Download Changes in central corneal thickness after congenital cataract surgery

ARTICLE
Changes in central corneal thickness
after congenital cataract surgery
Amir Faramarzi, MD, Mohammad Ali Javadi, MD, Mohammad Hossein Jabbarpoor Bonyadi, MD,
Mehdi Yaseri, MS
PURPOSE: To evaluate central corneal thickness (CCT) changes after congenital cataract surgery
with or without intraocular lens (IOL) implantation.
SETTING: Ophthalmic Research Center, Labbafinejad Medical Center, Shahid Beheshti University of
Medical Sciences, Tehran, Iran.
DESIGN: Comparative case series.
METHODS: Anterior lensectomy and anterior vitrectomy were performed in eyes with congenital
cataract. Eyes had IOL implantation (pseudophakic group) or remained aphakic (aphakic group).
The CCT and intraocular pressure were measured in all cases preoperatively and 1 and 6 months
postoperatively. Age-matched normal eyes served as a control group.
RESULTS: The study evaluated 47 eyes (30 patients), 32 pseudophakic and 15 aphakic. The mean
preoperative CCT was 540 mm G 34 (SD) in the pseudophakic group, 548 G 61 mm in the aphakic
group, and 558 G 36 mm in the control group (P Z .207). The mean CCT in the aphakic group was
significantly greater than in the pseudophakic group (587 G 65 mm versus 539 G 37 mm) 1 month
postoperatively (P Z .018) and at 6 months (602 G 65 mm versus 540 G 36 mm) (P Z .012).
Although the CCT values in the pseudophakic group at 1 month and 6 months were similar to preoperative values (P Z .463 and P Z 1.00, respectively), both postoperative CCT values in the
aphakic group were significantly greater than preoperatively (P<.001).
CONCLUSIONS: The CCT in eyes with congenital cataract was similar to that in normal age-matched
eyes. However, shortly after cataract removal, the CCT was significantly greater in aphakic eyes than
in pseudophakic eyes.
Financial Disclosure: No author has a financial or proprietary interest in any material or method
mentioned.
J Cataract Refract Surg 2010; 36:2041–2047 Q 2010 ASCRS and ESCRS
Increased central corneal thickness (CCT) after removal of a congenital cataract has been reported.1–5
It is unclear whether the increased CCT is present before surgery or develops postoperatively. Most investigators believe the change occurs postoperatively.1,4
Some suggest that surgical trauma at the time of cataract extraction may compromise endothelial cell function and result in increased CCT in these patients.3,5
In adults6–9 and in children,10 a thicker central cornea is associated with higher intraocular pressure
(IOP) readings by Goldmann applanation tonometry.
The thickened cornea after congenital cataract extraction can lead to overestimation of IOP readings and
cause over diagnosis of aphakic glaucoma with overuse of antiglaucoma medications.
In this study, we sought to answer 2 questions: (1) Is
the CCT increased in eyes with congenital cataract
Q 2010 ASCRS and ESCRS
Published by Elsevier Inc.
compared with that in normal eyes? (2) Does cataract
extraction (with or without intraocular lens [IOL] implantation) have an effect on CCT? To answer these
questions, we measured the CCT in eyes with congenital cataract preoperatively and compared the results
with those in normal age-matched eyes. We continued
to measure the CCT for 6 months after cataract surgery
in aphakic eyes and pseudophakic eyes. To our knowledge, this is the first longitudinal study to analyze CCT
before and after congenital cataract extraction and to
evaluate the role of IOL implantation on CCT in pediatric cataract surgery.
PATIENTS AND METHODS
All congenital cataract cases consecutively scheduled for surgery at Labbafinejad Medical Center between January 2008
and September 2009 were enrolled in this prospective study.
0886-3350/$ - see front matter
doi:10.1016/j.jcrs.2010.07.016
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CCT CHANGES AFTER CONGENITAL CATARACT SURGERY
Normal eyes of children who had general anesthesia for urological procedures at the same center were recruited as a control group. An institutional review board reviewed and
approved the study protocol.
Inclusion criteria were congenital or developmental cataract severe enough to decrease the red reflex to less than
three tenths and significant blocking of the visual axis. Exclusion criteria were ocular pathology other than congenital cataract, including traumatic cataract, pathologic cataract,
microphthalmos, glaucoma, corneal opacity, anterior segment dysgenesis, iris coloboma, and accompanying uveitis.
All patients had a detailed preoperative evaluation. Visual
acuity was assessed using Snellen charts when possible; if
not, fixation patterns were noted. The red reflex was evaluated by direct ophthalmoscopy. Slitlamp biomicroscopy
evaluation of the anterior segment was performed preoperatively in cooperative patients. A retinal examination was performed by indirect ophthalmoscopy. If media opacity was so
severe that the retina could not be seen, B-scan ultrasonography was performed. Infants who could not cooperate for
examination were scheduled for examination under general
anesthesia. During general anesthesia, detailed ophthalmic
evaluation was done, including IOP measurement with
a Tono-Pen (Reichert). Tonometry was performed no longer
than 5 minutes after induction of anesthesia. The CCT was
measured with an ultrasonic pachymeter (Pachymeter
SP-2000, Tomey Corp.) soon after induction of anesthesia.
The pachymeter probe was placed lightly on the center of
the cornea 3 times. At each contact, the CCT was measured
10 times automatically (auto mode). The instrument
automatically calculated the mean measurement. During
the procedure, the cornea was moistened frequently with
a balanced salt solution to ensure it was adequately
hydrated. The same examiner (A.F.) performed all CCT
measurements.
