Download - Journal Of Emmetropia :: Home

ARTICLE
Four-year Follow-up of Intrastraomal Corneal Ring
Segments in Patients with Keratoconus
Jose L. Güell, MD1,2,3, Merce Morral, MD1,4, Cecilia Salinas, MD1, Daniel Elies, MD1,
Oscar Gris, MD1, Felicidad Manero, MD1
PURPOSE: To report long-term efficacy and safety of Intacs intracorneal ring segments
(ICRS) in mild to moderate keratoconus.
SETTING: Instituto Microcirugia Ocular (IMO), Barcelona, Spain.
METHODS: Retrospective case series. Intacs ICRS were implanted to 46 eyes of 36
patients with keratoconus who exhibited intolerance to contact lenses. Manifest refraction,
uncorrected visual acuity (UCVA) and best-spectacle corrected visual acuity (BSCVA), keratometry (K), biomicroscopy, applanation tonometry, and funduscopy were performed
before surgery, at 3 months and at yearly intervals up to 5 years. Intraoperative and postoperative complications were also recorded.
RESULTS: Intacs implanted were: 2 symmetric segments (19(41.3%)eyes), 2 segments of
different thickness (23(50%)eyes), and one segment implanted inferiorly (2(4.34%) eyes).
Mean spherical equivalent (SE) improved from –3.50±2.84D to –0.5±1.48D. Mean refractive cylinder was –2.68±1.7D preoperatively, and –2.9±1.7D, postoperatively. Mean K
decreased from 46.14±3.42 to 44.35±3.66 D. UCVA improved in 43 (93.4%) eyes, and
BSCVA remained stable or improved in 38 (82.6%) eyes. Eight (17.4%) eyes lost 1 line of
BSCVA. Both BSCVA and SE refraction improved progressively during the first 6 months,
and remained stable over the 4-year follow-up period. Cylinder results were unpredictable.
No intraoperative complications occurred. One eye required penetrating keratoplasty due
to unexplained loss of BSCVA one year after Intacs implantation.
CONCLUSIONS: Over a 4-year follow-up period, ICRS have been effective to improve
UCVA, BSCVA and SE in eyes with keratoconus. Intacs implantation may be an option to
delay penetrating keratoplasty in keratoconic patients who become contact lens intolerant.
J Emmetropia 2010; 1: 9-15
INTRODUCTION
Several surgical strategies have been proposed to
improve visual function in patients with keratoconus
who become contact lens intolerant1,2. In mild-toSubmitted: October 20, 2009
Revised: March 15, 2010
Accepted: March 26, 2010
1
Instituto de Microcirugia Ocular (IMO), Barcelona, Spain.
Associate professor of Ophthalmology at Universitat Autonoma
de Barcelona, Barcelona, Spain
3 Director of the Cornea and Refractive Surgery Unit, Instituto
Microcirugia Ocular, Barcelona, Spain.
4 Institut Clínic d’Oftalmologia (ICOF), Hospital Clinic i
Provincial de Barcelona, Barcelona, Spain.
2
Corresponding author: Jose Luis Güell, Instituto de Microcirugia
Ocular (IMO), c/Munner 10, 08022 Barcelona, Spain. E-mail:
[email protected], [email protected]
© 2010 SECOIR
Sociedad Española de Cirugía Ocular Implanto-Refractiva
moderate keratoconus, when the central cornea
remains clear, intrastromal corneal ring segments
(ICRS), and phakic intraocular lenses (PIOLs) may
provide enough BSCVA, and sometimes uncorrected
visual acuity (UCVA), to postpone and sometimes
avoid the need for corneal transplantation. To stop the
progression of the disease, these refractive procedures
may be combined with collagen cross-linking (CCL) in
cases of progressive keratoconus, which may grant a
more sustained result3-6.
ICRS improve quality of vision and visual acuity
through a dual effect. Not only do they correct myopic
spherical equivalent, but they also improve topographic abnormalities by recentering the corneal optical
zone7-13. However, their role on ectasia stabilization
remains unclear.
Long-term follow-up is specially important in the
case of keratoconus because if ectasia were to progress,
ISSN: 2171-4703
9
10
IMPLANTABLE COLLAMER LENS FOR LOW MYOPIA
the refractive correction achieved with the ICRS would
be at least partially lost. In this study, we present fouryear follow-up data of IntacsTM (Addition Technology
Inc., Sunnyvale, CA, USA) ICRS implanted in mildto-moderate keratoconus with signs of topographic and
refractive progression, without the use of CCL.
