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Clinical Study
Effect of Spherical Aberration on the Optical Quality after
Implantation of Two Different Aspherical Intraocular Lenses
Michael Lasta,
1,2
Kata Miháltz,
1,2
Illés Kovács,
3
and Pia Veronika Vécsei-Marlovits
1,2
1
Department of Ophthalmology, Hospital Hietzing, Vienna, Austria
2
Karl Landsteiner Institute of Process Optimization and QM in Cataract Surgery, Vienna, Austria
3
Department of Ophthalmology, Semmelweis University, Budapest, Hungary
Correspondence should be addressed to Kata Miháltz; kata.mihaltz@wienkav.at
Received 26 February 2017; Revised 21 May 2017; Accepted 12 June 2017; Published 16 August 2017
Academic Editor: Tamer A. Macky
Copyright © 2017 Michael Lasta et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Purpose. To compare the effect of spherical aberration on optical quality in eyes with two different aspherical intraocular lenses.
Methods. 120 eyes of 60 patients underwent phacoemulsification. In patients’eyes, an aberration-free IOL (Aspira-aA; Human
Optics) or an aberration-correcting aspherical IOL (Tecnis ZCB00; Abott Medical Optics) was randomly implanted. After
surgery, contrast sensitivity and wavefront measurements as well as tilt and decentration measurements were performed. Results.
Contrast sensitivity was significantly higher in eyes with Aspira lens under mesopic conditions with 12 cycles per degree (CPD)
and under photopic conditions with 18 CPD (p=002). Wavefront measurements showed a higher total spherical aberration
with a minimal pupil size of 4 mm in the Aspira group (0.05 ±0.03) than in the Tecnis group (0.03 ±0.02) (p=0001). Strehl
ratio was higher in eyes with Tecnis (0.28 ±0.17) with a minimal pupil size larger than 5 mm than that with Aspira (0.16
±0.14) (p=004). In pupils with a minimum diameter of 4 mm spherical aberration had a significant effect on Strehl ratio, but
not in pupils with a diameter less than 4 mm. Conclusions. Optical quality was better in eyes with the aberration-correcting
Tecnis IOL when pupils were large. In contrast, this could not be shown in eyes with pupils under 4 mm or larger. This trial is
registered with Clinicaltrials.gov NCT03224728.
1. Introduction
In recent years, cataract surgery has become a highly precise
and safe surgical procedure due to phacoemulsification tech-
nique and advanced intraocular lens (IOL) designs. To face
increasing demands on visual and refractive outcome, efforts
have been made to further improve IOL designs. Today, it is
widely recognized that implantation of spherical IOLs leads
to increased spherical aberrations (SA), therefore decreasing
retinal image quality [1]. Aspherical IOLs have been devel-
oped in order to overcome this issue. Aberration-correcting
aspherical IOLs are aiming to compensate for the corneal
spherical aberration of the eye. It is known that aspherical
lenses significantly decrease higher-order aberrations (HOA)
postoperatively [1]. A number of studies have shown that
aspherical IOLs perform better compared to conventional
spherical ones in terms of contrast sensitivity (CS), particu-
larly under mesopic conditions [2, 3]. Furthermore it is
known that a precise position of an aspherical IOL is essen-
tial for perfect optical quality [4]. IOL displacement such as
tilt and decentration could not only impair its aberration-
correcting effect but may even induce additional optical
aberrations [4, 5].
The question whether correction of the total SA of the eye
or some residual SA leads to better visual outcome and better
optical quality remains to be elucidated. It is known that
healthy young eyes with good visual acuity have some posi-
tive ocular SA [6]. However, results of other studies indicate
that a postoperative SA of zero should be aimed in order to
optimize visual outcome [3, 7].
