Download Wavefront Ablation Profiles in Refractive Surgery

REVIEW
Wavefront Ablation Profiles in Refractive
Surgery: Description, Results, and
Limitations
David Smadja, MD; Glauco Reggiani-Mello, MD; Marcony R. Santhiago, MD;
Ronald R. Krueger, MD, MSE
ABSTRACT
PURPOSE: To provide an overview of the clinical results
of different ablation profiles based on wavefront technology and discuss their characteristics and limitations.
METHODS: Literature review of studies reporting results
of ablation profiles based on wavefront technology in
virgin healthy eyes.
RESULTS: Over the past 10 years, a large number of
studies comparing different treatment algorithms and
newer excimer laser platforms have been published.
Thirty-six clinical studies including 3637 eyes analyzing the clinical results obtained after wavefront-guided,
wavefront-optimized, and Q-factor profiles have been
reviewed. Although wavefront-driven profiles allowed reduction of the amount of induced optical aberrations
with conventional ablations, thereby improving the quality of vision, it appears that no algorithm of treatment or
excimer laser platform has demonstrated a clear superiority over another. Wound healing and unexpected biomechanical response to surgery affect the accuracy of
customized treatments and produce variable results. In
addition, it is difficult to rigorously analyze and compare
findings among different studies because of the diverse
variety in which the data are reported.
CONCLUSIONS: Despite several technological improvements over the years, wavefront ablation profiles have
not consistently demonstrated superiority in terms of visual acuity and lower order aberrations compared to the
standard procedure, although the induction of higher
order aberrations has been reduced. The concept of an
individualized eye model has emerged recently, based
on the optical ray tracing algorithm, and could theoretically provide a higher level of customization, thus
fulfilling the promise of “super vision.” [J Refract Surg.
2012;28(3):xxx-xxx.]
doi:10.3928/1081597X
D
uring the past decade, the field of refractive surgery
has been flooded with dramatic advances introduced
by new technologies. Aside from new applications
of the femtosecond laser, further improvements were achieved
with the development of new excimer laser platforms with
higher repetition rates, faster eye trackers, and customized
ablation profiles. Along with this rapid development, the primary goal of refractive surgery has evolved and today aims to
provide “super vision” in terms of visual performance.
The quest for “super vision” has generated a surge of interest, leading to the development of new algorithms of treatment and numerous technological improvements in the newer generations of excimer lasers. A large number of studies
comparing different ablation profiles and different excimer
laser platforms have been published. However, has an ideal
algorithm of treatment emerged from these studies? Does one
ablation profile clearly demonstrate superiority compared to
the other in regards to visual acuity, contrast sensitivity, or
night symptoms?
After describing the technical properties of the various treatment algorithms using wavefront technology, we attempted to
provide an overview of the clinical results available among
several comparative studies. The factors tending to limit the
success of these new procedures were also discussed along
with future perspectives in the field. Studies reporting results
of such profiles for retreatments, highly aberrated eyes, keratoconus, or transplant as well as results of topography-guided
treatments were not included in this review.
TECHNICAL CONSIDERATIONS OF ABLATION PROFILES
The technical aspects of excimer laser ablation have evolved
considerably since the introduction of the formula for standard
From the Refractive Surgery Department, Cole Eye Institute, Cleveland Clinic
Foundation, Cleveland, Ohio.
Dr Krueger receives consulting and research funds from Alcon Laboratories
Inc, Ft Worth, Texas. The remaining authors have no financial interest in the
materials presented herein.
Correspondence: David Smadja, MD, 1701 E 12th, W22Q, Cleveland, OH
44114. Tel: 216.501.3340; E-mail: [email protected]
Received: April 9, 2011; Accepted: December 6, 2011
Journal of Refractive Surgery • Vol. xx, No. x, 2012
1
Wavefront Ablation Profiles/Smadja et al
sphere-cylindrical correction described by Munnerlyn
in 1988.1 Over the years, and with the surge of interest generated by wavefront technology, advanced laser
treatment algorithms based on different concepts have
been developed, aiming to correct not only lower but
also higher order wavefront aberration errors.
WAVEFRONT-GUIDED TREATMENT REQUIREMENTS
Towards the end of the past decade, a new era began
with the introduction of ablation profiles guided by the
wavefront map to sculpt the cornea in a way to correct
preexisting aberrations and reduce surgically induced
aberrations. To achieve the precision required for this
profile, advancements in excimer laser technology
were needed.