PATIENTS AND METHODS
This study included 46 eyes of 36 patients with
Keratoconus stage I-II of Krumeich’s classification14 who
where contact lens intolerant and showed topographic
and refractive progression during the six months previous to IntacsTM surgery. Thirty-one (67.39%) eyes of 21
(58.33%) patients were seeking refractive surgery and
keratoconus was diagnosed when preoperative topography was performed. Ten of these patients had bilateral
implantation, whereas 11 had unilateral implantation, as
the fellow eye was stable or did not require refractive correction. Fifteen (41.66%) eyes of 15 patients with
known keratoconus had previously undergone penetrating (PKP) or deep anterior lamellar keratplasty (DALK)
in the fellow eye due to severe keratoconus, and had unilateral Intacs implantation. Eleven (23.9%) eyes were
implanted IntacsTM with the aim to recenter and regularize corneal topography, so as to enable further refractive correction either with contact lenses or phakic
intraocular lenses (PIOLs). All patients were fully
informed about the details and possible risks of the specific procedure, together with alternative refractive techniques and their respective benefits and risks. Written
informed consent was obtained from all patients before
surgery in accordance with the Declaration of Helsinki,
and the study was approved by the ethics committee of
our institution, Instituto de Microcirugia ocular, and the
Universitat Autonoma de Barcelona. All the eyes were
operated by the same surgeon (JLG).
Preoperative examination and follow-up
The patients underwent a complete preoperative
ophthalmologic examination, including manifest refraction, Snellen’s best-spectacle corrected visual acuity
(BSCVA), uncorrected visual acuity (UCVA), applanation tonometry, corneal topography (Orbscan. Bausch
and Lomb. Rochester, NY, USA), ultrasound pachymetry (DGH 500 Pachymeter, DGH Technology, Inc,
Exton, PA, USA), and a fundus examination.
Postoperative follow-up visits were held at 24 hours, 3
and 6 months, and at yearly intervals up to four years. The
long-term study results evaluated were UCVA, BSCVA,
predictability and stability of refractive correction, efficacy
(ratio between the mean postoperative UCVA and the
mean preoperative BSCVA) and safety index (ratio
between the mean postoperative BSCVA and the mean
preoperative BSCVA). Complications were also recorded.
Inclusion and exclusion criteria
Inclusion criteria were: contact lens intolerant
patients with mild-to-moderate Kc (Krumeich’s stage I
or II)14 with topographic and/or refractive signs of progression for the previous 6 months; central pachymetry
>400 µm; clear central cornea; minimum follow-up of
4 years. Spherical equivalent (SE) was not a limitation.
Exclusion criteria were: eyelid abnormalities,
untreated lid margin disease, or tear film abnormalities;
history of herpetic eye disease; presence of central or
paracentral corneal leucoma; intraocular pressure
>21 mmHg or glaucoma; preexisting macular pathology or abnormal retinal condition; systemic diseases (e.g.,
autoimmune disorder, connective tissue disease, atopia,
diabetes mellitus, or Stevens-Jonhson Syndrome); central corneal thickness of less than 400 µm; scotopic
pupil diameter greater than 7 mm.
Surgical Procedure
The nomogram for IntacsTM inserts selection is
depicted in table 1. The thickness of the ICRS to be
implanted was selected on the basis of preoperative
SE. In those cases with higher degrees of myopic SE,
the thickest segments (450 µm) were used. If the cone
was not central, corneal pachymetry at the site of incision and segment implantation was checked preoperatively.
Surgical technique has been extensively
described8,10. In the eyes with inferior or central cone,
we place the incision at 90°. The segments are placed
nasally and temporally, and pushed until the inferior
extremes contact with each other, as if they were
embracing the cone, in an attempt to push up the cone.
With this approach, the two segments act as if they
were a whole inferior segment of 280°. In the eyes with
oblique corneal astigmatism, two inserts of different
thickness were implanted through an incision placed at
the flattest meridian. The thickest segment was placed
inferiorly, in the steepest axis. In those cases where the
SE was lower than –0.5 D, a single inferior segment
was implanted.
