Intracorneal Hydrogel Lenses and Corneal
Aberrations
Jorge L. Alió, MD, PhD; Mohamed Helmy Shabayek, MD, MSc; Robert Montes-Mico, OD, MPhil;
M. Emilia Múlet, MD, PhD; Ahmed Galal Ahmed, MD, MSc; Jesús Merayo, MD, PhD
ABSTRACT
PURPOSE: To investigate the optical performance of
the cornea based on corneal aberrometry following intracorneal hydrogel lens implantation.
METHODS: A retrospective, nonconsecutive, observational study of the anterior corneal surface aberration
profile of four hyperopic eyes previously implanted with
an intracorneal hydrogel lens were studied by videokeratographic elevation maps before and 6 months after
surgery.
RESULTS: Intracorneal hydrogel lenses reduced the
optical performance in all four eyes by increasing the
spherical aberrations by a mean factor of 1.87 and
1.95, coma aberrations by a mean factor of 2.98 and
3.01, and total higher order aberrations by a mean factor of 2.6 and 2.17 at 3.0-mm and 6.5-mm pupils,
respectively (P⬍.005).
CONCLUSIONS: Intracorneal hydrogel lenses decreased
the optical performance of the cornea by significantly
increasing spherical, coma, and total higher order aberrations. [J Refract Surg. 2005;21:247-252.]
S
ynthetic intrastromal implants have been investigated as a refractive surgical procedure for the past
40 years. This technology was first suggested by Barraquer in 1949.1 Assessment of the corneal tissue reaction to
intracorneal hydrogel lenses was first studied in primates2-4
then in humans to prove the biocompatibility of the lens with
the corneal tissue. The implantation of hydrogel intracorneal
lenses in human eyes was initially performed by Werblin et al
in 1992.5 The hydrogel lenses are biocompatible and implantation does not produce a significant physiological disruption. Therefore such devices can be removed or exchanged
with minimal biological consequences. The most important
characteristic of the hydrogel intracorneal lens is permeability, which is similar to the corneal stroma, allowing exchange
of water and nutrients between the posterior and anterior layers of the cornea to maintain normal corneal physiology.2,4,6
However, despite previous reports on the refractive performance of intracorneal hydrogel lenses,4,5,7 once implanted
in the human eye the effects on the finer aspects of optical
performance are basically unknown. In this study, the corneal aberration pattern that results following implantation of
intracorneal hydrogel lenses was evaluated.
PATIENTS AND METHODS
This study comprised four eyes of three patients implanted with intracorneal hydrogel lenses between February and
April 2002. The criteria for selecting these cases included
From the Department of Refractive Surgery, Vissum Instituto Oftalmológico
de Alicante and Division of Ophthalmology, Miguel Hernández University,
Medical School, Alicante, Spain (Alió, Shabayek, Montes-Mico, Múlet,
Ahmed); Research Institute of Ophthalmology, Giza, Egypt (Shabayek,
Ahmed); and Instituto de Oftalmobiologia Aplicada, University of Valladolid,
Spain (Merayo).
This study was supported in part by a grant of the Spanish Ministry of
Health, Instituto Carlos III, Red Temática de Investigación en Oftalmología,
Subproyecto de Cirugía Refractiva y Calidad Visual (C03/13).
The authors have no proprietary interest in the materials presented herein.
Correspondence: Jorge L. Alió, MD, PhD, Instituto Oftalmológico de Alicante,
Avda. Denia, s/n, (Edificio VISSUM) 03016 Alicante, Spain. Tel: 96 5150025;
Fax: 96 5151501; E-mail: jlalio@oftalio.com
Received: April 29, 2004
Accepted: October 6, 2004
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Intracorneal Hydrogel Lenses and Corneal Aberrations/Alió et al
TABLE 1
Preoperative and 6-month
Postoperative Visual Acuity and
Refraction in Four Eyes With
Intracorneal Hydrogel Lenses
Eye
Parameter
1
2
3
4
Preoperative
UCVA
0.4
0.3
0.15
0.2
Sphere (D)
⫹5.50
⫹5.50
⫹3.50
⫹3.50
Cylinder (D)
⫺1.50
⫺1.00
⫺1.75
⫺1.00
Axis (°)
25
155
20
10
SE (D)
⫹4.75
⫹5.00
⫹2.75
⫹3.00
BSCVA
1.0
1.0
0.2
0.6
⫹6.00
⫹6.00
⫹3.00
⫹4.00
5.00
5.00
5.00
5.00
0.6
0.4
0.15
0.6
Sphere (D)
⫹1.00
⫹2.00
⫹3.00
0
Cylinder (D)
⫺1.75
⫺2.00
⫺1.00
⫺1.50
INLAY labeled
power (D)
INLAY diameter
(mm)
6-month
Postoperative
UCVA
Axis (°)
40
130
15
20
SE (D)
⫹0.25
⫹1.00
⫹2.50
⫺0.75
BSCVA
0.9
0.8
0.2
0.8
UCVA = uncorrected visual acuity, SE = spherical equivalent refraction,
BSCVA = best spectacle-corrected visual acuity
complete normal postoperative clinical outcome, no
observable corneal edema or decentration of the intracorneal hydrogel lens, no tear film dysfunction, and
no other complication that would lead to postoperative manipulation of the intracorneal hydrogel lens 6
months postoperatively.