The broad beam cannot treat small irregularities in
the cornea and most current devices use flying-spot
technology, in which smaller beams (0.5 to 1.0 mm)
are used for better and more accurate results in custom
ablations and the correction of irregular astigmatism.
Spot sizes ⬍1 mm are required to adequately correct
up to the fourth order terms whereas 0.6-mm beams
are needed to treat up to the sixth order terms.2 Some
devices have a variable spot size (eg, VISX S4; Abbott
Medical Optics Inc, Santa Ana, California).
The shape of the beam is also important to produce
a smoother surface, which is best achieved with an
optimized spot overlap.3 The energy is delivered in a
Gaussian profile (greater energy density in the center of
the beam than the periphery) with the Allegretto Wave
Eye-Q laser (Alcon Laboratories Inc, Ft Worth, Texas),
MEL 80 (Carl Zeiss Meditec AG, Jena, Germany), and
NIDEK NAVEX (NIDEK Co Ltd, Gamagori, Japan).4
The flying-spot laser must be delivered precisely for
an accurate wavefront correction and requires highspeed eye-tracking systems because of the smaller spot
size and risk of individual pulse decentration and misplacement compared to broad-beam lasers. Centration
needs to be accurate,5 as minimal misalignment or cyclotorsion that would normally cause only a small undercorrection in the spherical-cylindrical profile can
induce a completely different aberration pattern. Theoretical modeling indicates that a decentration ⬎0.10
mm can induce rather than reduce aberrations during
myopic wavefront-guided treatments.6
The repetition rate of laser pulses is another feature
that varies among excimer lasers. Repetition rate correlates directly with treatment time. Longer periods
cause drying of the corneal stroma and loss of fixation,
which are unacceptable with customized profiles. In
the first broad-beam lasers, the repetition rate was low
(6 to 10 Hz). With scanning-spot technology, the rate
needed to increase; otherwise, treatment times would
2
be longer because more pulses would be needed for the
same ablation.
The scanning-spot frequency must not exceed a rate
that can be followed by the tracking system.6 In addition, excessive thermal damage in adjacent tissue can
occur with repetition rates higher than 60 Hz. Modern
devices, such as the Amaris excimer laser (SCHWIND
eye-tech-solutions GmbH & Co KG, Kleinostheim, Germany), use higher repetition rates up to 500 Hz for faster treatments with scanning spots. In these devices, a
repetition rate in a determined locale does not exceed
40 Hz because the pulses are being applied sequentially
in different locations of the cornea to prevent thermal
damage.7
WAVEFRONT-OPTIMIZED PROFILE
Controversy remains concerning the proper definition of the optimal ablation profile. Artal et al8 found
that eyes with smaller wavefront aberrations did not
achieve the best visual quality. In 2004, Mrochen et
al9 designed an optimized aspheric profile to compensate only for the spherical aberration induced with
the conventional treatment, preserving the preexisting
optical aberration pattern of the eye. Since then, this
algorithm of treatment has been introduced in several modern excimer laser platforms and is in theory
less dependent on technical aspects that are critical in
wavefront-guided treatment. This profile has been developed considering the loss in ablation efficacy due
to the angle of incidence of the excimer laser pulses
in the midperiphery (ie, the cosine effect, leading to
an oval beam of reduced energy on the peripherally
sloping cornea), which can lead to a decrease in the
intended ablation depth in this region and an increase
in spherical aberration. The optimized profiles compensate for this effect by increasing the pulse energy
in the periphery.
