant l’opération, 1 semaine, 1 et 2 mois après.

: Tous les patients avaient une MAVC supérieure à 20/30 après l’opération. Les aberrations sphériques du groupe IQ et du groupe Tecnis étaient inférieures à celles du groupe (témoin) Naturel (IQ : p < 0,05; Tecnis : p < 0,05); il n’y avait pas d’écart significatif d’aberration de la coma et d’ordre supérieur. On n’a constaté aucun écart significatif d’aberration sphérique ni d’aberration de la coma ou d’ordre supérieur entre les groupes IQ et Tecnis. Sous éblouissement, les valeurs SC des 2 LIO asphériques étaient évidemment supérieures (IQ : p < 0,05; Tecnis : p < 0,05) à la valeur SC du groupe avec LIO sphérique à basse fréquence (IQ : 6,3, Tecnis : 4,0); sans éblouissement, il y avait un écart significatif des valeurs SC entre les groupes de LIO asphérique et le groupe té-moin (IQ : p < 0,01; Tecnis : p < 0,01) à basse fréquence (tous deux, 6,3). Il n’y avait pas d’écart statistique entre les groupes IQ et Tecnis avec ou sans éblouissement.

: Les LIO asphériques peuvent effectivement réduire l’aberration sphérique après la chirurgie de la cataracte, augmenter les valeurs SC et améliorer la qualité visuelle comparativement aux LIO sphériques tradition-nelles pour la cataracte liée à l’âge. Il n’y a cependant pas d’écart statistiquement significatif d’aberration postopé-ratoire et de valeurs SC entre les LIO Acrysof IQ et Tecnis Z9001.

Increasing spherical aberration is one of the reasons for the decline in visual quality with age.1 During youth,

negative spherical aberration in the clear lens can compen-sate for corneal positive spherical aberration, but the nega-

tive spherical aberration of the lens is attenuated and even becomes positive as age increases. With the corneal positive spherical aberration, the total spherical aberration of the eye is increased.

From the Department of Ophthalmology, First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China

Originally received Jan. 25, 2008Accepted for publication June 5, 2008Published online Apr. 24, 2009

Correspondence to Dinghua Lou, Department of Ophthalmology, First Affiliated Hospital, College of Medicine, Zhejiang University, 79 Qingchun Rd., Hangzhou, Zhejiang, China; [email protected]

This article has been peer-reviewed. Cet article a été évalué par les pairs.

Can J Ophthalmol 2009;44:274–8doi:10.3129/i08-121

Spherical and aspherical intraocular lenses—Cui et al.

CAN J OPHTHALMOL—VOL. 44, NO. 3, 2009 275

According to a study of nuclear and cortical cataract by Kuroda et al.,2 patients with nuclear cataracts were shown to have negative and those with cortical cataracts to have positive spherical aberration. In the authors’ view, besides dispersion, intraocular aberration was the main reason for the decline in visual quality in mild nuclear and cortical cataracts. Fujikado et al.3 came to similar conclusions. Therefore, aberration assessment has become an import-ant means of evaluating visual quality and function for cataract patients.4

The techniques used in modern cataract surgery and intraocular lens (IOL) implantation have reached matur-ity. The materials and designs have become increasingly advanced, and a growing number of patients have received cataract surgery in pursuit of better visual quality as well as reconstruction of visual acuity.

Aspherical IOLs can be designed to improve image qual-ity by minimizing dispersion and improve visual function by reducing spherical aberration. Two aspherical IOLs were chosen for this research: Acrysof IQ (SN60WF) (Alcon Inc, Fort Worth, Tex.), which provides aspherical surface modification on the posterior surface, and Tecnis Z9001 (AMO Inc, Santa Ana, Calif.), which is on the anterior surface; the spherical IOL Acrysof Natural (SN60AT) (Alcon Inc) was chosen as the lens for the control group. The visual quality of spherical and aspherical IOLs was evaluated by comparing the postoperative aberration and contrast sensitivity (CS).

METHODS

PatientsThis prospective study followed the guidelines of the

Declaration of Helsinki, and written informed consent was obtained from each patient. Institutional Review Board ap-proval was obtained. Patients were included who had age-related cataract, underwent bilateral cataract surgery at the First Affiliated Hospital, Zhejiang University, ranged in age from 50–80 years, and had low degrees of spherical di-opters ( 2.5 D) and astigmatism ( 1.0 D cylindrical) postoperatively. Exclusion criteria were a history of ocular diseases, such as corneal disease, glaucoma, uveitis, and ret-inal detachment, and systemic diseases, such as diabetes and hyperthyroidism. After signing an informed consent state-ment, patients were randomly allocated to 1 of 3 groups to receive the Acrysof IQ (SN60WF), Tecnis Z9001, or Acrysof Natural IOL. Each patient underwent a preopera-tive routine cataract examination, including visual acuity, corneal endothelium cell count, ocular electrophysiology, type-A and type-B ultrasonography, and eye anterior seg-ment and slit-lamp examinations.