Mean patient age was 47.5⫾16.1 years (range: 24 to
58 years). All eyes were implanted with PermaVision
intracorneal hydrogel lenses (Anamed Inc, Lake Forest,
Calif) following the surgical protocol provided by the
manufacturer. This hydrogel lens has a water content of
⬎70%, a refractive index of 1.37, and a 5-mm diameter.
The intracorneal hydrogel lenses were implanted after
creation of an inferior hinged 8.5-mm corneal flap using the 180-µm head of the M2 microkeratome (Moria,
Antony, France). The corneal flap was centered with
respect to limbus and had a 4-mm hinge. Following
the manufacturer’s indications, a “dry technique” was
used for implantation of the intracorneal hydrogel
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JRS0505ALIO.indd 248
lenses. In such a technique, the interface was not irrigated after the microkeratome cut or after lens implantation. The lenses were placed in the pupil zone
of the stromal bed by means of a specific manual vacuum device provided with the inlay. The postoperative
treatment included 0.3% ofloxacin (Exocin; Allergan,
Madrid, Spain) four times/day combined with tobramycin 0.3% and 0.1% dexamethasone (Tobradex; Alcon Cusí, Barcelona, Spain). These three patients (four
eyes) were selected from a larger cohort of patients
who underwent implantation in 2002 following a strict
protocol approved by the ethical board committee at
our institute.
Preoperative and 6-month postoperative corneal topography maps were obtained using the Orbscan II Slit
Scanning Corneal Topography/Pachymetry System,
version 3.10.27 (Orbtek, Salt Lake City, Utah). Measurements in each eye were repeated until a well-focused and aligned image was obtained. Corneal videokeratographic data were downloaded onto floppy disks
in ASCII files that contained information regarding corneal elevation, curvature, power, and position of the
pupil. The aberrometric wavefront data were fit with
Zernike polynomials up to the sixth order to determine the aberration coefficients, using CT-View Software (Sarver & Associates, Fla) from which the wavefront aberration function was reconstructed. From the
Zernike coefficient, the root-mean-square (RMS) wavefront errors for spherical-like aberrations (fourth-order
component Z14 and the sixth-order component Z06) and
coma-like aberrations (third-order components Z13 and
fifth-order component Z15) were calculated. Because of
the linear independence of the Zernike terms, the higher
order RMS wavefront error was computed by adding all
components (ie, the total RMS error was the square root
of the sum of the squares of the RMS values of the components except astigmatism).
RESULTS
Preoperative and 6-month postoperative visual acuity, refraction, inlay labeled power, and diameter are
shown in Table 1.
As expected, in all four eyes, the RMS value of the
spherical, coma, and total higher order aberrations increased at 3.0-mm and 6.5-mm pupils from before to after
implantation of the intracorneal hydrogel lens (Tables 2
and 3).
The mean difference between pre- and postoperative RMS spherical aberration was 0.185 µm (P⭐.005)
and 0.2140 µm (P⭐.004) for the 3.0-mm and 6.5-mm
pupils, respectively. Similarly, the difference in coma
aberration was 0.0584 µm (P⭐.000) and 0.5652 µm
(P⭐.002) and for total higher order aberrations was
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TABLE 2
Change in Corneal Aberrations (µm) After
Intracorneal Hydrogel Lens Implantation for a 3.0- and 6.5-mm Pupil
3.0-mm Pupil
Eye
1
2
3
4
RMS
(Aberration)
Preoperative
Spherical
0.0227
6.5-mm Pupil
Postoperative
Increasing
Factor (%)
Preoperative
Postoperative
Increasing
Factor (%)
0.0381
167
0.2299
0.5187
225
Coma-like
0.0313
0.0861
275
0.3186
0.8338
261
Higher order
0.0531
0.1229
231
0.5472
1.4731
269
Spherical
0.0229
0.0377
164
0.2414
0.4043
167
Coma-like
0.0318
0.0914
287
0.3678
0.8177
222
Higher order
0.0588
0.1244
211
0.5278
1.1285
213
Spherical
0.0212
0.0395
186
0.2016
0.4039
200
Coma-like
0.0207
0.0817
385
0.2011
0.8067
401
Higher order
0.0424
0.1378
325
0.4291
1.2174
283
Spherical
0.0189
0.0444
234
0.2278
0.4297
188
Coma-like
0.0397
0.0978
246
0.3088
0.9988
323
Higher order
0.0618
0.1879
304
0.5379
1.4759
274
RMS = root-mean-square
0.0892 µm (P⭐.008) and 0.8132 µm (P⭐.002) for the
3.0-mm and 6.5-mm pupils, respectively.