CUSTOM-Q FACTOR PROFILE
Based on the concept that an ideal asphericity of the
cornea could lead to a better visual performance, the
“Q-factor adjusted” profile was developed to manipulate the asphericity by selecting the desired target of
Q-value. Based on an aspheric eye model, Manns et
al10 suggested that a minimum of spherical aberration
would be obtained at a target Q-factor of approximately
⫺0.4. Some excimer laser platforms are equipped with
this profile such as the Allegretto Wave Eye-Q laser
with the adjustable “Q software mode,” allowing the
surgeon to target the Q-value independently from the
preexisting spherical aberration and the NAVEX system with the “Optimized Prolate Ablation (OPA).” The
OPA profile uses both corneal topography and ocular
Copyright © SLACK Incorporated
Wavefront Ablation Profiles/Smadja et al
aberrometry to either maintain the natural corneal
shape of the cornea after surgery or to target a specific
corneal asphericity to improve the visual quality.11 The
MEL 80 platform is equipped with the CRS-MASTER Laser Blended Vision module, which allows manipulation of the corneal asphericity to increase the depth of
focus to overcome presbyopia. This module has been
used to create a non-linear aspheric ablation to provide
micro-monovision.12
CONVENTIONAL TREATMENT AND DEVELOPMENT OF
CUSTOMIZED ABLATION PROFILES
The main complaints reported by patients after conventional excimer laser refractive surgery are blurred
vision under low light conditions, halos, and glare,
which lead to decreased visual quality.13 These complaints could occur despite achieving 20/20 visual
acuity on the Snellen chart and are believed to be due
to the surgically induced increase in high order aberrations (HOAs) after laser treatment.14 By reshaping the
cornea, the lasers modify the curvature and asphericity in a way that induces an increase in HOAs, especially spherical aberration, due to the optical effect of
the transition zone between the treated and untreated
cornea. The amount of induced optical aberrations is
correlated with the level of attempted refractive correction.15 It is well known that the effects of significant
HOAs degrade the quality of the optical image on the
fovea. Although some controversy exists, it has been
suggested that the correction of HOAs could lead to
an improvement in contrast sensitivity and visual acuity.16,17 Therefore, the introduction of a customized
correction based on the wavefront pattern of the eye
was promising to overcome the main issues found in
the conventional treatment.
OVERVIEW OF THE CLINICAL RESULTS
Over the past 10 years, a large number of studies
comparing the different treatment algorithms and
newer excimer laser platforms have been published.
Despite efforts to show the superiority of wavefrontguided correction over the standard treatment, or a
customized profile over another, it remains unclear
whether an ablation profile has demonstrated its superiority over another in terms of visual performance and
patient satisfaction.
For clarity, and despite the lack of standardization
concerning patient selection and treatment parameters
surrounding the majority of these studies, we attempted to summarize the main results reported in the literature using the different available wavefront ablation
profiles (wavefront-guided, wavefront-optimized, and
custom-Q) in virgin healthy eyes.
Journal of Refractive Surgery • Vol. xx, No. x, 2012
Potential advantages of using these ablation profiles
in highly aberrated eyes such as retreatment for decentered ablation, small optical zone, irregular astigmatism, keratoconus, or transplant are not discussed in
this review.
INTRODUCTION OF WAVEFRONT ABLATION PROFILES
Wavefront-guided Treatment. To avoid induction
and reduce preexisting aberrations of the eye, the
wavefront-guided profile was developed. The first results reported by Seiler et al18 in 2000 after performing
wavefront-guided LASIK on 35 eyes were encouraging. After 3 months, 93.5% of eyes had uncorrected
distance visual acuity (UDVA) of 20/20 or better, and
supernormal vision, defined as 20/10 or better, was
achieved in 16%. Postoperative HOAs decreased in
22.5% of eyes. However, optical aberrations increased
on average by a factor 1.44 with a 5-mm pupil. More recently, studies using different wavefront-guided platforms have supported these primary results, reporting
improvements in visual acuity and contrast sensitivity
postoperatively.19-21
Although this ablation profile was developed with
the goal of avoiding both induction of optical aberrations and reduction of preexisting aberrations, recent
studies reported the limitations of such customized
treatments. Bottos et al22 retrospectively analyzed 177
myopic eyes and 32 hyperopic eyes that underwent
wavefront-guided LASIK for correction ranging from
⫺9.87 to ⫹6.25 diopters (D). They reported a high correlation between the amount of preoperative refractive
error and asphericity changes (r2=0.81, P⬍.001) and induced corneal spherical aberrations (r2=0.34, P⬍.001)
and thus concluded that changes depended on the
magnitude of the refractive correction. Additionally,
they highlighted the tendency for the postoperative
Q-value and spherical aberration to be more positive
after myopic ablation and more negative after hyperopic ablation. Keir et al23 reported similar results in a
prospective study analyzing the impact of hyperopic
wavefront-guided LASIK on HOAs and contrast sensitivity. A significant change was noted in postoperative
spherical aberration, which had a reverse sign (became
negative) and a high correlation was found between
low contrast visual acuity and induced spherical aberration (r2=0.62, P⬍.001).
