ARTICLE
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In vivo subjective and objective
longitudinal chromatic aberration
in patients bilaterally implanted with
same design of hydrophobic and
hydrophilic intraocular lenses
Q3
Maria Vinas, MSc, Carlos Dorronsoro, PhD, Nuria Garz
on, OD, MSc,
Francisco Poyales, MD, Susana Marcos, PhD
PURPOSE: To measure the longitudinal chromatic aberration in vivo using psychophysical and
wavefront-sensing methods in patients bilaterally implanted with monofocal intraocular lenses
(IOLs) of similar aspheric design but different materials (hydrophobic, Podeye and hydrophilic,
Poday).
SETTING: Instituto de Optica, Consejo Superior de Investigaciones Cientificas, Madrid, Spain.
DESIGN: Prospective observational study.
METHODS: Measurements were performed with the use of psychophysical (480 to 700 nm) and
wavefront-sensing (480 to 950 nm) methods, using a custom-developed adaptive optics system.
Chromatic difference-of-focus curves were obtained from best-focus data at each wavelength,
and the longitudinal chromatic aberration was obtained from the slope of linear regressions to
those curves.
RESULTS: The longitudinal chromatic aberration from psychophysical measurements was 1.37 diopters (D) G 0.08 (standard deviation) (hydrophobic) and 1.21 G 0.08 D (hydrophilic); from
wavefront-sensing longitudinal chromatic aberration was 0.88 G 0.07 D and 0.73 G 0.09 D,
respectively. In 480 to 950 nm, longitudinal chromatic aberration was 1.27 G 0.09 D
(hydrophobic) and 1.02 G 0.13 D (hydrophilic). Longitudinal chromatic aberration was
consistently higher in eyes implanted with the hydrophobic than the hydrophilic IOL (a difference
of 0.16 and 0.15 D, respectively). Similarly to findings in young phakic eyes, longitudinal
chromatic aberration from the psychophysical method is consistently higher than from wavefrontsensing, by 0.48 D (35.41%) for the hydrophobic and 0.48 D (39.43%) for the hydrophilic.
CONCLUSION: This study provides estimates of the longitudinal chromatic aberration measured in a
wider spectral range than that in previous studies, using psychophysical and wavefront-sensing
measurements.
Financial Disclosure: No author has a financial or proprietary interest in any material or method
mentioned.
J Cataract Refract Surg 2015; -:-–- Q 2015 ASCRS and ESCRS
In natural conditions, with polychromatic light,
retinal image quality is affected both by monochromatic and chromatic aberrations of the ocular optics
and their interactions. Chromatic aberration in the
eye arises from the wavelength dependence of the
Q 2015 ASCRS and ESCRS
refractive index of the ocular media (chromatic
dispersion) affecting diffraction, scattering, and
aberrations.1–3 Chromatic dispersion causes short
wavelengths to focus in front of long wavelengths,
producing a chromatic difference of focus between
http://dx.doi.org/10.1016/j.jcrs.2015.11.009
Published by Elsevier Inc.
0886-3350
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CHROMATIC ABERRATION WITH BILATERAL HYDROPHOBIC AND HYDROPHILIC IOLS
the shorter and longer wavelengths known as longitudinal chromatic aberration.4 The interactions between
chromatic and monochromatic aberrations have
drawn attention, particularly as the magnitude and
pattern of either aberration can be altered when the
crystalline lens of the eye is replaced by an intraocular
lens (IOL). In phakic eyes, it has been shown that
monochromatic aberrations play a protective role
against chromatic aberrations.5,6 This opens the discussion of whether correction of both chromatic and
monochromatic aberrations are needed to improve visual performance.7
In phakic eyes, longitudinal chromatic aberration
has been widely studied, and it is fairly accepted
that it is rather constant across the population and
with age.8,9 However, the reported longitudinal
chromatic aberration varies across studies, probably
associated with differences in the measurement techniques, psychophysical4,9–14 and reflectometric,15–19
as well as the spectral range under test. In a recent
study,20 we presented longitudinal chromatic aberration measured in the same subjects using psychophysical and reflectometry techniques in a wide
spectral range (450 to 950 nm) with adaptive optics
control of the subjects' natural aberrations. The longitudinal chromatic aberration measured psychophysically was significantly higher than that from