DISCUSSION
Along with refractive outcome, quality of vision is
also important after refractive surgery. The introduction of wavefront science in refractive surgery has
provided a better understanding of the optical performance of the eye following different procedures.
Refractive intracorneal hydrogel lens surgery may be
accompanied by different clinical complications that
may affect overall clinical outcome.7
However, the optical behavior in terms of aberrometry performance of the intracorneal hydrogel lens once
implanted in the human cornea for the correction of
hyperopia has never been reported, hence we are unable to compare our results with any previous data.
The changes in the pattern of corneal aberrations
observed in this study might be caused only by the microkeratome cut or by the presence of the inlay. Porter
et al8 and Pallikaris et al9 studied the aberrations induced by the microkeratome cut and reported that the
microkeratome cut can generate significant but small
increases in higher order aberrations.
In relation to the hyperopic patients evaluated, the
magnitude of preoperative corneal RMS aberration
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JRS0505ALIO.indd 249
appears to lie within normal limits reported for 3.0and 6.0-mm pupil sizes.10 If we consider the results
obtained in corneal aberrations after intracorneal hydrogel lens implantation, an increase was found in the
total higher order aberration terms. Table 2 shows the
change after intracorneal hydrogel lens implantation
for all eyes studied. The Figure shows the change for
all aberrations at both pupil diameters.
According to these data, spherical-like, coma-like,
and total higher order aberrations all increased after
intracorneal hydrogel lens implantation by a factor of
between 1.8 and 3.7 times for both pupil diameters.
The results were statistically significant at the 1% level for both pupil diameters (P⬍.001).
If we consider the results in more detail, changes in
spherical aberration (fourth-order term, Z04) are caused
by shifting the thickness distribution within the cornea followed by a change in corneal surface topography. Intracorneal hydrogel lens implantation creates a
more prolate cornea, thereby inducing a negative shift
in spherical aberration (by mean of ⫻1.87 and ⫻1.94,
3.0- and 6.5-mm pupil, respectively). The total amount
of the spherical aberration changes should depend on
the thickness of the intracorneal hydrogel lens implanted for a particular diameter. Due to the small sample of
cases implanted with intracorneal hydrogel lenses (four
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Intracorneal Hydrogel Lenses and Corneal Aberrations/Alió et al
TABLE 3
Mean Difference of Root-Mean-Square (RMS) Value Preoperatively and
Postoperatively for 3.0- and 6.5-mm Pupils
Aberration
Postoperative
Difference Pre- and
Postoperative
(P value)
0.0214
0.0399
.005
0.0189 to 0.0229 (0.0018)
0.0377 to 0.0444 (0.003)
Preoperative
Spherical
3.0-mm pupil
Range (SD)
6.5-mm pupil
Range (SD)
Difference 3.0- and 6.5-mm (P value)
0.2252
0.4392
0.201 to 0.241 (0.016)
0.4039 to 0.5187 (.05)
.0001
.001
.004
Coma-like
3.0-mm pupil
Range (SD)
6.5-mm pupil
Range (SD)
Difference 3.0- and 6.5-mm (P value)
0.0309
0.0893
0.0207 to 0.0397 (0.007)
0.0817 to 0.0978 (0.006)
0.2991
0.8643
0.201 to 0.367 (0.07)
0.8067 to 0.9988 (0.09)
.004
.0003
0.0540
0.1432
0.0424 to 0.0618 (0.08)
0.1229 to 0.1879 (0.03)
0.5105
1.3237
0.429 to 0.547 (0.05)
1.1285 to 1.4759 (0.17)
.0003
.001
.000
0.002
Total higher order
3.0-mm pupil
Range (SD)
6.5-mm pupil
Range (SD)
Difference 3.0- and 6.5-mm (P value)
eyes), it is not possible to assess a correlation between
preoperative spherical error and induced postoperative
spherical aberration. However, it would be expected
that the increment of spherical aberration would be directly related to the preoperative refraction: the larger
the correction, the larger amount of spherical aberration
induced by intracorneal hydrogel lens implantation.
