Analise das alterações na tomografia da Córnea pós implante de Anel de Ferrara e a correlação destas alterações aos resultados visuais obtidos.

1. 110 Copyright © SLACK Incorporated
O R I G I N A L A R T I C L E
eratoconus is a progressive corneal ectatic disease
characterized by paraxial stromal thinning and
weakening, resulting in irregular astigmatism, cor-
neal protrusion, and distortion of the anterior corneal surface.
It is usually bilateral, although asymmetrical in most cases.1,2
Intrastromal corneal ring segments (ICRSs) are polymethyl-
methacrylate devices successfully used for the management of
keratoconus,3-7
pellucid marginal degeneration,8
postoperative
corneal ectasia,9,10
myopia,11
and high astigmatism after kera-
toplasty. This alternative to keratoplasty is safe and reversible
and does not affect the central visual axis of the cornea. The
goal of ICRS implantation is to improve visual acuity by regu-
larization of the anterior cornea surface.
The aim of the current study was to analyze and compare
the changes that occur to the anterior and posterior corneal
surfaces, which were evaluated using a Scheimpflug imaging
system (Pentacam version 1.20r10; Oculus Optikgeräte GmbH,
Wetzlar, Germany) after Ferrara ICRS (AJL, Boecillo, Spain) im-
plantation. The correlation between these corneal changes and
the visual outcome was also investigated.
PATIENTS AND METHODS
This retrospective and nonrandomized study comprised
consecutive patients with keratoconus who underwent Ferr-
ara ICRS implantation from 2006 to 2009. According to the te-
nets of the Declaration of Helsinki, all patients were informed
of the advantages and risks of the surgical procedure and gave
their consent for their clinical information to be included
KABSTRACT
PURPOSE: To analyze and compare changes to the
anterior and posterior corneal surfaces after Ferrara
intracorneal ring segment (ICRS) (AJL, Boecillo, Spain)
implantation and to correlate those changes with visual
outcomes.
METHODS: This retrospective case series study com-
prised consecutive patients with keratoconus implanted
with the Ferrara ICRS. Computed tomography scans of
the two corneal surfaces were obtained preoperatively
and postoperatively with a rotating Scheimpflug imaging
system. The Wilcoxon test was used to compare groups,
and the Pearson’s correlation coefficient was used to
measure the strength of the correlation between vari-
ables.
RESULTS: The study evaluated 241 eyes in 182 pa-
tients with keratoconus. Both corneal surfaces showed
statistically significant decreases in average steep kera-
tometry (K2) values, corneal astigmatism, elevation at
the apex and at the thinnest point, maximum eleva-
tion in the central 4-mm area, and elevation inside the
3- and 4-mm zones and at the 3-mm ring. Regarding
anterior surface parameters, a significant decrease was
observed in flat keratometry (K1), whereas asphericity
increased. On the posterior corneal surface, no signifi-
cant changes in K1 and asphericity were observed. Poor
correlation was found between visual outcomes and
changes in tomographic parameters. The best correla-
tion was obtained for anterior corneal astigmatism.
CONCLUSIONS: ICRS implantation led to statistically
significant changes in both anterior and posterior cor-
neal surfaces. However, correlation between visual out-
comes and tomographic parameters was poor.
[J Refract Surg. 2017;33(2):110-115.]
From the Brazilian Study Group of Artificial Intelligence on Ocular Solutions,
Maceió, Brazil (JML, DL, GR, LT, PF, AM); Paulo Ferrara Eye Clinic, Belo
Horizonte, Brazil (LT, PF); Centro de Excelência em Oftalmologia, Pará de
Minas, Brazil (LT); Universidade Federal de Alagoas, Maceió, Brazil (DL, GR,
AM); and Universidade Estadual de Ciências da Saúde de Alagoas, Maceió,
Brazil (JML).
Submitted: June 6, 2016; Accepted: October 10, 2016
Dr. Ferrara has a proprietary interest in the Ferrara ring. The remaining
authors have no financial or proprietary interest in the materials presented
herein.