reflectometry techniques (1.51 diopters [D] versus
1.00 D in the 480 to 700 nm range).
In recent years, monofocal IOL designs have
improved not only to restore transparency or to correct refractive errors (sphere and cylinder) but also
to reduce the spherical aberration of the eye.21–25
However, the replacement of the IOL also modifies
the chromatic dispersion properties of the eye, as
Submitted: January 16, 2015.
Final revision submitted: March 30, 2015.
Accepted: March 31, 2015.
From the Instituto de Optica
(Vinas, Dorronsoro, Marcos), Consejo
Superior de Investigaciones Cientıficas, and the Instituto de
Oftalmologıa Avanzada (Garzon, Poyales), Madrid, Spain.
Supported by PhysIOL, Liege, Belgium. European Research Council-2011-AdC 294099 to Dr. Marcos, Spanish Government grant
FIS2011-25637 to Dr. Marcos, Consejo Superior de Investigaciones Cientıficas Junta de Ampliacion de Estudios-Preprograms,
and Ministerio de Ciencia e Innovacion Formacion de Profesotado
Universitario predoctoral fellowship to Dr. Vinas.
Daniel Pascual and Daniel Cortes provided technical support.
Corresponding author: Maria Vinas, MSc, Instituto de Optica
s,
Consejo Superior de Investigaciones Cientıficas, Serrano 121,
28006, Madrid, Spain. E-mail: [email protected].
this is affected by the refractive index wavelength dependency of the IOL material. Therefore, the optical
performance of the pseudophakic in polychromatic
light will be determined by both the IOL design and
the IOL material.
The impact of the chromatic aberrations in the pseudophakic eye has been acknowledged.26–28 There are
even proposals for IOL (diffractive) designs aiming at
correcting the ocular longitudinal chromatic aberration.29,30 The dispersion properties of the IOL are
defined by the Abbe number (ranging in most of
designs from 35 to 60). The higher the Abbe number,
the lower the longitudinal chromatic aberration. Most
reports of longitudinal chromatic aberration and polychromatic optical quality in pseudophakic eyes are
based on computational predictions on eye models
and the IOL material Abbe number.26,30,31 There are
very few studies reporting in vivo measurements of longitudinal chromatic aberration of pseudophakic eyes.
Nagata et al.27 measured the longitudinal chromatic
aberration in vivo (500 to 650 nm) in pseudophakic
eyes implanted with poly(methyl methacrylate) and
acrylic IOLs, using a modified chromoretinoscopy system.32 Perez-Merino et al.33 reported monochromatic
aberrations measured at 2 wavelengths (532 nm and
785 nm) in 2 groups of pseudophakic eyes implanted
with 2 IOLs (Tecnis, Abbott Medical Optics, Inc. and
Acrysof IQ, Alcon Laboratories, Inc.) of different materials and found statistical differences between the
chromatic difference of focus with the 2 IOL types
(0.46 D and 0.75 D, respectively), consistent with the
Abbe number of the IOL materials. Siedlecki et al.34 presented the chromatic difference of focus in pseudophakic eyes implanted with 2 types of Acrysof IOLs
(IQ SN60WF, spherical asymmetric biconvex IOL and
the SA60AT, aspheric asymmetric biconvex IOL) Q1
measured at 470 nm, 525 nm, and 660 nm with the
use of an autorefractometer adapted to monochromatic
measurements of refraction.