Aberration-free aspherical IOLs follow another concept
of aspherical IOL design. These implants have no inherent
Hindawi
Journal of Ophthalmology
Volume 2017, Article ID 8039719, 6 pages
https://doi.org/10.1155/2017/8039719
SA; thus, they do not introduce additional SA into the
optical system of the eye. Some studies indicate that
aberration-free aspheric IOLs may result in better optical
quality compared to aberration-correcting aspheric IOL-
s—even in case of decentration and tilt of the IOL [8].
Our study aimed to evaluate the optical quality and poten-
tial benefits on visual outcome of an aberration-free
aspherical IOL compared to those of an aspherical IOL
with negative SA.
Optical quality is a subjective construct that can only be
described indirectly by objective metrics such as wavefront
error measurements and visual quality metrics or functional
data like visual acuity and contrast sensitivity. Wavefront
analysis isolates the effect of lower-order aberrations (defo-
cus and astigmatism) and higher-order aberrations as well
as the contribution of individual aberrations on optical qual-
ity. Modulation transfer function (MTF) and Strehl ratio are
well related to the image quality of an optical system, includ-
ing the human eye [9].
In this study, an aberration-free aspherical IOL (Aspira-
aA, Human Optics AG; Erlangen, Germany) was compared
to an aberration-correcting aspherical IOL with negative SA
(Tecnis ZCB00, Abbott Medical Optics; Illinois, USA)
regarding the effect of spherical aberration on visual outcome
and optical quality.
2. Methods and Subjects
This prospective single-center study was conducted at the
Department of Ophthalmology, Hospital Hietzing, Vienna,
Austria, in accordance with the Declaration of Helsinki.
The study received approval from the Ethics Committee of
the City of Vienna, and each subject gave written informed
consent before taking part.
Before inclusion, all patients underwent a full ophthalmic
assessment including slit lamp examination and funduscopy.
Intraocular eye pressure was measured with the Goldmann
applanation tonometry. Optical biometry was performed
using the IOLMaster 500 (Carl Zeiss Meditec AG; Jena,
Germany) for axial length and corneal radii of curvature
measurements. For IOL calculation, SRK®/T, Holladay I,
and Hoffer® Q were used, depending on the length of the
patients’eyes.
Patients with bilateral age-related cataract and an age
range between 50 and 80 years were included. Eyes with
relevant other ocular pathologies or previous surgeries, a
potential postoperative corrected distance visual acuity
worse than 20/20, and corneal astigmatism of 1.5 diopters
and more were excluded from the study. For patients’subjec-
tive refraction, a plus cylinder design was used. To be able to
compare IOL function, patients had to manifest similar
corneal asphericity.
37 female and 23 male subjects were enrolled in this trial.
They were randomly assigned to implantation of the
aberration-free aspherical Aspira-aA in one eye and the
aberration-correcting aspherical Tecnis ZCB00 in the fellow
eye. Both IOLs are monofocal acrylic one-piece lenses with
C-loop haptic design.
The eye with the worse visual acuity was operated first,
followed by the second eye one week afterwards. All of our
patients have been corrected for emmetropy after surgery.
2.1. Surgical Technique. Surgery was performed in topical
anesthesia using oxybuprocaine eye drops. The self-sealing
2.4 mm incision, capsulorrhexis, phacoemulsification, irriga-
tion and aspiration of cortical material, and injection of
viscoelastic substance into the capsular bag were performed
as standard procedures. The IOL was implanted via an injector
into the capsular bag followed by thorough aspiration of the
viscoelastic substance from the eye.
2.2. Postoperative Assessments. Three months postopera-
tively, the following measurements were carried out in
each subject:
Uncorrected distance visual acuity (UDVA) and cor-
rected distance visual acuity (CDVA) were measured using
the ETDRS chart at a viewing distance of four meters. In
addition, monocular defocus curve measurements were per-
formed with the best distance correction adding glasses in
0.50-diopter increments from +0.5 D to −3.00 diopters.