Table 1. Nomogram for Intacs inserts selection for the
correction of myopia
Intacs thickness (mm)
Spherical Equivalent (D)
0.21
0.25
0.30
0.35
0.40
0.45
–0.75 to –0.975
–1.00 to –1.625
–1.75 to –2.25
–2.315 to –3.00
–3.125 to –3.75
–3.875 to –4.50
mm: milimeters; D: Diopters.
JOURNAL OF EMMETROPIA - VOL 1, JANUARY-MARCH
IMPLANTABLE COLLAMER LENS FOR LOW MYOPIA
11
Statistical analysis
Microsoft Excel (Redmond, WA, USA) was used
for compilation of data and to perform descriptive statistics. All variables were analyzed preoperatively, and
postoperatively, at 3 and 6 months, and at yearly intervals up to 4 years.
Continuous variables were described with mean,
standard deviation (SD) and range (maximum and
minimum value). Comparison of pre and postoperative
data was performed with the paired two-tailed t test.
The threshold of statistical significance was defined as
p≤0.05. The percent of eyes with BSCVA and
UCVA≥20/25 and ≥20/40 at each milestone of followup were also recorded. Efficacy and safety indexes were
calculated for each postoperative interval.
RESULTS
A total of 46 eyes of 36 patients that met the
inclusion criteria were implanted the IntacsTM inserts.
All eyes were available for examination at the 4-year
follow-up visit. Mean age was 28.45±7.7 (range 16 to
53 years of age). Two symmetrical inserts were
implanted through an incision centered at 90° in 19
(41.3%) eyes (Figure 1) with the inferior extremes in
contact with each other, two inserts of different thickness were implanted through an incision placed at the
flattest meridian in 23 (50%) eyes, and a single inferior segment was implanted in 2 (4.34%) eyes. Intacs
thicknessess were as follows: 210 microns (n=2), 250
microns (n=5), 300 microns (n=5), 350 microns
(n=5), 400 microns (n=8) and 450 microns (n=21).
Figure 1. Symmetric implantation of two Intacs inserts (450 Ìm
thickness) in a patient with subclinical keratoconus. (A) Preoperative
topography shows corneal thinning and increased posterior corneal
elevation. (B) Intracorneal rings induce flattening of the anterior
surface of the cornea that results in myopia correction. (C) Clinical
photograph. The segments are placed nasally and temporally, and
pushed until the inferior extremes contact with each other, as if they
were embracing the cone. (D) Anterior segment OCT (Visante)
showing the position of the segments in the posterior stroma.
Figure 2. Mean spherical equivalent and cylinder at each milestone
of follow-up up to 4 years for all groups.
Refractive outcome stability and keratometry
Mean preoperative spherical equivalent (SE) was 3.50±2.84 (range, +1.00 to –15.0 D), and mean preoperative cylinder was –2.68±1.7 (range, 0 to –7 D). Four
years postoperatively, mean SE and cylinder were
–0.5±1.48 (range, –1.5 to –6) and –2.9±1.7 (range,
–1.5 to –6), respectively. At 4 years, mean keratometry
had decreased from 46.14±3.42 to 44.35±3.66.
Figure 2 shows spherical equivalent and cylinder at
each milestone of follow-up up to 4 years for all groups,
and figure 3 shows evolution of spherical equivalent for
each group separately. SE was significantly reduced
compared to preoperative values (paired t test; p<0.05),
and there were no significant changes in SE throughout
the follow-up period (paired t Test; p>0.05), which
shows excellent stability of the SE refractive correction
during the first 4 years of follow-up. Intacs implantation had no significant effect on refractive cylinder
when compared to preoperative values, and there were
no significant changes throughout the follow-up period
(paired t test; p>0.05). Table 2 summarizes refractive
and visual results for each thickness of Intacs segments.
Figure 3. Mean spherical equivalent at each milestone of follow-up
up to 4 years for each group separately.