In this study, we present in vivo longitudinal
chromatic aberration in pseudophakic patients
bilaterally implanted with monofocal aspheric
hydrophobic and hydrophilic IOLs. Measurements
were performed on patients using psychophysical
and wavefront-sensing methods on a customdeveloped adaptive optics platform, provided with
a super-continuum laser source, a psychophysical
channel, a Hartman-Shack wavefront sensor, and
an electromagnetic deformable mirror to allow
control of monochromatic natural aberrations. The
psychophysical longitudinal chromatic aberration
was obtained in the visible range (480 to 700 nm)
and the longitudinal chromatic aberration from
wavefront-sensing was obtained both in the visible
(480 to 700 nm) and near infrared (IR) ranges
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CHROMATIC ABERRATION WITH BILATERAL HYDROPHOBIC AND HYDROPHILIC IOLS
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(700 to 900 nm). Chromatic difference of focus curves
were obtained from best focus data at each wavelength in each experiment, and the longitudinal
chromatic aberration was obtained from the slope
of linear regressions to those curves. The measured
longitudinal chromatic aberration was compared
between eyes of the same patient, with longitudinal
chromatic aberration values obtained on young
phakic patients performed with the use of the same
experimental system and with longitudinal chromatic
aberration reported on pseudophakic patients in the
literature.
monofocal and aspheric, but they differ in their material.
Table 2 shows the characteristics of the 2 IOL types.
Patients received a complete ophthalmic evaluation
prior to enrollment in the study and surgery at the Instituto
de Oftamología Avanzada, Madrid, Spain. The preoperative examination included uncorrected (UDVA) and
corrected distance visual acuity (CDVA), using the Early
Treatment of Diabetic Retinopathy Study (ETDRS) test,
biomicroscopy, corneal topography (Nidek Co., Ltd),
tonometry (Goldmann), and a fundus examination. Axial
length, anterior chamber depth, and white-to-white were
measured by means of optical biometry (IOLMaster, Carl
Zeiss Meditec AG). The IOL power was calculated with
the Holladay-2 formula, targeting emmetropia. The inclusion criterion for the study were good general health, no
ocular pathology, no complications during surgery, IOL
power between 18.00 D and 23.00 D, natural astigmatism
less than 1.50 D, bilateral implantation, clear capsule, and
postoperative CDVA better than 0.7. Surgeries in each eye
were conducted with a time difference of less than 7 days,
and the IOLs (hydrophobic or hydrophilic) were randomly
assigned to the first or second eye.
Postoperative clinical evaluations were conducted at 1
day, 1 week, and 1 month after surgery and included
UDVA and CDVA, using the ETDRS test, intraocular pressure (Goldmann), and biomicroscopy. At the 1-month
follow-up visit, the visual quality was assessed in the clinic
by the objective scatter index (OSI), modulation transfer
function (MTF), and Strehl ratio, measured using the Optical
Quality Analyzer System (OQAS, Visiometrics S.L.). Night
haloes were measured using the Halo software (version
1.0, University of Granada). Surgical procedures were
performed by 1 of 2 surgeons on an outpatient basis under
topical anesthesia. For phacoemulsification, the surgeon
made a 2.2 mm clear corneal incision. The IOLs were
PATIENTS AND METHODS
The longitudinal chromatic aberration was obtained from
psychophysical and wavefront-sensing measurements of
best focus at 8 different wavelengths on 18 eyes from 9
patients bilaterally implanted with the same design but
different material IOLs (hydrophobic, the Podeye and
hydrophilic, the Poday, PhysIOL) in each eye. Measurements were performed using a custom-developed polychromatic adaptive optics system.
Patients and Intraocular Lenses
Nine patients (mean age 73.92 years G 4.28 standard deviation [SD]) participated in the study. Table 1 shows the
age, refractive, and clinical profiles of the participants.
All patients were bilaterally implanted, 1 eye with the
hydrophobic double-C loop hydrophobic IOL, and the
contralateral eye with the hydrophilic IOL. Both IOLs are
Table 1. Optometric subjective refractions (spherical error, cylinder, axis) of the patients of the study, preoperatively and 1 month
postoperatively.