Correspondence: João Marcelo Lyra, MD, PhD, Rua Desembargador Tenório,
80, Maceió 57050-050, Brazil. E-mail: joaomlyra@gmail.com
doi:10.3928/1081597X-20161027-02
Tomographic Findings After Implantation of
Ferrara Intrastromal Corneal Ring Segments
in Keratoconus
João Marcelo Lyra, MD, PhD; Daniela Lyra, MD; Guilherme Ribeiro, MD; Leonardo Torquetti, PhD;
Paulo Ferrara, PhD; Aydano Machado, MD, PhD

2. 111Journal of Refractive Surgery • Vol. 33, No. 2, 2017
Tomographic Findings After Ferrara ICRS Implantation/Lyra et al
in scientific studies. Additionally, the study was ap-
proved by the local ethics committee.
All patients were intolerant to contact lenses and/
or had evidence of progression of ectasia, in addition
to a clear central cornea. The following exclusion cri-
teria were used to select patients for the study: history
of any previous eye surgery, presence of other lesions
besides keratoconus, occurrence of intraoperative or
postoperative complications, or the need for removal,
exchange, or repositioning of the ring.
All surgeries were performed under topical anes-
thesia by the same surgeon (PF) and using the manual
technique for ICRS implantation, without the use of
any suction device. The rings were implanted accord-
ing to the Ferrara Ring Nomogram, at 80% of the cor-
neal pachymetry at the incision site.6
After surgery, ke-
torolac drops were used every 15 minutes for 3 hours,
and a combination of 0.1% dexamethasone and 0.3%
moxifloxacin or ciprofloxacin drops was used every 4
hours for 7 days, as well as lubricant eye drops every 6
hours for 30 days.
Preoperative and postoperative tomography scans of
the cornea, obtained with the Pentacam, were evaluated.
Thirty-seven parameters of the two corneal surfaces were
specifically included in the current study: flat (K1) and
steep (K2) keratometry values, corneal astigmatism in the
3-mm zone (Astig), best fit sphere for the central 8-mm
zone (BFS 8mm), elevation at the apex using the 8-mm
BFS (Ele BFS 8mm Apex), elevation at the thinnest point
using the 8-mm BFS (Ele BFS 8mm Thinnest), maximum
elevation in the central 4-mm zone using the 8-mm BFS
(Ele BFS 8mm Max 4mm Zone), mean corneal thickness
measurement on a 2-, 3.2-, 4-, and 5-mm ring (Pachy),
anterior chamber depth (ACD), asphericity measurement
at 30° (Asph Q 30°), the average elevation inside 3-, 4-, 5-,
and 6-mm zones (Ele Avg Zone), and the average eleva-
tion on a 3-, 4-, 5-, and 6-mm ring (Ele Avg Ring).
The selection of these parameters was based on the
ICRS position in the cornea and the possibility of change
of any of these parameters after ICRS implantation.
The Statistical Package for the Social Sciences (ver-
sion 12.0; SPSS, Inc., Chicago, IL) was used for the sta-
tistical analysis. The results are presented as mean ±
standard deviation. For comparison of groups, the Wil-
coxon test for nonparametric samples was used. For
correlation, the Pearson’s correlation coefficient was
used. P values of less than .05 were considered statisti-
cally significant.
RESULTS
Two hundred forty-one eyes from 182 patients with
keratoconus were included in the study (113 right
eyes [46.9%]; 128 left eyes [53.1%]). One hundred five
patients were male (57.7%) and 77 (42.3%) were fe-
male. Their mean age was 28.5 ± 8.8 years (range: 16
to 60 years) and the minimum postoperative follow-
up period was 6 months (average: 29.4 months; range:
6 to 72 months). According to the Amsler–Krumeich
classification for grading the severity of keratoconus,
111 eyes (46.1%) were grade I, 95 (39.4%) were grade
II, 16 (6.6%) were grade III, and 18 eyes (7.5%) were
grade IV. A single segment was implanted in 153 eyes,
whereas a pair of segments was implanted in 88 eyes.
Visual Acuity
Corrected acuity outcomes are shown in Figures 1-2.
Tomographic Parameters
There were statistically significant postoperative de-
creases (P = .0001) in almost all anterior (Table 1) and
posterior (Table 2) surface parameters evaluated.