Visual Acuity, Efficacy and Safety
Figure 4 shows mean UCVA and BSCVA at each
milestone of follow-up. Preoperatively, 32 (69.56%) and
8 (17.39%) of the eyes presented BSCVA≥20/40 and
BSCVA≥20/20, respectively. UCVA was <20/40 in all
(100%) of the eyes. A progressive improvement of
UCVA throughout the follow-up period was noticed,
being most remarkable during the first 6 months. Four
years postoperatively, 30 (65.21%) eyes presented
JOURNAL OF EMMETROPIA - VOL 1, JANUARY-MARCH
12
IMPLANTABLE COLLAMER LENS FOR LOW MYOPIA
Table 2. Preoperative and postoperative refraction and visual acuity for each Intacs inserts thickness
210 µm
Number of eyes
2
SE pre (D)
–1.63±0.17
SE 4y (D)
–1.68±0.17
BSCVA pre
0.65±0.21
UCVA 4y
0.4±0.42
BSCVA 4y
0.7±0.28
Efficacy Index
0.61
Safety Index
1.07
Exchange/Extraction
0
250 µm
300 µm
350 µm
400 µm
450 µm
5
–1.15±0.99
–2.88±4.1
0.68±0.17
0.61±0.02
0.65±0.17
0.89
0.95
0
5
–1.5±1.55
–1.37±0.53
0.62±0.16
0.3±0.28
0.62±0.02
0.48
1
0
5
–1.6±1.26
–0.38±0.53
0.52±0.19
0.35±0.21
0.65±0.07
0.67
1.25
0
8
–2.93±1.5
–0.63±2.37
0.63±0.18
0.53±0.25
0.63±0.15
0.84
1
1/0
21
–5.38±2.7
–0.4±1.77
0.68±0.26
0.56±0.15
0.74±0.17
0.82
1.08
0/2
SE: spherical equivalent; y: years; D: diopters; pre: preoperative; UCVA: uncorrected visual acuity; BSCVA: best-spectacle corrected visual acuity.
UCVA≥20/40, and none of the eyes presented
UCVA≥20/20. BSCVA was ≥20/40 in 38 (82.6%) eyes,
and ≥20/20 in 6 (13.04%) eyes.
UCVA significantly improved in 43 (93.4%) of eyes,
and worsened in 3 (6.6%) of eyes. BSCVA improved in
7 (15.21%) eyes, remained unchanged in 31 (67.31%)
eyes, and worsened in 8 (17.39%) eyes (Figure 5).
BSCVA did not significantly change throughout the follow-up period (t test; p>0.05). At 4 years, overall efficacy and safety indexes were 0.8 and 1.1, respectively.
uneventful. In 11 (23.9%) cases, IntacsTM implantation was performed even though preoperative SE was
greater than –4.5 D, with the aim to recenter the
corneal optical zone and regularize corneal topography.
One patient was successfully readapted to soft contact
lens use, one eye of another patient underwent PRK
over Intacs, and both eyes of another patient underwent toric phakic iris-claw Artisan (Ophtec B.V.,
Groningen, The Netherlands) intraocular lens (IOL)
implantation to correct the remaining refractive error.
Adjustability of the refractive result
Complications
IntacsTM inserts of 400 microns were exchanged for
thicker segments of 450 microns in one (2.1%) eye due
to unexpected undercorrection. Exchange surgery was
No intraoperative complications occurred. Two eyes
(4.3%) required repositioning of a segment that had
been implanted too deeply in the corneal stroma. Four
months after Intacs implantation, one patient had lost
6 lines of BSCVA, even though no clinical complication was observed. Intacs were explanted and penetrating keratoplasty was performed uneventfully. A hyperopic shift occurred in the patient that underwent PRK
over Intacs due to severe epithelial hyperplasia in the
mid-periphery of the cornea, that acted as a negative
lens. Finally, one eye presented with aseptic infiltration
Figure 4. Mean uncorrected and best-spectacle corrected visual
acuity at each milestone of follow-up.
Figure 5. Percentage of eyes that improved, maintained or worsened uncorrected and best-spectacle corrected visual acuity after
Intacs implantation.
Figure 6. Clinical photograph of Intacs combined with Artisan
toric phakic intraocular lens implantation to correct myopic astigmatism in a patient with keratoconus.
JOURNAL OF EMMETROPIA - VOL 1, JANUARY-MARCH
IMPLANTABLE COLLAMER LENS FOR LOW MYOPIA
13
Figure 7. (A) Aseptic infiltration of the
intrastromal channel one month after
surgery probably related to underlying
rosacea that was diagnosed postoperatively. (B) Being topical medical treatment unsuccessful, one of the inserts
had to be explanted. No loss of bestspectacle corrected visual acuity
occurred.
of the intrastromal channel one month after surgery
that required the extraction of one of the inserts. This
infiltration was probably related to underlying rosacea
that was diagnosed postoperatively (Figure 7).