With the surge of interest generated by the wavefront-guided treatment, the need to improve outcomes
to meet expectations led the current generation of lasers to undergo many technological improvements
over the past 10 years. Following the company-driven
technological developments, several studies comparing different wavefront-guided laser platforms have
3
Wavefront Ablation Profiles/Smadja et al
been published despite the bias introduced such as the
familiarization to the use of a new platform and the
need for nomogram adjustment that is surgeon-dependent. Despite the introduction of different technological advancements in all platforms, superiority of one
system over another has yet to be established in the
peer-reviewed literature.24-26
Wavefront-optimized Treatment. Good visual outcomes have also been reported with the wavefrontoptimized profile. George et al,27 using the Allegretto
Wave Eye-Q laser, found that 92% of myopes and 63%
of hyperopes achieved UDVA of 20/20 after 3 months,
and no statistically significant surgically induced
spherical aberration was noted among myopic eyes.
Using the AMARIS platform, Arbelaez et al28 found
similar results, with 84% of 50 myopic eyes achieving
UDVA of 20/20 or better and 40% achieving UDVA of
20/16 or better after 6 months. No significant changes in aberration metrics were found postoperatively.
Vongthongsri et al29 also reported good results after
myopic treatment using the optimized aspheric treatment zone (OATz) profile, which is available with the
NIDEK NAVEX system. In their study, 94.2% of eyes
were within 0.50 D of the intended refraction and 75%
of eyes achieved UDVA of 20/20 or better after a mean
follow-up of 3 months.
RESULTS OF COMPARATIVE STUDIES BETWEEN
CONVENTIONAL AND WAVEFRONT PROFILES
Conventional vs Wavefront-guided Treatment. Numerous studies published in the literature have failed
to demonstrate a clear advantage of wavefront-guided
over conventional treatment for low to moderate myopia and myopic astigmatism.30,31 In a contralateral
study comparing 10 eyes treated with conventional
LASIK and 10 eyes with wavefront-guided LASIK,
Phusitphoykai et al30 did not find any statistically
significant differences regarding visual outcomes and
optical aberrations postoperatively. More recently,
Dougherty and Bains,31 in a series of 290 eyes, compared the results of conventional LASIK using the NIDEK EC-5000 (NIDEK Co Ltd, Gamagori, Japan) with
those obtained after using 2 different wavefront-guided
laser platforms, the VISX S4 CustomVue (VISX, Santa
Clara, California) and CustomCornea (Alcon Laboratories Inc). No statistically significant differences were
observed regarding safety, efficacy, or predictability
among groups.
Other studies concluded that wavefront-guided ablation induces fewer aberrations than conventional
treatment, but still increases total HOAs.32,33 Kim et
al,32 in a contralateral eye comparative study including
24 patients treated with LASIK using the Technolas
4
217z excimer laser (Bausch & Lomb Surgical, Rochester, New York), reported a reduction in induced HOAs
following wavefront-guided treatment. However, no
clinical differences in terms of visual acuity, patient
preference, and mesopic contrast sensitivity were observed between the two treatments.
Another group of studies reported a significant superiority of wavefront-guided compared to conventional treatment in terms of night visual performance
and glare symptoms.20,34 Schallhorn et al20 observed a
significant improvement of night driving visual performance after wavefront-guided correction compared to
conventional treatment.
Conventional Treatment vs Optimized Profile. Although several authors reported good visual outcomes
and only a small increment in surgically induced HOAs
after treatment with aspheric profiles,27,28 few comparative studies with conventional treatment are available
in the peer-reviewed literature. Mastropasqua et al35
compared the visual outcomes and wavefront errors of
50 myopic eyes treated with photorefractive keratectomy (PRK) using an aspheric profile with the MEL 80 laser platform to 24 myopic eyes treated with a standard
treatment using the MEL 70 laser platform. They found
that both treatments caused an increase in HOAs. Nevertheless, the total wavefront error and spherical aberration were significantly lower with the aspheric profile compared to conventional treatment. de Ortueta
et al36 compared 70 myopic eyes with conventional
treatment with 70 eyes treated with an aspheric profile
using the ESIRIS laser platform (SCHWIND eye-techsolutions GmbH & Co KG). Their results were similar
to those reported by Mastropasqua et al,35 with an increase of HOAs and spherical aberrations after ablation
in both groups, but a smaller induction of HOAs after
aspheric ablation than standard ablation.
When analyzing these data, despite showing a small
reduction in the induction of HOAs with the wavefront-optimized profile, it is not possible to conclude
that it leads to superior visual performance compared
to the standard treatment.