Photopic and mesopic contrast sensitivity was evaluated
with best refraction using the Optec 6500 contrast sensitivity
tester (Stereo Optical Co.; Chicago, Illinois, USA) under
photopic (85 cd/m
2
) and mesopic (3 cd/m
2
) conditions. This
item uses functional acuity contrast charts (FACT) testing
five spatial frequencies and nine levels of contrast. The
patient determines the last grating seen for each row (A, B,
C, D, and E) and reports the orientation of the grating: right,
up, or left. The last correct grating seen for each spatial
frequency is plotted on a contrast sensitivity curve.
Thereafter, pupils were dilated using one eye drop
containing 0.5% tropicamide and one eye drop containing
10% phenylephrine.
To assess optical quality characteristics including higher-
order aberrations, wavefront measurements were obtained
using the HOYA iTrace™Surgical Workstation (HOYA
Surgical Optics GmbH; Frankfurt, Germany).
The HOYA iTrace Surgical Workstation provides an
objective clinical evaluation of the eye’s optical quality.
Performing these measurements with maximum-dilated
pupils, we calculated all relevant parameters with a pupil size
of two, three, four, and five millimeters.
The following parameters have been calculated:
Wavefront aberrometry describes the optical properties
of the eye in individual Zernike polynomials. Optical quality
can be described by metrics of image quality for point objects
(point spread function (PSF)) and for grating objects (modu-
lation transfer function (MTF)). The iTrace is able to
measure the following image quality metrics: PSF, Strehl
ratio, and MTF.
Strehl ratio is the ratio of the peak height of the PSF
divided by the maximum intensity of PSF in the diffraction-
limited perfect eye. Strehl ratio ranges from 0 to 1; the greater
Strehl ratio, the better the quality of vision [10]. By the
iTrace, Strehl ratio is calculated from the retinal PSF. The
MTF is the modulus of the Fourier transform of the PSF. It
2 Journal of Ophthalmology
characterizes the degradation of the image for every spatial
frequency of the object.
Root mean square (RMS) error was calculated by the
iTrace software from Zernike coefficients. The total HO
(higher order) is the RMS of higher-order terms (Z3 to Z6).
IOL tilt and decentration were measured with the Visante
anterior segment OCT (Carl Zeiss Meditec AG; Jena,
Germany). Images were obtained in mesopic conditions for
each examination. Anterior single-scan mode was used to
assess pictures. These were obtained in four axes (180 to 0
degrees, 45 to 225 degrees, 315 to 135 degrees, and 270 to
90 degrees). Tilt and decentration of IOLs were calculated
accordingly as previously described by Rosales et al. [11].
2.3. Statistical Analysis. Statistical analyses were performed
with Statistica 12.0 (Statsoft Inc.; Tulsa, OK, USA). The
Shapiro-Wilk Wtest was used to confirm normal distribu-
tion of the variables. Paired-samples t-test was used to
compare means between the eyes of the same subject. This
test allows for comparing within-subject parameters (visual
acuity, keratometric, OCT, and intraocular optical quality
parameters) in the two study groups by taking into
account between-eye correlations by treating data from
the two eyes of the same patient in statistical analyses as
repeated measures.
To determine the effect of intraocular spherical aberra-
tion on visual quality in relation to the pupillary diameter,
multivariable regression analysis using the generalized esti-
mating equation (GEE) model was performed where data
from patients who had measurements in both eyes were sta-
tistically analyzed as repeated measures. The type of the IOL
and corneal spherical aberration were included as con-
founders in these multivariable regression models to adjust
for their effect on total ocular Strehl ratio. Model fit was
assessed using the value of the corrected quasilikelihood
under independence model criterion (QICC) with a lower
QICC values indicating a better fit to data. In all analyses, a
pvalue less than 0.05 was considered statistically significant.
3. Results
The age range of the included patients was between 47 and 79
years (mean 69 ±7.8 years). For the three-month follow-up,
data of 47 persons were eligible for evaluation.
Preoperative findings of the patients are shown in Table 1.