DISCUSSION
It is well known that BSCVA with spectacles is
often unsatisfactory in patients with KC, specially
when anisometropia and high astigmatism is present15,16. Although RGPCL may provide better BSCVA
even if significant irregular astigmatism is present17-19,
27% of chronic CL users become intolerant1,2. In such
circumstances, surgical intervention is required to
achieve optimal visual rehabilitation.
The indications for Intacs inserts in keratoconic eyes
are contact lens intolerant patients, with clear cornea
and central pachymetry greater than 400 microns. In
the case of peripheral conus or pellucid marginal degeneration, where the greatest thinning occurs in the
periphery of the cornea, pachymetry in the site of Intacs
implantation should be checked preoperatively to avoid
perforation into the anterior chamber or immediate or
late extrusion of the segments. At least 100 microns of
posterior stroma under the ring should be left.
Data on long-term follow-up of IntacsTM implantation in keratoconus is scarce. There is only one report
that included 17 keratoconic eyes that were followed for
5 years after IntacsTM implantation20. Being keratoconus
a primary ectasia that may progress, long-term follow-up
data is essential to stablish if Intacs’ effect remains stable
over time. Unfortunately, not only there is a wide variety
of evolutive patterns, but also a large number of eyes do
not show any signs of evolution even though no surgical
procedure is performed. These factors limit the evaluation of the effect of IntacsTM implantation itself.
This case series included 46 eyes with mild-tomoderate keratoconus that had shown topographic
and/or refractive signs of progression before IntacsTM
implantation. If the ectasia had progressed, refraction,
keratometry and visual acuity would have changed
over time. In our group of patients, both refraction
and keratometry have remained stable over the 4 years
of follow-up. The question remains if their refraction
would have remained stable without surgery anyway.
The lack of a control group is a clear limitation of this
study. Therefore, the role of ICRS in stopping the
progression of keratoconus remains controversial.
Some authors have proposed UV-A irradiationinduced corneal collagen cross-linking (CCL) as a first
step to stop the progression of keratoconus, and then
correct the remaining refractive errors with a different
approach, excimer laser corneal surgery or phakic IOL
implantation3-6,21. CCL performed after Intacs implantation in keratoconic eyes has provided better results
and has a more logical rationale than Intacs insertion
alone as evidenced by greater reductions in manifest
cylinder and keratometry readings. A simple additive
effect of both procedures in flattening the central cornea
and a greater local rigidity across the Intacs segment
may account for this synergistic effect22. Kamburoglu et
al. performed CCL one day and 1 month after Intacs
implantation in both eyes of a patient that exhibited
secondary ectasia after LASIK23. However, taking into
account that the refractive effect after ICRS implantation may take several weeks or months, leaving some
time before CCL is performed after Intacs implantation
may be a better strategy than performing CCL immediately after Intacs surgery. From our point of view, CCL
is ideally indicated as soon as any sign of progression is
detected or when the corneal shape improvement stops.
Coskunseven et al. compared the effect of CCL followed by ICRS implantation and ICRS implantation
followed by CCL and found that implantation of ICRS
followed by CCL resulted in greater improvement in
CDVA, SE, and mean K in a group of patients with keratoconus. Mean interval between procedures was 7
months in both groups24.
Similar to previous studies in both myopia correction25,26 and keratoconus20,27, both spherical equivalent and UCVA improve progressively during the first
6 months and then have a steady evolution, as long as
the corneal ectasia remains stable. On the other hand,
Intacs implantation in keratoconic eyes may provide
unexpected refractive cylinder and visual results. In
some cases, the topography recentering with improvement of the I-S ratio and irregular astigmatism is not
accompanied with an improvement in UCVA and/or
BSCVA. In others, UCVA and BSCVA significantly
improve even though the refractive cylinder error
JOURNAL OF EMMETROPIA - VOL 1, JANUARY-MARCH
14
IMPLANTABLE COLLAMER LENS FOR LOW MYOPIA
remains almost unchanged due to the regularization of
the topography. The reason of these unexpected results
remains unknown. Ultrastuctural variability of the
corneal stroma of different patients with keratoconus
or different genetic basis may be some reasons for this
phenotipic variability after Intacs implantation, even
though the topography or refraction may be similar.