In both corneal surfaces, the average elevation inside
the 3- and 4-mm zones and at the 3-mm ring decreased
postoperatively (Table A, available in the online ver-
sion of this article). However, the average elevation
inside the 6-mm zone, on a 4-, 5-, and 6-mm ring, in-
Figure 1. Comparison between preoperative and postoperative Snellen
visual acuity in intrastromal corneal ring implantation. CDVA = corrected
distance visual acuity
Figure 2. Gain of lines after intrastromal corneal ring implantation. CDVA
= corrected distance visual acuity

3. 112 Copyright © SLACK Incorporated
Tomographic Findings After Ferrara ICRS Implantation/Lyra et al
creased significantly. There were no changes in the
average elevation inside a 5-mm zone. Furthermore,
a significant increase was found in average corneal
thickness (P = .0001) at the 2-mm zone (470 ± 38.58
vs 484.05 ± 41.26 µm), 3.2-mm zone (498.11 ± 35.51
vs 513.14 ± 39.08 µm), 4-mm zone (520.88 ± 35.07 vs
536.37 ± 38.74 µm), and 5-mm zone (559.44 ± 37.22 vs
573.58 ± 39.94 µm).
Relationship Between Tomographic Parameters
and Visual Outcomes
Correlation coefficients between variation in tomo-
graphic parameters and lines of vision improvement
in logMAR are described in Tables B-C (available in
the online version of this article). With regard to an-
terior surface parameters (Table B), the best statisti-
cally significant correlation was obtained for corneal
astigmatism (r = -0.2758, P = .0001). Similarly, K2 and
maximum elevation in the central 4-mm zone had poor
and inverse correlations (r = -0.2171, P = .001, and r =
-0.2092, P = .0015, respectively). The change in anterior
average elevation on a 6-mm ring correlated positively
with lines of vision (r = 0.2037, P = .0019). Addition-
ally, poor correlations were seen between visual out-
comes and changes in elevation at the thinnest point
(r = -0.1371, P = .0313), and between visual outcomes
and mean anterior elevation inside a 3-, 4-, and 6-mm
zone (r = -0.1578, P = .0136; r = -0.1261, P = .0476; and
r = 0.1371, P = .0313, respectively) and on the 5-mm
ring (r = 0.1898, P = .0035). Readings for K1, anterior
BFS for an 8-mm zone, elevation at the apex, aspheric-
ity measurement, and mean anterior elevation inside a
5-mm zone and with a 3- or 4-mm ring did not correlate
significantly with lines of vision improvement (P ≥ .05).
In regard to posterior surface parameters and ACD (Ta-
ble C), there was a weak correlation between K2, Astig,
and Ele B BFS 8mm Apex parameters and lines of vi-
sion improvement (r = 0.1722, P = .0074; r = -0.1578, P =
0.0135; and r = -0.1371, P = .344; respectively). There was
no significant correlation between changes in the other
parameters and visual outcomes (P ≥ .05).
A weak inverse correlation was obtained with
the average pachymetry reading on a 2-mm ring (r =
-0.1898, P = .0034) (Table C). Furthermore, on the 3.2-,
4-, and 5-mm ring, no significant correlation was seen
with lines of vision improvement (P ≥ .05).
TABLE 1
Preoperative and Postoperative Anterior Surface Parameters
Obtained With the Pentacam
Parameter Preoperative Mean ± SD Postoperative Mean ± SD P
K1 (D) 46.313 ± 4.119 45.117 ± 3.632 .0001
K2 (D) 50.946 ± 4.748 47.660 ± 3.825 .0001
Astig (D) 4.638 ± 2.371 2.542 ± 1.378 .0001
BFS Front 8mm 7.3200 ± 0.4217 7.5057 ± 0.4173 .0001
Ele F BFS 8mm Apex 11.12 ± 7.97 6.15 ± 6.93 .0001
Ele F BFS 8mm Thinnest 26.21 ± 12.75 12.56 ± 9.24 .0001
Ele F BSF 8mm Max 4mm Zone 32.40 ± 12.64 23.84 ± 11.89 .0001
Asph Q Front 30° -0.8067 ± 0.4677 -0.3804 ± 0.4911 .0001
F Ele Avg Zone 3mm 7.0909 ± 5.2071 3.0515 ± 3.7798 .0001
F Ele Avg Zone 4mm 3.094 ± 2.841 1.012 ± 1.707 .0001
F Ele Avg Zone 5mm -0.770 ± 2.167 -0.592 ± 1.478 .2926
F Ele Avg Zone 6mm -3.806 ± 3.230 -1.690 ± 2.558 .0001
F Ele Avg Ring 3mm 1.299 ± 2.279 -0.212 ± 1.561 .0001
F Ele Avg Ring 4mm -5.080 ± 4.420 -2.736 ± 3.790 .0001
F Ele Avg Ring 5mm -9.7672 ± 7.0155 -3.9805 ± 5.6501 .0001
F Ele Avg Ring 6mm -10.5585 ± 7.0322 -4.0535 ± 5.4399 .0001
SD = standard deviation; K1 = flat meridian curvature; D = diopters; K2 = steepest meridian curvature; Astig = corneal astigmatism in the 3-mm zone; BSF
Front 8mm = front best fit sphere for the central 8-mm zone; Ele F BFS 8mm Apex = front surface elevation at the apex using the 8-mm best fit sphere; Ele F
BFS 8mm Thinnest = front surface elevation at the thinnest point using the 8-mm best fit sphere; Ele F BSF 8mm Max 4mm Zone = front surface elevation at
the point with highest value within the 4-mm (diameter) zone centered at the apex using the 8-mm best fit sphere; Asph Q Front 30° = front surface asphericity at
30º; F Ele Avg Zone 3mm, 4mm, 5mm, and 6mm = average front elevation inside 3-, 4-, 5-, and 6-mm zones; F Ele Avg Ring 3mm, 4mm, 5mm, and 6mm =
average front elevation on a 3-, 4-, 5-, and 6-mm ring
The Pentacam is manufactured by Oculus Optikgeräte GmbH, Wetzlar, Germany.