Comparison of our findings with those reported on
corneal aberrometry changes induced by hyperopic laser in situ keratomileusis (LASIK)10 shows that changes
in spherical aberration are similar between hyperopic
LASIK and intracorneal hydrogel lens implantation for
photopic conditions (3.0-mm pupil). However, some
discrepancies are found when we compare those results
under mesopic conditions (6.5-mm pupil). Wang and
Koch10 found a reduction in spherical aberration after
hyperopic LASIK in contrast to ours (Table 2), which
revealed an increase under photopic conditions. Considering that our results are computed for a 6.5-mm pupil and those of the previous authors10 are for a 6.0-mm
pupil, we believe the difference is due to the different
paracentral region of the cornea between post-hyper250
JRS0505ALIO.indd 250
.008
.002
opic LASIK and intracorneal hydrogel lens implantation. The first has a 6-mm ablation zone and a 9-mm
transition zone, and the intracorneal hydrogel lens has
an optical diameter of 5.00. Therefore, a transition zone
between the ablated and non-ablated cornea is expected
to reduce the change in spherical aberration.
If we consider the changes found in coma-like aberration (Table 2), the mean increasing factor ranged
from 2.94 to 3.71 (3.0-mm and 6.5-mm pupil, respectively). Although the increase in spherical aberration
is systematic, an intereye variability is present in the
amount of coma induced by intracorneal hydrogel
lens implantation. As mentioned earlier for spherical
aberration, we do not have enough data to correlate
the change in coma-like aberration with preoperative
spherical error. However, in contrast to spherical aberration change, coma-like aberration should not correlate with preoperative error in the same way (eg, eye 3,
which required half the correction required for eyes 1
and 2, had a more noticeable increase in coma-like aberration). Compared with hyperopic LASIK, we found
large amounts of coma-like change after surgery. For
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Intracorneal Hydrogel Lenses and Corneal Aberrations/Alió et al
preoperative
postoperative
preoperative
0.16
1.4
0.14
1.2
0.12
1
RMS
0.1
RMS
postoperative
0.08
0.8
0.6
0.06
0.4
0.04
0.2
0.02
0
Spherical
Aberration
Coma-like
Aberration
0
Higher Order
Aberration
3.0-mm Pupil
A
Spherical
Aberration
Coma-like
Aberration
Higher Order
Aberration
6.5-mm Pupil
B
Figure. Mean changes in corneal aberrations (µm) after intracorneal hydrogel lens implantation for a A) 3.0-mm and B) 6.5-mm pupil.
example, Wang and Koch10 found an increasing factor between 1.03 and 1.42 after LASIK and our results
revealed a factor between 2.22 and 4.01 (photopic and
mesopic conditions). They explained the reductions
in coma aberration could be expected from lasers with
eye tracker systems. In fact, they found lower values
in coma using the VISX Star S3 versus the VISX Star
S2 (VISX, Santa Clara, Calif) (eye tracker and non-eye
tracker systems, respectively).
How can we explain our increasing factor in coma
aberration after intracorneal hydrogel lens implantation? We believe that centration of the intracorneal hydrogel lens plays a decisive role in this change. Despite
this fact, we did not observe any decentration clinically. A slight degree of misalignment with respect to
the line of sight, which is used for centration during
topography, and the intracorneal hydrogel lens optical
axis will provoke an increase in this non-rotationally
symmetric aberration.
The effect of simulated pupil dilation, from 3.0- to
6.5-mm, is consistent with previous reports on the effect
of pupil dilation on corneal aberrations.10-13 Although
previous studies reported the effect after photorefractive keratectomy or LASIK procedures, it seems reasonable to attribute the change to the same source when
the pupil dilates in intracorneal hydrogel lens implantation. Those changes between the mid-peripheral region of the cornea induced by intracorneal hydrogel
lens insertion modify the corneal profile, giving a bifocal effect and consequently an increase of the corneal
aberration when large pupils are considered.14
Intracorneal hydrogel lens implantation increases
higher order corneal aberrations. In coma-like aberration, improvements in intracorneal hydrogel lens
centration could aid postoperative optical quality. The
change in spherical aberration, which is greater folJournal of Refractive Surgery Volume 21 May/June 2005
JRS0505ALIO.indd 251
lowing intracorneal hydrogel lens implantation than
LASIK surgery, is probably a function of the intended
cornea steepening and the flattening of the mid-peripheral region. Modifying the peripheral form of the
intracorneal hydrogel lens (eg, choosing an aspheric
design), could improve the optical quality of the postoperative surface.
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