Generally, a trend towards undercorrection is recommended, as the same Intacs thickness has a greater
effect in thinner corneas27. Nevertheless, being an
adjustable and reversible technique, Intacs may be
removed or exchanged for a thicker or thinner one in
case the refractive result obtained is not the desired9.
Moreover, in case penetrating or deep anterior lamellar
keratoplasty is needed, trephination of the recipient
cornea may be performed uneventfully and the midperipheral cut in presence of the segments may be more
homogeneous and perpendicular to the corneal surface.
In our study, we observed that thicker segments
showed better refractive and visual results than the
thinner ones. Although the small number of patients in
each group did not allow reliable comparisons, thicker
segments may induce a higher change in the distribution of the corneal tissue than thinner segments, which
may account for this better result.
IntacsTM inserts only correct a limited range of
myopia, and high refractive errors commonly seen in
patients with keratoconus may remain. Intacs implantation is first performed to recenter the topography and
decrease irregular astigmatism and, then, residual
refractive errors may be corrected with spectacles or
soft contact lenses28. Also, TPIOLs have been implanted after ICRS, as we did in one of the patients of this
series, and some other later on29-31.
Several nomograms have been proposed for Intacs
implantation in keratoconic eyes: same-thickness inferior and superior segments, a single inferior segment,
thicker inferior and a thinner superior segments,
etc…32-36 However, there is lack of scientific evidence
in terms of prospective, comparative, randomized studies that demonstrate the superiority of one approach
over the other. Sharma et al. compared the effect of
implanting a single inferior segment vs two segments in
peripheral cones, obtaining better visual and keratometric results when a single inferior segment was
inserted. According to this author, single segments
induced localized flattening inferiorly and steepening
in the upper cornea, which leads to a greater decrease
in I-S ratio37. Our preferred approach has been to place
the segments through an incision in the flattest meridian, pushing them until the inferior extremes contact
with each other, as if they were embracing the cone.
With this approach, the inserts act as an only inferior
segment of 280°, and the inferior cone is «elevated»,
with similar effects in decreasing I-S ratio and recentering the topography.
Ocular infection is a serious complication of refractive surgery and may lead to a significant reduction in
visual acuity. The incidence of infectious keratitis after
IntacsTM implantation is low (0.2%25 and 0.63%38).
Apart from those microorganisms frequently found in
ocular infections such as gram positive aerobic bacteria
(e.g. Staphylococcus epidermidis), anaerobic bacteria
have also been reported as a cause of infectious keratitis after Intacs implantation. The anaerobic conditions
in the intrastromal channel may predispose to the
development of the anaerobic infection39-41. Although
infections usually appear within 3 weeks after surgery25,38,39, late bacterial keratitis has also been reported40,41. In some cases topical antibiotics alone are ineffective and channel irrigation with antibiotics and
Intacs extraction are required.
Aseptic inflammatory reaction inside the intrastromal channel has also been described after Intacs implantation, especially in patients with atopia or keratoconus42. One of our patients presented with aseptic infiltration of the nasal intrastromal channel on the right eye
one month after surgery that required the extraction of
one of the inserts. This infiltration was probably related
to underlying rosacea that was diagnosed postoperatively. Differencial diagnosis with an infectious ethiology is
not always straightforward. In fact, we first suspected
infectious keratitis, and irrigation of the channel with
balanced salt solution for the collection of microbiological samples followed by irrigation with ceftazidime was
performed at the onset of symptoms. Microbiological
workout did not show any microorganism and the
patient only improved after the nasal segment was taken
out and topical steroids were started. Rau et al reported
a prevalence of corneal infiltrates of 13.3%43. Immediate
treatment of such infiltrates is mandatory to prevent irreversible adverse effects on visual acuity.
In conclusion, this study shows that Intacs
implantation in mild to moderate keratoconus provides stable refractive and topographic results, and
improves UCVA and BSCVA in the majority of
patients. However, our knowledge on how and when
Intacs segments will be effective in keratoconic eyes
is still limited. A longer follow-up and prospective,
comparative, randomized clinical trials are still needed to stablish their role in the stabilization of the
ectasia.
REFERENCES
1. Espana EM, Tseng SC. Analysis of contact lens intolerance by
exploring neuroanatomic integration of ocular surface defense.