Three months after phacoemulsification, mean corrected
distance visual acuity (CDVA) increased in all patients
(logMAR 0.073 ±0.092 in eyes with Aspira and 0.040 ±0.098
in eyes with Tecnis. There was no significant difference
between both IOL groups (p=0 22).
In all patients, postoperative refraction showed a slight
myopic shift. The difference between planned and manifest
postoperative sphere was found in a majority of the eyes;
however, we could not find a significant difference between
both lenses.
In addition, we measured no significant difference in
depth of focus between Aspira and Tecnis IOLs.
Postoperative characteristics are shown in Table 2.
3.1. Contrast Sensitivity. In eyes with the aberration-free
Aspira, higher contrast sensitivity under photopic as well as
under mesopic conditions was measured compared to that
in eyes with Tecnis IOL. However, only one out of 5 measure-
ments under photopic conditions with 18 cycles per degree
(CPD) as well as one measurement under mesopic condi-
tions with 12 CPD presented a significant difference between
both IOLs (Table 3).
3.2. Tilt and Decentration. Three months after implantation,
both IOLs showed a slight tendency to decentration in tem-
poral direction; however, no significant difference between
lenses was found (Table 4).
Vertical tilt was higher in Aspira than in Tecnis IOL.
However, this finding did not reach the level of significance.
Table 1: Patients’preoperative characteristics (mean ±SD; n=60).
Aspira-aA Tecnis ZCB00 pvalue
CDVA (logMAR) 0.38 ±0.13 0.39 ±0.14 0.85
Sphere (D) −0.50 ±2.32 −0.42 ±2.63 0.43
Cylinder (D) 0.68 ±0.61 0.74 ±0.5 0.40
Axial eye length (mm) 23.40 ±0.99 23.45 ±1.05 0.87
CDVA: corrected distance visual acuity.
Table 2: Patients’postoperative characteristics (mean ±SD; n=60).
Aspira-aA Tecnis ZCB00 pvalue
UDVA (logMAR) 0.14 ±0.13 0.12 ±0.15 0.25
CDVA (logMAR) 0.07 ±0.09 0.04 ±0.09 0.22
Sphere Δ(D) −0.22 ±0.67 −0.50 ±0.52 0.29
Depth of focus (D) 0.61 ±0.33 0.65 ±0.29 0.74
Corneal asphericity with
a pupil size of 4 mm 0.19 ±0.24 0.26 ±0.16 0.19
UDVA: uncorrected distance visual acuity; CDVA: corrected distance
visual acuity; sphere Δ:difference between scheduled and manifest
postoperative sphere.
Table 3: Contrast sensitivity values in the eyes, implanted with
Aspira or Tecnis IOLs. p: Student’st-test on dependent samples
(log; mean ±SD; n=60).
Aspira-aA Tecnis ZCB00 pvalue
Photopic
CPD 1.5 1.54 ±0.20 1.52 ±0.17 0.62
CPD 3 1.78 ±0.20 1.76 ±0.18 0.60
CPD 6 1.72 ±0.27 1.74 ±0.20 0.77
CPD 12 1.27 ±0.49 1.29 ±0.39 0.85
CPD 18 0.52 ±0.51 0.36 ±0.41 0.02
Mesopic
CPD 1.5 1.60 ±0.22 1.60 ±0.20 0.92
CPD 3 1.73 ±0.23 1.69 ±0.24 0.40
CPD 6 1.36 ±0.64 1.49 ±0.33 0.22
CPD 12 0.71 ±0.61 0.48 ±0.58 0.02
CPD 18 0.09 ±0.13 0.16 ±0.09 0.19
CDP: cycles per degree.
3Journal of Ophthalmology
In contrast, horizontal tilt was significantly lower in Aspira
compared to Tecnis (0.35 ±1.65
°
and 0.67 ±1.42
°
, resp.;
p=002; Table 4).