Preoperative Data
Subject
Sex
Lens Implanted
IOL Power
S1_R_EYE
S1_L_AY
S2_R_AY
S2_L_EYE
S3_R_EYE
S3_L_AY
S4_R_AY
S4_L_EYE
S5_R_AY
S5_L_EYE
S6_R_EYE
S6_L_AY
S7_R_EYE
S7_L_AY
S8_R_EYE
S8_L_AY
S9_R_AY
S9_L_EYE
M
Podeye
Poday
Poday
Podeye
Podeye
Poday
Poday
Podeye
Poday
Podeye
Podeye
Poday
Podeye
Poday
Podeye
Poday
Poday
Podeye
21.50
22.50
20.50
21.00
21.00
19.50
18.50
18.00
21.00
20.50
23.00
22.50
20.00
21.50
18.00
19.50
19.00
18.00
F
F
M
F
M
F
F
F
Sph
3
4
0.75
1.75
1.75
1.25
1.25
0.75
1.75
1.25
2.75
3.25
1
0.5
2.75
0
1
1
Follow-up (1 Month)
Cyl
Axis
CDVA (LogMAR)
1
0.5
1
1.25
1
1
1.25
0.5
1
0.5
0.75
1
2.25
0.5
1.5
1
0.5
0.75
80
90
90
95
55
115
180
12
90
65
120
110
20
180
105
70
70
100
0.4
0.3
0.15
0.2
0.3
0.2
0.1
0.2
0.2
0.25
0.3
0.25
0.5
0.3
0.2
0.1
0.2
0.25
Sph
1.5
0
0
0
0
0
1
0
0
0
0
0
1
0
0.5
0.5
0
0.75
Cyl
Axis
DCVA (LogMAR)
1.25
0
0
0
0.75
0.75
0
0
0
0
0
0
1
0
1.5
1
0.75
0.5
80
0
0
0
80
100
0
0
0
0
0
0
180
0
95
75
100
70
0
0
0
0.05
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Cyl Z cylinder; S_AY Z eyes implanted with PhysIOL Poday (hydrophilic); S_EYE Z eyes implanted with PhysIOL Podeye (hydrophobic); Sph Z spherical error.
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CHROMATIC ABERRATION WITH BILATERAL HYDROPHOBIC AND HYDROPHILIC IOLS
Table 2. Specifications of the Podeye and Poday IOLs provided by the manufacturer.
Model
35
Podeye
Poday
Material
Design*
Hydrophobic acrylic
GF material
Hydrophilic acrylic GF
material
Monofocal, 1-piece,
double C-loop
Monofocal, 1-piece,
double C-loop
Asph. AberrationCorrecting
Hazardous Light
Protection*
Packaging
State*
RI
Abbe
0.11 mSA
UV/blue
Hydrated
1.52
w41.91
0.11 mSA
UV/blue
Hydrated
1.46
w58.00
GF Z glistening free; RI Z refractive index; UV Z ultraviolet.
*Data from the intraocular lens specification.
implanted in the capsular bag with a single-use injection system (Microset, PhysIOL).
All participants were acquainted with the nature and
possible consequences of the study and provided written
informed consent. All protocols met the tenets of the Declaration of Helsinki and had been previously approved by
the Spanish National Research Council (Consejo Superior
de Investigaciones Científicas) Bioethical Committee. All
experiments were conducted under mydriasis (tropicamide
1.0%, 2 drops 30 minutes prior to the beginning of the study
and 1 drop every 1 hour).
Polychromatic Adaptive Optics Set-up
Measurements were conducted in a custom-developed
adaptive optics system at the Visual Optics and Biophotonics
Laboratory (Instituto de Optica,
Consejo Superior de Investigaciones Científicas) described in detail in a previous publication,20 which allowed control of the aberrations of the
subject while performing both psychophysical settings of
best focus and wavefront aberration measurements at
different wavelengths.