Cont Lens Anterior Eye 2003; 26: 131-7.
2. Glasson MJ, Stapleton F, Keay L, et al. Differences in clinical
parameters and tear film of tolerant and intolerant contact lens
wearers. Invest Ophthalmol Vis Sci 2003; 44: 5116-24.
3. Wollensak G. Crosslinking treatment of progressive keratoconus: new hope. Curr Opin Ophthalmol 2006; 17: 356-60.
JOURNAL OF EMMETROPIA - VOL 1, JANUARY-MARCH
15
IMPLANTABLE COLLAMER LENS FOR LOW MYOPIA
4. Wollensak G, Spoerl E, Seiler T. Riboflavin/ultraviolet-ainduced collagen crosslinking for the treatment of keratoconus. Am J Ophthalmol 2003; 135: 620-7.
5. Caporossi A, Baiocchi S, Mazzotta C, et al. Parasurgical therapy for keratoconus by riboflavin-ultraviolet type A rays
induced cross-linking of corneal collagen: preliminary refractive results in an Italian study. J Cataract Refract Surg 2006;
32: 837-45.
6. Tan DT, Por YM. Current treatment options for corneal ectasia. Curr Opin Ophthalmol 2007; 18: 284-9.
7. Holmes-Higgin DK, Burris TE. Corneal Surface Topography
and associated visual performance with Intacs for myopia:
phase III clinical trials results. The Intacs Study Group.
Ophthalmology 2000; 107: 2061-71.
8. Schanzlin DJ, Asbell PA, Burris TE, Durrie DS. The intrastromal corneal ring segments; phase II results for the correction
of myopia. Ophthalmology 1997; 104: 1067-1078.
9. Pokroy R, Levinger S. Intacs adjustment surgery for keratoconus. J Cataract Refract Surg 2006; 32: 986-992.
10. Colin J. European clinical evaluation: use of Intacs for the
treatment of keratoconus. J Cataract Refract Surg 2006; 32:
747-755.
11. Colin J, Cochener B, Savary G, Malet F. Correcting keratoconus with intracorneal rings. J Cataract Refract Surg 2000;
26: 1117-1122.
12. Colin J, Cochener B, Savary G, et al. INTACS inserts for
treating keratoconus; one-year results. Ophthalmology 2001;
108: 1409-1414.
13. Siganos D, Ferrara P, Chatzinikolas K, et al. Ferrara intrastromal corneal rings for the correction of keratoconus. J Cataract
Refract Surg 2002; 28: 1947-1951.
14. Krumeich JH, Daniel J, Knülle A. Live-epikeratophakia for
keratoconus. J Cataract Refract Surg. 1998; 24: 456-63.
15. Pesudovs K, Garamendi E, Elliott DB. A quality of life comparison of people wearing spectacles or contact lenses or having undergone refractive surgery. J Refract Surg 2006; 22(1):
19-27.
16. Wietharn BE, Driebe WT Jr. Fitting contact lenses for visual
rehabilitation after penetrating keratoplasty. Eye Contact Lens
2004; 30(1): 31-3.
17. Riddle HK, Parker DA, Price FW. Management of postkeratoplasty astigmatism Curr Opin Ophthalmol 1998; 9: 15-28.
18. Chastang PJ, Borderie VM, Carvajal-Gonzalez S, et al.
Prediction of spectacle-corrected visual acuity using videokeratography. J Refract Surg 1999; 15: 572-9.
19. Speaker MG, Cohen EJ, Edelhauser HF, et al. Effect of gaspermeable contact lenses on the endothelium of corneal transplants. Arch Ophthalmol 1991; 109: 1703-6.
20. Kymionis GD, Siganos CS, Tsiklis NS, et al. Long-term follow-up of Intacs in keratoconus. Am J Ophthalmol. 2007;
143: 236-244.
21. Kanellopoulos AJ, Binder PS. Collagen cross-linking (CCL)
with sequential topography-guided PRK: a temporizing alternative for keratoconus to penetrating keratoplasty. Cornea
2007; 26: 891-5.
22. Chan CCK, Sharma M, Boxer Wachler BS. Effect of inferiorsegment Intacs with and without C3-R on keratoconus. J
Cataract Refract Surg 2007; 33: 75-80.