4. 113Journal of Refractive Surgery • Vol. 33, No. 2, 2017
Tomographic Findings After Ferrara ICRS Implantation/Lyra et al
DISCUSSION
In 2003, Ferrara et al.12
analyzed anterior curvature
changes in 400 eyes with keratoconus after Ferrara ICRS
implantation. Average K readings decreased from 51.83
± 6.87 to 47.66 ± 6.08 D (P < .001). Rho et al.,1
Söglütü et
al.,2
and Salgado-Borges et al.13
found similar postopera-
tive results: 51.80 ± 4.68 to 49.59 ± 3.71 (P < .001), 50.94
± 5.01 to 47.78 ± 4.00 (P < .01), and 50.7 ± 4.2 to 47.5
± 3.7 (P = .0003) D, respectively. We found a decrease
from 48.6295 ± 4.2837 D preoperatively to 46.3882 ±
3.6654 D postoperatively (P < .0001).
ICRSs also affect the posterior corneal surface. It is
known that a local protrusion is found in both anterior
and posterior surfaces of keratoconic corneas14
and
that the optical contribution of the posterior corneal
surface is even more important in keratoconus, espe-
cially in advanced cases.15
The Scheimpflug imaging
technology was chosen because of its proven reliabil-
ity when it comes to providing repeatable measure-
ments of curvature, elevation, and asphericity for the
posterior corneal surface in normal eyes.16
Limited
data are available about the repeatability of parameters
in keratoconic/irregular corneas. However, the corneal
tomography has been considered as the gold standard
for keratoconus assessment because it evaluates the
anterior and posterior corneal surfaces.
Rho et al.1
found that both the average and maximum
posterior keratometric measurements became signifi-
cantly steep on the posterior surface after INTACS im-
plantation (-8.03 ± 1.05 to -8.42 ± 0.87 D, P < .001, and
-8.46 ± 1.06 to 8.78 ± 0.91 D, P < .012, respectively).
However, in the current study, average K and maximum
K readings decreased from -7.1768 ± 0.8105 to -7.0384 ±
0.7832 D (P < .0001) and from -7.6776 ± 0.891 to -7.3473
± 0.8421 D (P < .0001), respectively.