A super-continuum laser source (SC400 femtopower 1060,
Fianium Ltd.) was used as the light source of the system,
which allowed 2 independently filtered light fiber outputs
(visible-channel: 480 nm, 532 nm, 550 nm, 650 nm, and 700
nm and near IR channel: 780 nm, 827 nm, and 950 nm)
with a spectral bandwidth of approximately 5 nm (2 to 4
nm [visible]; 3 to 6 nm [near IR]). The laser power measured
at the corneal plane ranged between 0.5 mW and 50 mW,
within the American National Standards Institute safety
limits at all wavelengths.35–37
The main components of the adaptive optics system are
(1) A Hartmann-Shack wavefront sensor (microlens array
40 32, 3.6 mm effective diameter, centered at 1062 nm;
HASO 32 OEM, Imagine Eyes), which measures the ocular
aberrations; (2) A psychophysical channel (a slide with a
sunburst chart located in a conjugate pupil plane, monochromatically back-illuminated with light coming from the
super-continuum laser source and subtending 1.62 degrees
on the retina), which allows projection of psychophysical
stimuli. The luminance of the stimulus was 20 to 25 cd/m2
in the spectral range tested psychophysically (450 to 700
nm) and therefore in the photopic region at all wavelengths
(O10 cd/m2). (3) A Badal system that corrects for defocus.
(4) A pupil-monitoring channel. (5) An electromagnetic
deformable mirror (52 actuators, 15 mm effective diameter,
50 mm stroke; Mirao, Imagine Eyes), which for the purposes
of this study, was used only to correct the aberrations of the
optical system. Patients were aligned to the system (using an
x-y-z stage), using the line of sight as a reference. A 6 mm
artificial pupil was placed in a conjugate pupil plane to
ensure that the pupil diameter during the measurements
did not exceed that value. All optoelectronic elements of
the system (super-continuum laser source main source,
Badal system, retinal image camera, pupil camera,
Hartmann-Shack, and deformable mirror) are automatically
controlled and synchronized, using custom-built software
programmed in Visual CCC and C# (Microsoft Corp.). A
dual acousto-optic modulator system, controlled with the
software provided by the manufacturer, allowed automatic
selection of the measurement wavelength. The customdeveloped routines use the manufacturer's Software Development Kit for Hartmann-Shack centroiding detection and
wave aberration polynomial fitting. Wave aberrations
were fit by the 7th-order Zernike polynomials. The Optical
Society of America convention was used for ordering and
normalization of Zernike coefficients.38 The longitudinal
chromatic aberration of the system was measured, and measurements were corrected by the calibrated longitudinal
chromatic aberration of the optical system, as described in
detail in a previous publication.20
Experiments
The longitudinal chromatic aberration was obtained from
psychophysical and objective estimates of best focus for each
of the tested wavelengths. The best subjective focus was
initially searched with the stimulus back-illuminated at a
reference wavelength of 550 nm and set as zero. The
following experiments were performed, in this order:
Experiment 1: Psychophysical Best Focus at Different
Wavelengths Patients adjusted their best subjective
focus using the Badal system while viewing the stimulus back-illuminated with different wavelengths in
visible light (480 nm, 532 nm, 550 nm, 650 nm, and
700 nm). Patients were instructed to use the joystick
to move the Badal toward the position where the stimulus, initially blurred by means of defocus induced
with the Badal system, appeared sharp for the first
time. Patients performed a trial before the experiment
to become familiar with the test. The best focus settings
were repeated 3 times for each wavelength, presented
randomly.
Experiment 2: Hartmann-Shack Wave Aberrations at
Different Wavelengths Wave aberrations were obtained in visible light (480 nm, 532 nm, 550 nm, 650
nm, and 700 nm) and near IR light (780 nm, 827 nm,
and 950 nm), whereas the Badal system corrected the
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CHROMATIC ABERRATION WITH BILATERAL HYDROPHOBIC AND HYDROPHILIC IOLS
subjective defocus of the patient at 550 nm. The reference for best focus at 550 nm was obtained subjectively
under natural aberrations for experiments 1 and 2.
Data Analysis
The best subjective foci at each wavelength in experiment 1 were directly obtained from the automatic readings
of the Badal optometer. The best foci at each wavelength in
experiment 2 were obtained from the 2nd-order Zernike
defocus coefficients (C02 ) in microns, from the Zernike polynomial expansions fitting the wave aberrations measured
at each wavelength and using the expression D Z 16.