23. Kamburoglu G, Ertan A. Intacs implantation with sequential
collagen cross-linking treatment in postoperative LASIK ectasia. J Refract Surg 2008; 24: S726-9.
24. Conskunseven E, Jankov MR 2nd, Hafezi F, et al. Effect of
treatment sequence in combined intrastromal corneal rings
and corneal collagen crosslinking for keratoconus. J Cataract
Refract Surg 2009; 35: 129: 2084-91.
25. Rapuano CJ, Sugar A, Koch DD, et al. Intrastromal Corneal
Ring Segments for Low Myopia. A report by the American
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
Academy of Ophthalmology. Ophthalmology 2001; 108:
1922-1928.
Ruckhofer J, Stoiber J, Alzner E, et al. One year results of
European multicenter study of intrastromal corneal ring segments. Part I: Refractive Outcomes. J Cataract Refract Surg
2001; 27: 277-86.
Alio JL, Shabayek MH, Belda JI, et al. Analysis of results related to good and bad outcomes of Intacs implantation for keratoconus correction. J Cataract Refract Surg 2006; 32: 756-61.
Ucakhan OO, Kanpolat A, Ozdemir O. Contact lens fitting
for keratoconus after Intacs placement. Eye contact lens 2006;
32: 75-77.
Kamburoglu G, Etan A, Bahadir M. Implantation of Artisan
toric phakic intraocular lens following Intacs in a patient with
keratoconus. J Cataract Refract Surg 2007; 33: 528-530.
Colin J, Velou S. Implantation of Intacs and a refractive
intraocular lens to correct keratoconus. J Cataract Refract Surg
2003; 29: 832-34.
Coskunseven E, Onder M, Kymionis GD, et al. Combined
Intacs and posterior chamber toric implantable collamer lens
implantation for keratoconic patients with extreme myopia.
Am J Ophthalmol 2007; 144: 387-389.
Boxer Wachler BS, Christie JP, et al. Intacs for keratoconus.
Ophthalmology 2003; 110: 1031-40.
Chan CC, Wachler BS. Reduced best spectacle-corrected
visual acuity from inserting a thicker Intacs above and thinner Intacs below in keratoconus. J Refract Surg 2007; 23:
93-5.
Siganos CS, Kymionis GD, Kartakis N, et al. Management of
keratoconus with Intacs. Am J Ophthalmol 2003; 135: 64-70.
Alio JL, Shabayek MH. Intracorneal asymmetrical rings for
keratoconus: where should the thicker segment be implanted?
J Refract Surg 2006; 22: 307-9.
Alio JL, Artola A, Hassanein A, et al. One or 2 Intacs segments
for the correction of keratoconus. J Cataract Refract Surg
2005; 31: 943-53.
Sharma M, Boxer Wachler BS. Comparison of single-segment
and double-segment Intacs for keratoconus and post-LASIK
ectasia. Am J Ophthalmol 2006; 141: 891-5.
Ruckhofer J, Stoiber J, Alzner E, et al. One year results of
European multicenter study of intrastromal corneal ring segments. Part II: complications, visual simptoms and patient satisfaction. J Cataract Refract Surg 2001; 27: 287-96.
Bourcier T, Borderie V, Laroche L. Late bacterial keratitis after
implantation of intrastromal corneal ring segments. J Cataract
Refract Surg 2003; 29: 407-409.
Hofling-Lima AL, Branco BC, Romano AC, et al. Corneal
infections after implantation of intracorneal ring segments.
Cornea 2004; 23(6): 547-9.
Shehadeh-Masha’our R, Modi N, Barbara A, et al. Keratitis
after implantation of intrastromal corneal ring segments. J
Cataract Refract Surg 2004; 30: 1802-4.
McAlister JC, Ardjomand N, Ilari L, et al. Keratitis after intracorneal ring segment insertion for keratoconus. J Cataract
refract Surg 2006; 32: 676-8.
Rau M, Dausch D. Intrastromal corneal ring implantation for
the correction of myopia: 12-month follow-up. J Cataract
Refract Surg. 2003; 29: 322-8.
JOURNAL OF EMMETROPIA - VOL 1, JANUARY-MARCH
First author:
José L. Güell, MD
Director of the Cornea and Refractive
Surgery Unit, Instituto de Microcirugía
Ocular (IMO), Barcelona, Spain