Surgical techniqueAll surgeries were performed by the same surgeon. Fol-

lowing dilation of the pupil, retrobulbar nerve block anes-thesia was used. A temporal clear cornea tunnel incision

with a width of 3 mm and length of 1.5 mm was made with a diamond knife. After a viscoelastics injection into the anterior chamber, 5.0 mm to 5.5 mm central continuous curvilinear capsulorhexis and hydrodissection were applied. Then phacoemulsification (Legacy 20000, Alcon Inc) was performed, and the lens nucleus was removed. After elim-ination of residual cortex, viscoelastic was injected into the anterior chamber, and intracapsule implantation of the IOL was performed. Finally, the viscoelastics in the anter-ior chamber were removed by the pinhead and watertight corneal incision.

All the operations were uneventful. After the operation, 20 mg gentamicin and 2 mg dexamethasone were injected subconjunctivally. Postoperatively, the eyes were treated with 0.3% ofloxacin and 0.1% fluorometholone eye drops; dexamethasone tablets were taken orally.

Postoperative examinationsThe follow-up examinations were scheduled at 1 week,

1 month, and 2 months after surgery. Visual acuity, best-corrected visual acuity (BCVA), refraction, intraocular aberration (OPD-Scan and ARK-10000, Nidek Inc, Fre-mont, Calif.), and CS (CSV-1000, VectorVision, Green-ville, Ohio) were re-examined at the 2-month follow-up. The sixth order higher-order aberration was measured. Higher-order aberration, spherical aberration, and the value of coma root mean square (RMS), measured at 5 mm pupil diameter, were analyzed and compared among the 3 groups. Parameters of CS were set at a duration of 0.4 seconds and intervals of 1 second. Best spectacle corrective CS was measured under non-glare and glare conditions. Wavefront aberration and CS were checked by the same surgeon.

Statistical analysisThe statistical analysis was performed using the Statis-

tical Package for the Social Sciences, version 12.0 (SPSS Inc, Chicago, Ill.). The data were analyzed using t tests and

2 tests.

RESULTS

Fifty-seven patients (61 eyes) participated, of whom 20 patients (21 eyes) were in the IQ group, 18 patients (20 eyes) in the Tecnis group, and 19 patients (20 eyes) in the Natural group. Excluded were those cases who were un-able to understand or cooperate with the CS examination or were lost to follow-up. There was no significant differ-ence in age, sex, laterality, or diopter of the IOLs among the 3 groups. Postoperative BCVA of all patients was 20/30 or better, and there were no statistically significant differences among the 3 groups (Table 1).

No operative or postoperative complications had oc-curred in any patient at the 2-month follow-up. No case of IOL eccentricity or displacement was observed by slit-lamp examination.

The RMS of high-order aberration was measured with the



pupil at 5 mm diameter 2 months postoperatively. In the IQ group, the high-order aberration was 0.38 m (SD 0.15 mm), spherical aberration was 0.06 m (SD 0.04 mm), and coma was 0.14 m (SD 0.09 m); in the Tecnis group, the high-order aberration was 0.43 m (SD 0.18 m), spher-ical aberration was 0.07 m (SD 0.03 m), and coma was 0.15 m (SD 0.07 m); and in the Natural group, the values were 0.42 m (SD 0.16 m), 0.12 m (SD 0.06 m), and 0.19 m (SD 0.14 m). Comparing the IQ group and Tec-nis group with the Natural group, the spherical aberrations of the first 2 groups were significantly lower than that of the control group (IQ group: p < 0.05,Tecnis group: p < 0.05). Hence, there were obvious differences between the control group and the other 2 groups in spherical aberration, but not in high-order aberration and coma. No statistically sig-nificant difference was found between the 2 aspherical IOL groups in any aspects (Table 2).

At 2 months postoperatively, best spectacle corrective CS was measured with and without glare. Under non-glare condition, the CS of the IQ group was significantly bet-ter than that of the Natural group (p < 0.05) at a visual angle of 6.3 (low frequency), but there was no difference at other angles (spatial frequency). The CS of the Tecnis group was significantly better than that of the control group (p < 0.05) at a visual angle of 4.0 but again there was no difference at other angles. No statistically significant differ-ence was found between the IQ and Tecnis groups at any visual angle.

Under glare conditions, the CS in both aspherical groups was significantly better than in the control group at a vis-ual angle of 6.3 (low frequency) (IQ: p < 0.01, Tecnis:

p < 0.01), but there was no difference at any other angle. No statistical difference was found between the IQ and Tecnis groups (Tables 3 and 4; Figs. 1 and 2).