RESULTS OF COMPARATIVE STUDIES BETWEEN DIFFERENT
WAVEFRONT ABLATION PROFILES
Wavefront-guided vs Wavefront-optimized. Both
of these profiles have suggested a smaller increase in
HOAs postoperatively compared to the conventional
treatment. The wavefront-optimized profile was introduced to preserve the natural prolate shape of the
cornea and to compensate for the so-called “cosine effect.” The idea is also to reduce the variables that can
influence the final outcome, resulting in a more simple
procedure. In wavefront-guided treatments, as an exCopyright © SLACK Incorporated
Wavefront Ablation Profiles/Smadja et al
ample, the quality of the wavefront map and correct
axis alignment tend to be more crucial than in wavefront-optimized treatments.
To determine the place of this new algorithm in the
strategy of treatment, Stonecipher and Kezirian,37 in
a United States Food and Drug Administration trial,
compared 374 myopic eyes randomized to receive
either the wavefront-optimized profile or wavefrontguided profile (which was approved for use in the
United States in 2003) using the Allegretto Wave EyeQ. Regarding the visual outcomes after 3 months, most
of the results analyzed did not show any statistically
significant differences between groups, except for the
percentage of eyes that achieved uncorrected distance
visual acuity of 20/16, which was slightly higher in
the wavefront-optimized group (76% vs 64%). Regarding postoperative wavefront errors, no difference was
found between groups in 83% of eyes that had ⬍0.30
μm of preoperative HOA root-mean-square (RMS). In
eyes that had ⬎0.30 μm of preoperative HOA RMS,
the wavefront-guided profile resulted in less HOAs
postoperatively than the wavefront-optimized profile.
In terms of these results, the authors concluded that
wavefront-guided treatment did not have an advantage
over wavefront-optimized treatment in the majority
of cases. They suggested wavefront-guided treatment
be considered if the magnitude of preoperative HOA
RMS is ⬎0.35 μm, which represents approximately
20% to 25% of eyes in the overall general population. Other recent studies have supported these findings.38,39 Hantera39 reported similar results with the
NAVEX, comparing the OATz algorithm (equivalent
to the wavefront-optimized profile) to the optimized
path difference custom aspheric treatment (equivalent
to the wavefront-guided profile). The author found
a greater tendency for increasing HOAs in eyes with
⬍0.30 μm HOA RMS preoperatively in the wavefrontguided group. The reverse tendency was observed in
the wavefront-optimized group. Therefore, the author
recommended using the wavefront-optimized profile
for eyes with preoperative HOA RMS ⬍0.30 μm. Recently, Feng et al40 supported these findings in a metaanalysis including 7 studies and 930 eyes comparing
wavefront-guided to wavefront-optimized LASIK for
myopia. They reported no difference between profiles
in terms of UDVA, corrected distance visual acuity
(CDVA), and induction of HOAs for patients with preoperative HOA RMS ⬍0.30 μm. However, in eyes with
preoperative HOA RMS ⬎0.30 μm, the wavefrontguided profile induced less postoperative HOAs than
the wavefront-optimized profile.
In a prospective, randomized, double-masked study
of 200 eyes that underwent LASIK for myopia and
Journal of Refractive Surgery • Vol. xx, No. x, 2012
astigmatism, Yu et al41 found no statistically significant difference between treatments after 6 months. The
variables analyzed included visual acuity, total HOAs,
and contrast sensitivity in dim light conditions. An
interesting finding in this study was the absence of a
significant difference in patient satisfaction level after
both treatments, evaluating night driving symptoms;
visual symptoms such glare, halos, or ghost images;
fluctuation of vision; and dryness. Perez-Straziota et
al,42 comparing 66 eyes receiving either wavefrontguided or wavefront-optimized LASIK, respectively, found similar results with no difference between
groups in terms of UDVA, CDVA, manifest refraction
spherical equivalent, and HOAs after 3 months. Another interesting finding in this study was that 14 eyes
initially scheduled for wavefront-guided treatment
had to be converted to wavefront-optimized for poor
limbal ring alignment (8 eyes), a Wavescan that was
inconsistent with the manifest refraction (5 eyes), and
no iris registration (1 eye), indicating the high level of
requirements for wavefront-guided compared to wavefront-optimized treatment.