3.3. Wavefront Measurements. All wavefront measurements
were performed with a pupil diameter of 5 mm. Data with
a pupil size of 2, 3, and 4 mm were calculated with the
software program.
Higher-order root mean square (HORMS) showed no
significant difference between the two lenses. From 0.054
±0.042 in Aspira and 0.050 ±0.036 in Tecnis with a pupil size
of 2 mm, values increased to 0.52 ±0.25 and 0.56 ±0.52 with a
maximum-dilated pupil.
In contrast, total spherical aberration (TSA) was signif-
icantly higher in Aspira compared to Tecnis. However,
this was only shown with pupil sizes of minimum 4 mm
(p=0001; Table 5).
Total Strehl ratio was comparable in both lenses with a
pupil size of 2, 3, and 4 mm. However, with a pupil size of
5 mm, we calculated significantly higher values in eyes with
Tecnis IOL than in eyes with Aspira IOL (0.16 ±0.14 versus
0.08 ±0.17, resp.; p=004). This effect was shown in modula-
tion transfer function as well (0.46 ±0.13 versus 0.39 ±0.15;
p=004). However, these differences did not reach the level
of significance after a Bonferroni correction.
Multivariate regression models showed that total spheri-
cal aberration had a significant negative effect (beta: −1.54,
95% CL: −2.56 to −0.51; p=0004) on total ocular Strehl ratio
when the pupillary diameter was ≥4 mm, but not when pupil-
lary diameter was less than 4 mm after adjustment for the
effect of IOL type and corneal spherical aberration.
4. Discussion
The surgical technique of phacoemulsification has been
improved continuously. The measure of successful surgery
is more than just an increased visual quality. Patients expect
high optical quality without disturbing aberrations as well as
high contrast sensitivity during night and day.
A various number of spherical and aspherical IOL
designs have been developed aiming to achieve perfect
optical quality.
In this trial we compared the aberration-free aspher-
ical Aspira-aA with the aberration-correcting aspherical
Tecnis ZCB00.
Several authors mentioned that there is increased opti-
cal quality and subjective satisfaction in patients with
aspherical lenses compared to those with spherical ones
[12, 13]. In the clinical trial of Santhiago et al. [12], the
aspherical aberration-free Akreos AO was compared with
spherical Akreos Fit. The authors described significantly
higher contrast sensitivity and decreased aberrations in the
aspherical lens.
Apart from comparisons between spherical and aspheri-
cal IOLs, a few authors compared different aspherical lenses
with each other.
In the work of Rajabi et al. [14], the Aspira-aA was
compared with Akreos AO. In contrast to our findings, they
mentioned that there was no significant difference in higher-
order aberrations between the two lenses. Due to the fact
that they compared two IOLs with similar SA, the major
question (what is the ideal SA regarding optical quality)
could not be answered.
Johansson et al. [15] evaluated Akreos AO and Tecnis
Z9000. Although the Tecnis showed less aberration than
the Akreos, more patients reported better subjective quality
with Akreos IOL. The same IOLs were evaluated in the work
of Baghi et al. [16]. In this trial, Akreos AO causes signifi-
cantly more spherical aberration in pupil diameter of 4 and
6 mm. This seems to be in accordance with our findings,
where Aspira lens causes higher spherical aberrations in
pupil diameters of 4 and 5 mm.
Nochez and coworkers [17] stated that an IOL with a
spherical aberration of zero leads to better optical quality
and even better MTF contrast than aberration-correcting
intraocular lens. However, the best compromise of subjective
depth of contrast and objective contrast sensitivity is reached
with a total spherical aberration between 0.07 μm and
0.10 μm. We found a total spherical aberration between
0.006 μm with a pupil size of 2 mm and 0.11 μm with a pupil
size of 5 mm.