C02 .O3/p2, where C02 is the defocus Zernike coefficient in
microns, p is the pupil diameter, and D is the defocus in
diopters.
Chromatic difference of focus curves were obtained from
the best foci versus wavelength dataset of each experiment.
The longitudinal chromatic aberration was obtained from a
2nd-order polynomial fitting to those curves. The curves
are shifted in the vertical axis such that they cross zero at
550 nm (the reference wavelength) for a unique reference
for all techniques. For the psychophysical data, longitudinal
chromatic aberration was computed for the visible range
only. For the wavefront-sensing experiments, longitudinal
chromatic aberration was computed for visible (480 to
700 nm), near IR (700 to 950 nm), and total spectral ranges
(480 to 950 nm). For comparisons with the literature, the
chromatic difference of focus between 2 specific wavelengths
was also calculated.
Statistical analysis was performed with SPSS software
(International Business Machines Corp.) to test differences in the estimated longitudinal chromatic aberration
across experiments and conditions. A paired-samples
t test was performed to analyze specific differences
between conditions.
RESULTS
Wave Aberration Measurement at Different
Wavelengths
Wave aberrations were measured for both eyes and
all patients at 8 wavelengths. With wavelength, only
the defocus Zernike term shows significant differences, whereas astigmatism and higher-order aberrations (HOAs) do not show systematic changes.
Figure 1, A shows wave aberration maps (astigmatism
and HOAs) in patient 6 for the eye implanted with the
hydrophobic IOL (upper row) and hydrophilic IOL
(lower row) IOLs, illustrating little variation in the
wave aberrations with wavelength. On average across
eyes, the variation of root mean square (RMS) for astigmatism and HOAs was less than 4% across wavelengths. Figure 1, B shows the average RMS
(astigmatism and HOAs) across wavelengths for
each patient (eyes with hydrophobic and hydrophilic
IOLs, respectively). The RMS for astigmatism and
HOAs was, on average, 0.48 G 0.03 mm for the hydrophobic IOL and 0.39 G 0.03 mm for the hydrophilic
IOL (last bars in Figure 1, B).
Chromatic Difference of Focus From Psychophysical
and Wavefront-Sensing
Figure 2 shows the measured chromatic difference
of focus from psychophysical measurements (experiment 1: Figure 2, A for hydrophobic IOLs and (B) for
hydrophilic IOLs) and from the defocus Zernike coefficients from wavefront-sensing (experiment 2:
Figure 2 (C) for hydrophobic IOLs and (D) for hydrophilic IOLs) for all measured wavelengths in each
experiment. Lines represent polynomial fitting curves
to the data.
Longitudinal Chromatic Aberration: Differences
Across Eyes and Techniques
Figure 3 shows longitudinal chromatic aberration
from psychophysical measurements (A) in the visible
range (480 to 700 nm), from wavefront-sensing (B) in
the visible range (480 to 700 nm), and (C) in the total
spectral range (480 to 950 nm) for all patients and all
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Figure 1. (A) Wave aberration maps for the astigmatism and HOAs in patient 6 for the eye implanted with the hydrophobic (upper row) and
hydrophilic (lower row) IOLs, for all measured wavelengths. (B) Averaged RMS (astigmatism and HOAs) for all patients (eyes implanted
with hydrophobic and hydrophilic IOLs, respectively), and average across each IOL type. Data are for 6.0 mm pupils.
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Figure 2. Chromatic difference of focus from psychophysical best focus of monochromatic stimuli (A and B) and from defocus Zernike terms
from wavefront-sensing (C and D) for eyes implanted with the hydrophobic (A and C) and hydrophilic (B and D) IOLs, for all patients and
all measured wavelengths (psychophysical: 480 nm, 532 nm, 550 nm, 650 nm, and 700 nm; wavefront-sensing: 480 nm, 532 nm, 550 nm, 650
nm, 700 nm, 780 nm, 827 nm, and 950 nm). Data are referred to the best focus at 550 nm, set as zero defocus.
implanted eyes, hydrophobic (solid bars) and hydrophilic (dashed bars).