George et al27 retrospectively evaluated the results
of 285 eyes treated with the wavefront-optimized profile using the WaveLight Allegretto laser and found
excellent visual outcomes with a low postoperative
increase in HOAs of ⫹0.03 μm for myopic LASIK and
0.00⫾0.07 μm spherical aberration induced after 3
months. Comparing these results to former outcomes
obtained with the wavefront-guided treatment using
the LADAR CustomCornea, they reported a greater increase in surgically induced spherical aberration with
the wavefront-guided compared to the wavefront-optimized profile after myopic LASIK.
These results, although in contrast with previous
studies comparing both ablation profiles, are consistent with the primary aim of the wavefront-optimized
profile, which is to preserve the natural shape of the
cornea without inducing ocular aberrations.
Custom-Q Profile. Koller et al43 compared this treatment algorithm to wavefront-guided ablation in a contralateral eye study of 35 patients treated with LASIK
for myopia and astigmatism. They reported equal safety and efficacy using both treatments. Although the
corneal asphericity was less impaired in the Q-factor
profile up to ⫺5.00 D, no statistically significant difference was noted regarding visual or optical parameters up to ⫺9.00 D, except after 1 month when the
wavefront-guided group had significantly lower comalike aberration. The unexpected result was the similar
induced spherical aberration in both groups. Ghoreishi
et al,44 in a contralateral eye study comprising 56 patients, found similar results comparing one eye treated
5
Wavefront Ablation Profiles/Smadja et al
with custom-Q PRK targeted to a Q-value of ⫺0.2 and
the fellow eye treated with wavefront-guided PRK.
They found no differences in terms of safety and visual
outcomes and a similar increase in spherical aberrations postoperatively. Stojanovic et al45 compared this
same algorithm of treatment with a target Q-value set
to ⫺0.5 or ⫺0.6, depending on the patient’s preoperative asphericity and age, to the wavefront-optimized
profile. All eyes showed a tendency towards an oblate
shift postoperatively; however, less shift was noted in
the Custom-Q group than in the wavefront-optimized
group. No differences were found regarding safety,
refractive outcomes, low contrast visual acuity, and
wavefront errors.
Of the few studies available in the peer-reviewed literature comparing the custom-Q profile to other ablation profiles, most failed to demonstrate any superiority of this algorithm of treatment over another. These
findings also suggest that the custom-Q profile was not
able to deliver exactly the attempted asphericity with
the current technology, probably affected also by an
unexpected wound-healing response.
In a multivariate regression analysis of 160 eyes
that underwent wavefront-guided treatment, Tuan and
Chernyak46 found no significant correlation between
the change in corneal shape and visual performance.
The authors concluded that no standard optimal
asphericity exists and the ideal shape needs to be customized on an individual basis.37
LIMITING FACTORS
PATIENT-RELATED LIMITATIONS
Despite all technological improvements, final outcome is limited by patient-specific factors, such as
wound healing and biomechanical response. Current
excimer lasers are precise and can sculpt a plastic
model with submicron precision. However, corneal
wound-healing response tends to smooth features applied to the corneal stroma and potentially avoid the
effect of the intended ablation to correct HOAs. As
mentioned by Netto and Wilson,47 hyperplasia of the
epithelium within the ablated zone by even a single
cell is likely to have a major affect on a customized corneal treatment, given that the diameter of an epithelial
cell is larger than the ablation volume to correct 1 μm
RMS of wavefront irregularity in a single point.
Furthermore, regarding the biomechanical response,
Dupps and Roberts48 suggested that a central ablation,
by releasing tension in the periphery, can lead to expansion and thickening in the midperiphery causing
a secondary flattening of the center and thus a change
in curvature. These postoperative issues are known
6
to hinder the accuracy of customized treatments and
produce variable results because the majority of these
profiles do not take into account these unexpected responses.
Wavefront-guided treatment aims to correct the
preexisting aberrations and avoid the induction of significant amounts of aberrations to improve visual performance, but questions have been raised with recent
publications showing that the total RMS of HOAs is
not a reliable predictor of visual performance. It has
been shown that visual acuity varied significantly depending on the combination of Zernike modes and
the relative contribution of each mode.49 From these
findings, it remains to be seen whether the treatment
of all HOAs is more beneficial for visual performance
and if not, which specific combinations of aberrations
must be treated or, on the contrary, maintained or unchanged. Technology, such as adaptive optics, might
be a useful tool to combine with wavefront technology to reach a higher level of customization. Preoperative patient simulations with different combinations
of aberrations might help in determining the specific
amount and Zernike mode of aberration to target with
the treatment.