ICRSs also affect corneal elevation. Rho et al.1
as-
sessed anterior elevation of the cornea at the central
and thinnest points and found a reduction from 36.88
± 20.63 to 30.44 ± 12.52 (P < .010) and 36.88 ± 20.63 to
30.44 ± 12.52 (P < .010), respectively. Sögütlü et al.13
studied only the anterior maximum elevation, and
Salgado-Borges et al.5
investigated the anterior eleva-
tion of the center point and the anterior minimum el-
evation. Both studies showed a statistically significant
TABLE 2
Preoperative and Postoperative Posterior Surface Parameters and Anterior
Chamber Depth Readings Obtained With the Pentacam
Parameter Preoperative Mean ± SD Postoperative Mean ± SD P
K1 (D) -6.6759 ± 0.8051 -6.7295 ± 0.7707 .5804
K2 (D) -7.6776 ± 0.891 -7.3473 ± 0.8421 .0001
Astig (D) 1.0058 ± 0.5089 0.6145 ± 0.3874 .0001
BFS Back 8mm 6.0334 ± 0.3755 6.1214 ± 0.4009 .0001
Ele B BFS 8mm Apex 23.477 ± 18.735 20.199 ± 16.277 .0001
Ele B BFS 8mm Thinnest 55.104 ± 27.641 39.444 ± 21.501 .0001
Ele B BSF 8mm Max 4mm Zone 61.585 ± 25.654 48.535 ± 20.216 .0001
Asph Q Back 30° -0.7367 ± 0.6626 -0.7215 ± 0.6463 .2012
B Ele Avg Zone 3mm 15.0627 ± 11.5053 12.4672 ± 10.5182 .0001
B Ele Avg Zone 4mm 6.6929 ± 5.9703 5.0676 ± 5.1661 .0001
B Ele Avg Zone 5mm -1.3021 ± 4.5832 -1.5950 ± 4.1049 .1815
B Ele Avg Zone 6mm -7.5656 ± 6.9583 -6.4900 ± 6.6068 .0001
B Ele Avg Ring 3mm 2.861 ± 4.710 1.389 ± 4.216 .0001
B Ele Avg Ring 4mm -10.328 ± 10.042 -9.542 ± 9.757 .0001
B Ele Avg Ring 5mm -19.849 ± 15.276 -16.549 ± 14.742 .0001
B Ele Avg Ring 6mm -21.572 ± 14.782 -16.958 ± 13.988 .0001
AC Depth (mm) 3.4237 ± 0.3319 3.3429 ± 0.3445 .0001
SD = standard deviation; K1 = flat meridian curvature; D = diopters; K2 = steepest meridian curvature; Astig = corneal astigmatism in the 3-mm zone; BSF
Back 8mm = back best fit sphere for the central 8-mm zone; Ele B BFS 8mm Apex = back surface elevation at the apex using the 8-mm best fit sphere; Ele B
BFS 8mm Thinnest = back surface elevation at the thinnest point using the 8mm best fit sphere; Ele B BSF 8mm Max 4mm Zone = back surface elevation at
the point with highest value within the 4mm (diameter) zone centered at the apex using the 8mm best fit sphere; Asph Q Back 30± = back surface asphericity at
30º; B Ele Avg Zone 3mm, 4mm, 5mm, and 6mm = average back elevation inside 3mm, 4mm, 5mm, and 6mm zones; B Ele Avg Ring 3mm, 4mm, 5mm, and
6mm = average back elevation on a 3mm, 4mm, 5mm, and 6mm ring; AC Depth = anterior chamber depth
The Pentacam is manufactured by Oculus Optikgeräte GmbH, Wetzlar, Germany.

5. 114 Copyright © SLACK Incorporated
Tomographic Findings After Ferrara ICRS Implantation/Lyra et al
decrease in anterior elevation after ICRS implantation.
In the current study, elevation readings in the center of
the cornea and at the thinnest point were assessed, as
well as the maximum elevation inside the 4-mm cen-
tral zone. All three parameters showed a statistically
significant decrease, mostly in agreement with the pre-
vious studies.1,2
Although specific corneal parameters (eg, elevation
at the center point and thinnest point) are important
values to be analyzed, they might be less important in
patients with keratoconus because of the corneal dis-
tortion inherent to the disease. Hence, average area pa-
rameters could better describe these changes because
these would embrace keratoconus as it actually is, as
an ectatic zone. To the best of our knowledge, this is
the first study to analyze these anterior and posterior
corneal elevation parameters.
In our study, mean anterior elevation measurements
were obtained within the 3-, 4-, 5-, and 6-mm diameter
zones, and in a 3-, 4-, 5-, and 6-mm ring (Table 1). The
mean anterior elevation in a 3- and 4-mm zone showed
a statistically significant reduction. On the other hand,
the anterior elevation decreased in the 5-mm zone, al-
though it was not statistically significant, whereas it
increased in the 6-mm zone (Table 1). This difference
in variation from 3- and 4-mm zones to 5- and 6-mm
zones is explained by the fact that the ring segments
were implanted 5 mm from the corneal center. All av-
erage ring parameters (3, 4, 5, and 6 mm) showed a
statistically significant reduction (Table 1).
Regarding the posterior corneal surface elevation
parameters, Rho et al.1
found an increase in elevation
at the center point from 79.48 ± 43.15 preoperatively
to 94.60 ± 36.12 postoperatively (P < .012) and the
thinnest point from 97.40 ± 40.17 to 110.48 ± 36.56.