In general a higher spherical aberration decreases Strehl
ratio resulting in lower optical quality [10]. We can reassure
this phenomenon as our multivariable regression models
showed that intraocular spherical aberration had significant
negative effect on total ocular Strehl ratio. Nevertheless, it
has to be mentioned that this effect applied only when the
pupillary diameter was 4 mm and more. With pupil sizes of
less than 4 mm, adjustment for the effect of IOL type and cor-
neal spherical aberration did not show this effect. We can
assume that spherical aberration influences Strehl ratio and
optical quality less when pupil sizes are small due to the fact
that small pupils present smaller values of spherical aberra-
tion. In contrast, higher spherical aberration significantly
influences optical quality when the pupils are small.
Results of evaluating contrast sensitivity between aspher-
ical lenses differ in various studies. Shentu et al. [18] could
not find any difference in contrast sensitivity between the
Table 4: Results of Visante OCT measurements (mean ±SD; n=60).
Aspira-aA Tecnis ZCB00 pvalue
Horizontal tilt (
°
) 0.35 ±1.65 0.67 ±1.42 0.02
Vertical tilt (
°
) 0.63 ±1.76 0.19 ±1.24 0.35
Horizontal decentration (mm) 0.03 ±0.16 0.04 ±0.27 0.94
Vertical decentration (mm) 0.08 ±0.15 0.07 ±0.23 0.96
Table 5: Total ocular higher-order spherical aberrations measured
at different pupillary diameters in eyes implanted with Aspira or
with Tecnis IOL (μm; mean ±SD; n=60).
Aspira-aA Tecnis ZCB00 pvalue
2 mm 0.006 ±0.004 0.006 ±0.005 0.88
3 mm 0.02 ±0.01 0.02 ±0.01 0.9
4 mm 0.05 ±0.03 0.03 ±0.02 0.001
5 mm 0.11 ±0.05 0.07 ±0.05 0.001
4 Journal of Ophthalmology
two aspherical lenses. Our results show significant differences
in contrast sensitivity, although this was found at 18 CPD
under photopic conditions and at 12 CPD under mesopic
conditions. Hence, it can be assumed that patients might
not notice any distinction in their daily life.
Jia and Li [19] mentioned that a presurgical measure-
ment of corneal spherical aberration should be performed
to determine which type of IOL would lead to optimal optical
quality. A possible solution for this problem would be to
choose the SA of the implanted IOL individually as suggested
by Jia and Li.
Tilt and decentration of IOLs may lead to higher spheri-
cal aberration resulting in decreased optical quality [20]. In
our study, three months postoperatively, a significantly
higher horizontal tilt of Tecnis lens was measured. In
contrast, both lenses did not differ in vertical tilt as well as
decentration, although a horizontal temporal decentration
were found in both eyes. These findings comply with the work
of Rosales et al. [11]. They described that IOL decentration
tends to be mirror symmetric between the right and left eye.
Study limitations are that only total aberrations of study
eyes were calculated. Further, in order to obtain precise
wavefront measurements, detailed knowledge about internal
aberrations would be essential, which will be subject of future
investigations. Nevertheless, we aimed to constitute the total
efficiency of pseudophakic eyes. Furthermore, we included
patients with similar corneal asphericity in order to compare
both IOLs. Regarding statistics, Bonferroni calculations may
have been more suitable concerning data calculations, which
is considered as a drawback of the current study.
4.1. Conclusion. We can conclude that aberration-free as well
as aberration-correcting aspherical intraocular lenses feature
high optical quality conditions. When pupils are large, eyes
with aberration-correcting Tecnis IOL showed higher modu-
lation transfer function and Strehl ratio values than eyes with
aberration-free Aspira lens. Nevertheless, it has to be clarified
that this significance is not shown after a Bonferroni correc-
tion. Moreover, this benefit could not be verified in eyes with
pupils under 4 mm.
Disclosure
This work has been presented as a poster at DOG annual
meeting, Berlin, October 2017.
Conflicts of Interest
The authors declare that they have no conflict of interest.
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6 Journal of Ophthalmology
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