TECHNOLOGY-RELATED LIMITATIONS
Wavefront sensors are precise and reproducible
when dealing with low to moderate magnitudes of
higher order aberrations. However, because the measurement of ocular aberrations is based on the position of a collection of spot images, if the eye is highly
aberrated (decentered ablations, small optical zone,
or irregular astigmatism), the spots overlap and the
computer cannot determine the origin of an individual spot, reducing the precision of the measurement.
In addition, data analysis by a wavefront sensor does
not take into account the quality of individual spots
formed by the lenslet array, which can cause false
readings in opacities and disruption of the tear film.
Furthermore, differences in the technology used by the
different wavefront sensing devices such as HartmannShack, Tscherning (position-based aberrometers), or
dynamic skiascopy (time-based aberrometers) lead to
different wavefront measurements, thereby further increasing the discrepancy in results.50
FACTORS LIMITING INTERPRETATION AND ANALYSIS OF THE
AVAILABLE RESULTS
Due to the disparity in results among the different
comparative studies, and although customized ablation seems to provide better outcomes than conventional ablation in terms of induced aberrations, it appears that no algorithm of treatment or excimer laser
Copyright © SLACK Incorporated
22
(2011)
Journal of Refractive Surgery • Vol. xx, No. x, 2012
(2006)
(2009)
(2008)
28
Padmanabhan et al
WFO vs Q
Stojanovic et al45 (2008)
46
112
70
23
54
134
200
374
70
74
48
290
36
285
50
200
62
209
Eyes (N)
NCL
CL
CL
NCL
CL
NCL
NCL
NCL
NCL
CL
CL
NCL
NCL
NCL
NCL
NCL
NCL
NCL
CL/NCL
Design
R
P
P
P
P
R
P
P
R
P
P
R
R
R
R
R
P
R
P/R
X
X
X
Keratome
Keratome
Keratome
Keratome
Keratome
FS laser
Keratome
Keratome
Keratome
Keratome
FS laser
FS laser
FS laser
FS laser
FS laser
LASIK
Technique
PRK
Allegretto
Allegretto
Allegretto
CXIII
Allegretto
Multiple
Allegretto
Allegretto
ESIRIS
MEL
Zyoptix
Multiple
Multiple
Allegretto
Amaris
Multiple
LADAR
VISX S4
Excimer
Platform
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
VA
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
WF
X
X
X
X
X
X
X
X
CS
Parameters analyzed
X
X
X
Symptom
CL/NCL = contralateral/noncontralateral study, P/R = prospective/retrospective study, VA = visual acuity, WF = wavefront aberration error, CS = contrast sensitivity, WFG = wavefront-guided,
WFO = wavefront-optimized, Cv = conventional, Q = adjusted Q profile, PRK = photorefractive keratectomy, FS = femtosecond
VISX S4 (Abbott Medical Optics Inc, Santa Ana, California); LADAR, Allegretto (Alcon Laboratories Inc, Ft Worth, Texas); Amaris (SCHWIND eye-tech-solutions, Kleinostheim, Germany); Zyoptix (Bausch &
Lomb, Rochester, New York); MEL (Carl Zeiss Meditec, Jena, Germany); ESIRIS, CXIII (NIDEK Co Ltd, Gamagori, Japan)
WFG vs Q
WFG vs Q
Ghoreishi et al44 (2009)
WFG vs WFO
WFG vs WFO
WFG vs WFO
WFG vs WFO
WFG vs WFO
WFO vs Cv
WFO vs Cv
WFG vs Cv
WFG vs Cv
Koller et al43 (2006)
Hantera39 (2009)
(2008)
42
Perez-Straziota et al
Yu et al41 (2008)
Stonecipher & Kezirian
37
de Ortueta et al36 (2009)
Mastropasqua et al
33
(2008)
Kim et al32 (2004)
Dougherty et al
31
WFG vs Cv
WFO
Schallhorn et al20 (2009)
George et al27 (2010)
WFG
WFO
(2005)
WFG
WFG
Profile
Arbelaez et al28 (2009)
Awwad et al
21
Keir et al23 (2011)
Bottos et al
Study (y)
Overview of the Disparity in Study Design, Surgical Techniques, Excimer Laser Platforms, and
Outcomes Analyzed Among Studies Comparing Different Ablation Profiles
TABLE 1
Wavefront Ablation Profiles/Smadja et al
7
Wavefront Ablation Profiles/Smadja et al
platform has demonstrated a clear superiority over
another. The main reason lies in the difficulties in analyzing and comparing findings among those different
studies. The Table summarizes the disparities in study
design and parameters analyzed among several comparative studies. The lack of standardization in patient
selection, range of attempted correction, excimer laser
platform and ablation algorithm used, nomogram adjustments, and visual function tested (visual acuity,
contrast sensitivity, wavefront errors, or subjective patient satisfaction and visual symptoms) lead to a high
degree of bias and significant discrepancies in the results. Furthermore, over the past 10 years, numerous
improvements in excimer laser platforms such as faster repetition rates, faster eye trackers, and wavefront
analyzers (providing more accurate measurements),
may have led to superior outcomes, inducing more
variables and thus further confusing the critical analysis of the results.