On the other hand, the current study revealed a de-
crease in the apex and at the thinnest point, as well as
a decrease in the maximum elevation inside the 4-mm
zone. Sögütlü et al.2
and Salgado-Borges et al.13
found
similar results.
As in the case of the anterior corneal surface, the
current study also looked into the mean posterior el-
evation inside the 3-, 4-, 5-, and 6-mm diameter zones,
as well as mean posterior elevation on a 3-, 4-, 5-, and
6-mm ring. Similar to the anterior surface parameters,
the mean elevation inside the 3- and 4-mm zones de-
creased, whereas the 5-mm zone mean elevation did
not show a statistically significant change. Unlike an-
terior elevation, mean posterior elevation in the 6-mm
zone decreased after the surgery (Table A).
Secondary to the change in corneal elevation after
ICRS implantation, BFS is also expected to change be-
cause BFS is a reference for elevation measurements.
Previous studies showed a flattening to both anterior
and posterior BFS.1,2
Our study found similar results.
Similarly, ACD changes in response to the overall cor-
neal flattening. Rho et al.1
found that ACD decreased
from 3.44 to 3.32 mm (P < .001). Our results are strik-
ingly similar to those from this earlier publication,
having shown a statistically significant reduction from
3.4237 to 3.3429 mm (P < .001).
The current study also analyzed anterior and
posterior corneal asphericity. Currently, the most
commonly accepted value in a non-keratoconic cor-
nea in the adult population is approximately -0.23
± 0.086, measured at the 8-mm optical zone.17
In
keratoconus, corneal asphericity becomes more
negative (more prolate) as the severity of the disease
increases.18
In 2010, Torquetti and Ferrara19
found
that the implantation of ICRS significantly changed
the mean corneal asphericity from -0.85 to -0.32 (P
= .000). Our study found similar results, with ante-
rior asphericity changing from -0.8067 ± 0.4677 to
-0.3804 ± 0.4911 (P < .001). Posterior asphericity did
not show any statistically significant changes after
the implantation.
After ICRS implantation, several studies1,2,20
dem-
onstrated an increase in corneal thinnest pachymetry,
but not in central pachymetry. Unlike other studies,
we chose to assess average ring measurements instead
of individual pachymetric values, due to the fact that
the ring segments create a change in areas concentric
to the corneal apex. Hence, a ring thickness reading,
rather than a point, would better explain these modi-
fications. Our study analyzed the average pachymetry
at a 3-, 4-, 5-, and 6-mm corneal ring diameter. All four
parameters showed a statistically significant increase
(Table A).
It is well established in the literature that ICRS
implantation reduces the refractive error as a result
of the so-called corneal flattening effect,21,22
usually
with an improvement in visual acuity. Earlier pub-
lications tried to find a correlation between corneal
parameter changes and visual outcomes after ICRS
implantation. Sögütlü et al.2
found a weak but sta-
tistically significant correlation between maximum
posterior corneal elevation and uncorrected distance
visual acuity, and the spherical equivalent (r = 0.18
and P = .02). The current study analyzed the corre-
lation of corneal tomographic parameter changes to
lines of vision improvement. Although several publi-
cations show that there is a significant improvement
in visual acuity after ICRS implantation, to the best
of our knowledge, no previous study tried to describe
the relationship between corneal parameter changes
and lines of vision improvement. On the anterior cor-

6. 115Journal of Refractive Surgery • Vol. 33, No. 2, 2017
Tomographic Findings After Ferrara ICRS Implantation/Lyra et al
neal surface, our study found a statistically moderate
correlation (P < .05) between lines of vision improve-
ment and anterior corneal astigmatism, anterior K2,
anterior maximum elevation in a central 4-mm zone,
and mean anterior elevation on a 6-mm ring. There
was a poor correlation with anterior elevation at the
thinnest point, anterior average elevation inside a 3-,
4-, and 6-mm zone, and on the 5-mm ring mean el-
evation (Table B). The best correlation index between
these parameters was with anterior astigmatism (r =
-0.2758, P = .0001).
Regarding the posterior surface, there was a weak
negative correlation between the K2, Astig, and Ele
B BFS 8mm Apex parameters and lines of vision im-
provement. This result shows that the more these pa-
rameters decreased, the more lines of vision the pa-
tient gained.