CONCLUSIONS

The continued development of the wavefront aberration technique within the various branches of clinical ophthal-mology has had a far-reaching impact on corneal refract-ive surgery, contact lenses, intraocular lens design, and the post operative check of refractive surgery. The wavefront aberration technique quantifies low- and high-order aber-rations in the visual system. High-order aberration, such as spherical aberration and coma, may influence the quality of the intraocular image.

With the development of wavefront aberration tech-niques, in the design of IOLs an attempt has been made to mirror natural crystal as closely as possible. Traditional single-piece plane-convex or dual-convex IOLs can result in positive spherical aberration and are unable to offset cor-neal positive spherical aberration, ultimately leading to a decline in image quality. Some patients have complained about glare, halo, and night vision disturbances after IOL implantation, which can be attributed to spherical aberra-tion.5 Aspherical IOLs can compensate for corneal positive spherical aberration and reduce spherical aberration after cataract surgery.6,7 Our clinical trial involved a compara-tive study of 2 types of aspherical IOLs (Acrysof IQ and TecnisZ9001), which can correct corneal positive spherical aberration through aberration technique, and a spherical IOL (Acrysof Natural) as a control lens.

Table 1—Demographic and clinical data on 3 groups undergoing IOL implantation

Measure IQ group Tecnis group Natural group

Sex,* n Male 11 9 10 Female 9 9 9Age,† y (SD) 70.2 (6.7) 67.3 (9.3) 67.8 (7.6)Eyes,* n OD 11 10 11 OS 10 10 9Diopter of IOL† (SD) 20.9 (1.8) 21.0 (1.3) 20.2 (2.4)Postoperative BCVA* 20/25 14 16 14 20/30 7 4 6

*p > 0.5 by 2 test.†p > 0.5 by t test comparison between each set of 2 groups.Note: IOL, intraocular lens; BCVA, best-corrected visual acuity.

Table 2—Higher-order aberration after spherical and aspherical IOL implantation

GroupHigher-order aberration,

RMS (SD)Spherical aberration,

RMS (SD) Coma, RMS (SD)

IQ 0.38 (0.15) 0.06 (0.04)* 0.14 (0.09)Tecnis 0.43 (0.18) 0.07 (0.03)† 0.15 (0.07)Natural 0.42 (0.16) 0.12 (0.06) 0.19 (0.14)*Comparison between IQ and Natural groups, p < 0.05. †Comparison between Tecnis and Natural groups, p < 0.05.Note: IOL, intraocular lens; RMS, root mean square.

Table 3—Contrast sensitivity values after spherical and aspherical IOL implantation (under non-glare conditions)

CS, log value (SD)

Spatial frequency, degrees IQ group* Tecnis group† Natural group

6.3 1.69 (0.15) 1.66 (0.21) 1.54 (0.33)4.0 1.55 (0.16) 1.63 (0.19) 1.46 (0.28)2.5 1.31 (0.18) 1.30 (0.30) 1.28 (0.31)1.6 1.09 (0.18) 1.00 (0.29) 1.01 (0.28)1.0 0.69 (0.18) 0.69 (0.24) 0.68 (0.25)0.7 0.38 (0.18) 0.35 (0.12) 0.29 (0.20)*Comparison between IQ and Natural groups, p < 0.05.†Comparison between Tecnis and Natural groups, p < 0.05.Note: IOL, intraocular lens; CS, contrast sensitivity.

Table 4—Contrast sensitivity values after spherical and aspherical IOL implantation (under glare conditions)

CS, log value (SD)

Spatial frequency, degrees IQ group* Tecnis group† Natural group

6.3 1.50 (0.13) 1.54 (0.27) 1.34 (0.17)4.0 1.33 (0.19) 1.34 (0.31) 1.21 (0.26)2.5 1.11 (0.18) 1.11 (0.26) 1.11 (0.23)1.6 0.86 (0.18) 0.89 (0.25) 0.79 (0.26)1.0 0.52 (0.14) 0.52 (0.16) 0.54 (0.12)0.7 0.30 (0.12) 0.30 (0.14) 0.21 (0.19)*Comparison between IQ and Natural groups, p < 0.05.†Comparison between Tecnis and Natural groups, p < 0.05.Note: IOL, intraocular lens; CS, contrast sensitivity.


CAN J OPHTHALMOL—VOL. 44, NO. 3, 2009 277

Theoretically, the Acrysof IQ IOL has posterior surface aspherical modification and –0.2 m spherical aberration itself. Total intraocular spherical aberration reached +0.1 m after implantation, which was similar to normal values

found in young people. The Tecnis IOL has anterior surface aspherical modification and –0.27 m spherical aberration itself. Total spherical aberration came to 0. The Acrysof Natural IOL has positive spherical aberration itself.