Table 3 shows the average longitudinal chromatic
aberration from psychophysical and wavefront-
sensing measurements in the different spectral ranges
measured for both IOL types. The longitudinal chromatic aberration from the hydrophobic IOL is
statistically higher than the longitudinal chromatic
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Figure 3. Longitudinal chromatic aberration from (A) subjective best focus and (B) wavefront-sensing for the visible (480 to 700 nm) and
(C) visible C near IR (480 to 950 nm) spectral range for all patients and averaged across patients. Solid bars indicate eyes implanted
with the hydrophobic IOL; dashed bars indicate eyes implanted with the hydrophilic IOL. Error bars in the subjective longitudinal chromatic aberration stand for standard deviation of repeated measurements.
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CHROMATIC ABERRATION WITH BILATERAL HYDROPHOBIC AND HYDROPHILIC IOLS
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Table 3. Averaged LCA from psychophysical and wavefront-sensing measurements in the different spectral ranges measured for both IOL
types and P values from paired-samples t test.
Psychophysical
Visible
NIR
Visible C NIR
480–700 nm
700–950 nm
480–950 nm
Wavefront-Sensing
Podeye
Poday
P Value
Podeye
Poday
P Value
1.37 G 0.08 D
1.21 G 0.08 D
.003*
0.88 G 0.07 D
0.39 G 0.07 D
1.27 G 0.09 D
0.73 G 0.09 D
0.29 G 0.08 D
1.02 G 0.13 D
.004*
.184
.004*
aberration from the hydrophilic IOL in both techniques in the visible range as well as in the total spectral range. Intersubject variability is small for both
techniques: G0.008 D for the psychophysical technique (visible range) and G0.006 D for wavefrontsensing (total spectral range).
DISCUSSION
We measured the longitudinal chromatic aberration
in a wide range of wavelengths by using a psychophysical method and wavefront-sensing at multiple
wavelengthsdboth implemented in the same polychromatic adaptive optics systemdon pseudophakic
eyes bilaterally implanted, 1 eye with the hydrophobic Podeye IOL and the contralateral eye with Poday
the hydrophilic IOL. The study design minimizes
potential patient bias, particularly in psychophysical
measurements (same patient perform the subjective
best focus settings with either IOL) as well as a direct
comparison of both lower-order aberrations and
HOAs across groups.
We found that the eyes implanted with the hydrophobic IOL exhibit a small but consistently higher longitudinal chromatic aberration than the eyes implanted
with the hydrophilic IOL (a difference of 0.16 D and
0.15 D from psychophysical and wavefront-sensing
methods, respectively, in the visible 480 to 700 nm
range). The difference is consistent with the lower
Abbe number of the hydrophobic material. The IOL
material potentially has relevance on visual performance, as the IOL material affects the chromatic aberration of the eye.
We found that the longitudinal chromatic aberration from the psychophysical method is consistently
higher (P Z .001) for all eyes than the longitudinal
chromatic aberration obtained from wavefrontsensing, by 0.48 D (35.41%) for the hydrophobic IOL
and 0.48 D (39.43%) in the hydrophilic IOL. Similar differences were also found in a previous study20 on
young phakic eyes, using the same experimental system (0.61 D, 40.4%). Lower values of longitudinal
chromatic aberration from reflectometric than from
psychophysical had been also reported earlier. Some
studies1,7,39 had attributed those differences to the
presence of HOAs, although our previous study20 discarded this hypothesis by performing measurements
under correction of natural aberrations with adaptive
optics, which showed similar discrepancies between
psychophysical and reflectometric (wavefront-sensing
and double-pass–based) techniques. It is likely that the
differences arise by wavelength-dependent reflectivity
of the different retinal layers. In our previous study,20
we showed that deviations in the best focus from psychophysical and reflectometric techniques occurred
both at the short and long range of the spectrum,
with higher shift in red than in blue light. We hypothesized that blue light was reflected anteriorly from
the photoreceptors’ inner segments, approximately
in the retinal nerve fiber layer, and that red light was
reflected behind the photoreceptors, in the choroid.