This study demonstrated that the implantation of
the Ferrara ICRS changes corneal tomographic param-
eters in both anterior and posterior surfaces, with an
ensuing corneal regularization. Despite the changes
in corneal parameters, there was weak correlation
between these changes and lines of vision improve-
ment. Further work is needed to better understand
this relationship.
AUTHOR CONTRIBUTIONS
Study concept and design (JML, DL, GR, LT, PF, AM); data collec-
tion (JML, DL, GR, LT, PF, AM); analysis and interpretation of data
(JML, GR, LT, PF, AM); writing the manuscript (JML, DL, GR, LT, PF,
AM); critical revision of the manuscript (JML, DL, GR, LT, PF, AM);
statistical expertise (JML, GR); administrative, technical, or material
support (JML, GR, LT, PF); supervision (JML, GR, LT, PF)
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7. TABLE A
Preoperative and Postoperative Average Pachymetry Readings
Obtained With the Pentacam for Specific Ring Diameters
Parameter Preoperative Mean ± SD Postoperative Mean ± SD P
D 2mm Pachy (µm) 470.676 ± 38.575 484.054 ± 41.261 .0001
D 3.2mm Pachy (µm) 498.112 ± 35.512 513.141 ± 39.081 .0001
D 4mm Pachy (µm) 520.876 ± 35.066 536.369 ± 38.738 .0001
D 5mm Pachy (µm) 559.440 ± 37.222 573.581 ± 39.938 .0001
SD = standard deviation; D 2mm, 3.2mm, 4mm, and 5mm Pachy = average corneal thickness measurement on a 2-, 3.2-, 4-, and 5-mm zone
The Pentacam is manufactured by Oculus Optikgeräte GmbH, Wetzlar, Germany.
TABLE B
Correlation Coefficients Between the Lines of Vision Improvement and the
Changes in Anterior Surface Parameters After ICRS Implantation
Parameter r P
K1 (D) -0.0173 .7860
K2 (D) -0.2171 .0010
Astig (D) -0.2758 .0001
BFS Front 8mm 0.0687 .2879
Ele F BFS 8mm Apex -0.1197 .0601
Ele F BFS 8mm Thinnest -0.1371 .0313
Ele F BSF 8mm Max 4mm Zone -0.2092 .0015
Asph Q Front 30° 0.0598 .6424
F Ele Avg Zone 3mm -0.1578 .0136
F Ele Avg Zone 4mm -0.1261 .0476
F Ele Avg Zone 5mm 0.0053 .9330
F Ele Avg Zone 6mm 0.1371 .0313
F Ele Avg Ring 3mm -0.0955 .1354
F Ele Avg Ring 4mm 0.1120 .0789
F Ele Avg Ring 5mm 0.1898 .0035
F Ele Avg Ring 6mm 0.2037 .0019
ICRS = intracorneal ring segment; K1 = flat meridian curvature; D = diopters; K2 = steepest meridian curvature; Astig = corneal astigmatism in the 3-mm zone;
BSF Front 8mm = front best fit sphere for the central 8-mm zone; Ele F BFS 8mm Apex = front surface elevation at the apex using the 8-mm best fit sphere; Ele
F BFS 8mm Thinnest = front surface elevation at the thinnest point using the 8-mm best fit sphere; Ele F BSF 8mm Max 4mm Zone = front surface elevation at
the point with highest value within the 4-mm (diameter) zone centered at the apex using the 8-mm best fit sphere; Asph Q Front 30° = front surface asphericity at
30°; F Ele Avg Zone 3mm , 4mm, 5mm, and 6mm = average front elevation inside 3-, 4-, 5-, and 6-mm zones; F Ele Avg Ring 3mm, 4mm, 5mm, and 6mm =
average front elevation on a 3-, 4-, 5-, and 6-mm ring
TABLE C
Correlation Coefficients Between
the Lines of Vision Improvement and
Changes in Pachymetry Measures
After ICRS Implantation
Parameter r P
D 2mm Pachy (µm) -0.1898 .0034
D 3.2mm Pachy (µm) -0.0755 .2411
D 4mm Pachy (µm) 0.0024 .9694
D 5mm Pachy (µm) 0.0706 .2741
ICRS = intracorneal ring segments; D 2mm, 3.2mm, 4mm and 5mm
Pachy = average corneal thickness measurement on a 2-, 3.2-, 4-, and
5-mm zone