Research on IQ and Natural IOLs by Rocha et al.8 has indicated that the spherical aberration, as well as total aber-ration and high-order aberration, of the IQ group was significantly lower than that of the Natural group. How-ever, there was no obvious difference in coma between the 2 groups. This was similar to the results of our research. In our study, the intraocular spherical aberration of the IQ group was 0.06 m (SD 0.04 m) and significantly lower than that of the Natural group at 5 mm pupil diameter (p < 0.05). However, there was no statistically significant difference in high-order aberration or coma between the 2 groups.

Many studies have verified that with a Tecnis IOL, intra-ocular spherical aberration decreased more than with a spherical IOL, but no statistical difference in coma has been found.9–11 In our study, intraocular spherical aberration in the Tecnis group was 0.07 (SD 0.03 m) and significantly

lower than in the Natural group (p < 0.05); there was no statistically significant difference in high-order aberration and coma between the 2 groups.

All these findings show that aspherical modified IOLs can better and more effectively reduce intraocular spher-ical aberration and total aberration than spherical IOLs, no matter whether they involve anterior or posterior surface modification; they can effectively compensate for corneal positive spherical aberration and reduce total intraocular aberration after cataract surgery. However, there has been no comparison of intraocular aberration between the two types of aspherical IOL, Acrysof IQ and Tecnis Z9001, in published articles as yet. Our research showed that there was no statistically significant difference between the IQ and Tecnis groups in high-order aberration, spherical aber-ration, or coma. Therefore, in our view, there was no ob-vious difference in the total aberration of the two aspherical IOLs after implantation, despite their different spherical aberration in the laboratory model design.

Our results showed no significant difference in BVCA among the 3 groups at 2 months postoperatively. However, there was little correlation between the objective measure-ment of visual acuity and subjective distance visual acuity.12 In that regard, more and more researchers are evaluating visual quality with the use of CS after cataract surgery. The research by Rocha et al.8 has shown that the CS of the IQ group was obviously better than that of the Natural group under conditions of moderate luminance and low frequency. Denoyer et al.13 found that aspherical IOLs can improve CS under conditions of moderate luminance and high frequency. The same result was found by Bellucci et al.14 as well. Other researchers have also indicated that there was no significant difference in CS between aspherical and spherical IOLs, although aspherical IOLs can effectively re-duce postoperative aberration.9,10,15 In our study, the CS of the aspherical IOL groups was obviously better than that of the spherical IOL group (control group) at a low frequency (IQ: 6.3 , Tecnis: 4.0 ) without glare; with glare, there was also a significantly better CS in the aspherical IOL groups than the control group at low frequency (both 6.3 ).

IOL tilting and decentration, which result in asymmetric high-order aberration, lead mainly to coma and secondary astigmatism. Some research has suggested that aspherical IOL tilting and decentration is more harmful than spher-ical tilting and decentration.16,17 Taketani et al.18 discovered from in vitro experiments that the aspherical IOL must be placed in the range of 0.4 mm away from the optic axis, and the tilted angle must be less than 7 in order to obtain bet-ter visual quality than normal; IOL tilting mostly caused an increase in intraocular coma. From the 1980s to the 1990s, the development of aspherical IOLs was hampered because of decentration of the IOL, which resulted in visual acuity worse than that of spherical IOLs.19 However, this problem seemed to be solved after development of the technique of phacoemulsification, continuous capsulorhexis, and im-plantation of foldable IOLs. Taketani et al.18 verified that

Fig. 1—Contrast sensitivity (CS) under non-glare conditions after spherical and aspherical intraoc-ular lens implantation.

Fig. 2—Contrast sensitivity (CS) under glare con-ditions after spherical and aspherical intraocular lens implantation.



after phacoemulsification and intracapsule IOL implanta-tion, the IOL was located stably 12 months postoperatively regardless of materials and edge design. A comparison of the Tecnis Z9000 IOL, CeeOn 911 IOL, and Natural lens by Bellucci et al.11 showed that there was no significant dif-ference in total coma among these 3 groups. Hence, the ad-vantage of aspherical IOL should not be negated because of the possibility of IOL decentration. In our research, no case of IOL tilting and decentration was found under slit-lamp observation at 2 months postoperatively. In addition, there was no statistical difference in coma among the 3 groups.

In conclusion, aspherical IOL implantation can effect-ively compensate for corneal positive spherical aberration, enhance contrast sensitivity, and improve visual quality compared with traditional spherical IOL after cataract ex-traction by phacoemulsification. However, there was no sta-tistically significant difference in postoperative aberration and CS between the Acrysof IQ and Tecnis Z9001 aspher-ical IOLs.

The authors have no proprietary or commercial interest in any materials discussed in this article.

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Keywords: aspherical intraocular lens, wavefront aberration, con-trast sensitivity, age-related cataract

comparison of pseudophakic visual quality in spherical and aspherical intraocular lenses

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