This fact is interesting because in red light, the contribution of the choroidal reflections is large compared
with that of reflections originating in the inner
layers of the retina40 and might explain the higher shift
in red than in blue light. In any case, the relative difference in longitudinal chromatic aberration in eyes
implanted with different IOLs remains constant
regardless of the measurement technique.
The longitudinal chromatic aberration measured in
the pseudophakic eyes of the current study can be
compared with the longitudinal chromatic aberration
measured in our previous study on young phakics, using the same methods,20 and for similar wavelength
ranges (Figure 4). For both techniques, we found that
the longitudinal chromatic aberration in phakic eyes
is higher than in the pseudophakic eyes. These differences were statistically significant with both techniques for the hydrophilic IOL, but only for the
wavefront-sensing technique for the hydrophobic
IOL (independent-samples t test): psychophysical:
hydrophilic phakic, P Z .002; wavefront-sensing: (1)
visible, hydrophobic phakic, P Z .041, hydrophilic
phakic, P Z .009; (2) near IR, hydrophilic phakic,
P Z .008; (3) visible C near IR, hydrophobic phakic,
P Z .018, hydrophilic phakic, P Z .02. The longitudinal chromatic aberration in these pseudophakic eyes
is, on average, similar than the longitudinal chromatic
aberration in normal phakic eyes, whether measured
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Figure 4. Longitudinal chromatic
aberration averaged across patients for the hydrophobic IOL
(red solid bars), hydrophilic
IOL (red dashed bars), and phakic
eyes (green solid bars) for spectral
ranges in the visible, near IR,
and total spectral ranges, from
subjective best focus and wavefrontsensing. *, **Statistically significant
(P ! .05) and highly statistically
significant (P ! .01) differences,
respectively, between pseudophakic and phakic eyes. Error
bars stand for measurement error
for subjective longitudinal chromatic aberration and intersubject
variability in wavefront-sensing.
with the psychophysical or reflectometry technique, in
the same spectral ranges.
Chromatic aberrations play a major role on the
quality of vision1,29,41,42; however, only a few studies
have addressed the chromatic properties of the IOLs
and the chromatic aberration of the pseudophakic
eyes in vivo. Our study provides estimates of the
longitudinal chromatic aberration measured in a
wider spectral range in the visible and near IR than
that of previous studies, using psychophysical and
wavefront-sensing measurements. Figure 5 shows
the chromatic difference of focus found in the current study (psychophysical data in blue; wavefrontsensing, in pink), in comparison with in vivo chromatic
difference of focus (in the corresponding spectral
range) from previous studies from psychophysical
(red triangles) and reflectometric (green circles) techniques with different types of IOLs.27,33,34 In general,
our results fall within values reported by previous
studies that used both psychophysical and reflectometric techniques, with the data from psychophysical
techniques showing consistently higher longitudinal
chromatic aberrations than those from reflectometry
techniques.
WHAT WAS KNOWN
Chromatic aberrations play a major role on the quality of
vision, and the longitudinal chromatic aberration has
been extensively measured in phakic eyes. Most estimates of longitudinal chromatic aberration in pseudophakic eyes come from computations based on the IOL
material Abbe number, and very few come from actual
measurements on patients.
WHAT THIS PAPER ADDS
There were significant but small differences in the longitudinal chromatic aberration with hydrophobic and hydrophilic IOLs, the longitudinal chromatic aberration being
consistently smaller with hydrophilic IOLs. The longitudinal chromatic aberration from psychophysical measurements was consistently higher than those from
wavefront-sensing, also in pseudophakic eyes.
Figure 5. Chromatic difference of
focus from the psychophysical
(blue triangles) and wavefrontsensing (pink circles) measurements
of the current study and other psychophysical (red triangles) and
reflectometry (green circles) data in
the literature. The measured chromatic range differed across studies,
and it is indicated by the symbols
in the end of the regression lines.
Data are referred to zero defocus
at 550 nm.
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1102
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1104
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1120