AUTHOR CONTRIBUTIONS
Study concept and design (D.S.); data collection (D.S.); analysis and interpretation of data (D.S., G.R.M., M.R.S., R.R.K.); drafting
of the manuscript (D.S., G.R.M.); critical revision of the manuscript
(M.R.S., R.R.K.); supervision (R.R.K.)
PERSPECTIVES
Despite the technological improvements and improvements in refractive outcomes in terms of induction of higher order aberrations and reduction of night
vision symptoms compared to the standard procedure,17-19 it is now a well known fact that wavefrontguided ablation profiles are not as effective as originally promised. It was demonstrated that wavefront-based
ablation profiles could lead to incomplete correction
of HOAs or induction of additional aberrations, especially when higher refractive corrections are required.
The reason is believed to be due to an inaccurate transfer of a theoretically calculated ablation profile to the
cornea by simplifying the effect of the multi-lens system of the eye. As suggested by Mrochen et al51 only
an individualized eye model, based on an optical ray
tracing algorithm, can provide an ideal ablation profile
by achieving the highest degree of customization.
This eye model is obtained by taking into account
the following parameters: wavefront of the entire eye,
shape and curvature of the anterior and posterior surface of the cornea, corneal and lens thicknesses, anterior chamber depth, axial ocular length, and after
an optimization process, the data related to the lens
surface. Unpublished data collected in the first European multicenter clinical trial on the ray tracing ablation profile demonstrated excellent safety and efficacy
visual outcomes. After 3 months, 75% of eyes gained
one line of CDVA and 5% gained two lines, whereas
no eyes lost lines. These results seem to be promising
and if a clinically significant effect is confirmed, this
ray tracing ablation profile may be able to fulfill the
promise of “super vision.”
6. Bueeler M. Maximum permissible lateral decentration in aberration-sensing and wavefront-guided corneal ablation. J Cataract
Refract Surg. 2003;29(2):257-263.
8
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9
Wavefront Ablation Profiles/Smadja et al
AUTHOR QUERIES
Your repeatedly mention that no algorithm has proven to be superior over another. Please remove all repetitive
statements throughout the paper.
Regarding reference 8, did Dr Artal present a talk at this meeting? Did the author speak during the talk or after?
The following was changed. Okay as edited?
Original: Decreased quality of vision reported by the patient as blurred vision under low light conditions, halos, and glare are the main complaints after conventional excimer laser refractive surgery.13
Edited: The main complaints reported by patients after conventional excimer laser refractive surgery are
blurred vision under low light conditions, halos, and glare, which lead to decreased visual quality.13
Please clarify the following.
Following the company-driven technological developments, several studies comparing different wavefront-guided laser platforms have been published despite the bias introduced such as the familiarization to the
use of a new platform and the need for nomogram adjustment that is surgeon-dependent.
Please clarify the following.
These findings also suggest that the custom-Q profile was not able to deliver exactly the attempted asphericity with the current technology, probably affected also by an unexpected wound healing response.
Please clarify the following.
However, corneal wound-healing response tends to smooth features applied to the corneal stroma and
potentially avoid the effect of the intended ablation to correct HOAs.
Please provide a source and year for the unpublished data in the last paragraph of the article.
In unpublished data collected in the first European multicenter clinical trial on the ray tracing ablation
profile, excellent safety and efficacy visual outcomes were reported. After 3 months, 75% of eyes have gained one
line of CDVA and 5% gained two lines, whereas no eyes lost lines
In the last sentence of the article, “super normal vision” was changed to “super vision,” as used in the Abstract
and Introduction. Okay as edited?
In the Table, Femto was changed to FS laser and MK was changed to keratome. Okay as edited?
10
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