Based on the findings of the examination under general
anesthesia, if cataract extraction was indicated, patients
had surgery at the same session. The IOL power was calculated using the SRK/T formula based on the keratometry
(K) reading and axial length. When keratometry could not
be performed, the standard K reading for the patient’s age
was used.11 To prevent a postoperative myopic shift, a 10%
reduction in IOL power was considered for children younger
than 5 years. A 3-piece foldable acrylic posterior chamber
IOL with poly(methyl methacrylate) haptics (AcrySof
Submitted: April 27, 2010.
Final revision submitted: July 6, 2010.
Accepted: July 10, 2010.
From the Ophthalmic Research Center (Faramarzi, Javadi, Bonyadi),
Labbafinejad Medical Center, Shahid Beheshti University of Medical
Sciences, and the Department of Epidemiology and Biostatics
(Yaseri), School of Public Health, Tehran University of Medical
Sciences, Tehran, Iran.
MA60BM, Alcon, Inc.) was implanted in pseudophakic
eyes. If the patient had bilateral cataract and was younger
than 6 months, an IOL was not implanted. In cases of unilateral cataract, an IOL was implanted in infants older than
2 months. In these cases, the nonoperated fellow eye was
considered a control for the operated eye. Bilateral cases
did not have simultaneous surgery; the second eye was
operated on no more than 1 month after the first eye.
Surgical Technique
The same experienced surgeon (A.F.) performed all procedures using general anesthesia. Preoperative pupil dilation
was achieved by tropicamide 1% eyedrops. After the necessary limbal incisions were made and the anterior chamber
was deepened with hydroxypropyl methylcellulose 2%,
a forceps-assisted anterior capsulorhexis was created. Adequate hydrodissection and manual lens aspiration with
a Simcoe irrigation/aspiration system were performed. A
posterior continuous curvilinear capsulorhexis was initiated
with a 27-gauge cystotome and completed with a capsulorhexis forceps. A 2-port central anterior vitrectomy was
performed through 2 limbal paracenteses. Machine parameters included a cut rate of 600 cuts/min and vacuum of
100 mm Hg.
If the eye was a candidate for IOL implantation, the IOL
was placed in the ciliary sulcus. Then, the optic was captured
through the posterior capsulorhexis with a second instrument (sealed-bag technique12). After meticulous irrigation
of the anterior chamber, the incisions were closed with
10-0 nylon. At the end of surgery, all eyes received a subconjunctival injection of 100 mg of cephazolin, 2 mg of
dexamethasone, and a sub-Tenon injection of 20 mg methylprednisolone acetate.
Postoperative Treatment
Postoperative treatment included betamethasone eyedrops 6 times a day, tapered over 6 weeks, and chloramphenicol eyedrops 4 times a day for 1 week. Postoperative
dilation was achieved intermittently using tropicamide 1%
to prevent synechiae formation. Patients were examined
postoperatively at 1 and 2 days, 1 and 2 weeks, and 1, 3,
and 6 months. Each visit included visual acuity, slitlamp biomicroscopy evaluation, and IOP measurement with a TonoPen when possible. One month and 6 months after surgery,
the CCT was measured. In patients unable to cooperate, the
measurement was performed using general anesthesia;
the evaluation also included a detailed ophthalmic examination including refraction, suture removal, and IOP measurement with a Tono-Pen. The method of CCT measurement
was the same as the technique used before surgery.
Statistical Analysis
Supported by the Ophthalmic Research Center, Shahid Beheshti
Medical University, Tehran, Iran.
Descriptive statistical results are presented as the mean,
standard deviation, and minimum and maximum values.
Paired t tests were used to analyze the differences between
each pair of measurements. A P value less than 0.05 was considered statistically significant.
Corresponding author: Amir Faramarzi, MD, Ophthalmic Research
Center, Labbafinejad Medical Center, Pasdaran Avenue Boostan 9
Street, Tehran 1666694516, Iran E-mail: amirfaramarzy@yahoo.
com.
RESULTS
The study enrolled 47 eyes of 30 patients; 19 patients
(63.3%) were boys. Seventeen patients had bilateral
J CATARACT REFRACT SURG - VOL 36, DECEMBER 2010
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CCT CHANGES AFTER CONGENITAL CATARACT SURGERY
Table 1. Baseline descriptive statistics by group.
Group
Variable
Pseudophakic
(n Z 32)
Aphakic
(n Z 15)
Control
(n Z 51)
37.7 G 26.9
2–102
16/16
11/10
540 G 34
5.6 G 6.1
1–28
8/7
6/3
548 G 61
29.1 G 25.6
1–96
26/25
25/1
558 G 36
P Value
!.001
Age (mo)
Mean G SD
Range
Right eye/left eye (n)
Bilateral/monolateral (n)
Mean CCT (mm) G SD
O.999
d
.207
CCT Z central corneal thickness
congenital cataract; in these cases, both eyes were entered in the study. Table 1 shows baseline characteristics
of 32 pseudophakic eyes of 21 patients, 15 aphakic eyes
of 9 patients, and 51 normal eyes of 26 patients (control
group). There was no significant difference in the mean
baseline CCT between the 3 groups (P Z .207).
Table 2 shows the preoperative and postoperative
mean CCT values in the aphakic group and pseudophakic group and the statistical analysis results in
each group and between the pseudophakic group
and the aphakic group. The difference between the 2
groups in the mean CCT at the 1-month follow-up visit
was statistically significant (P Z .018). This difference
was greater after adjustment of the 1-month CCT
values for baseline CCT values (P!.001). The difference between the 2 groups at 6 months was also statistically significant (P Z .012) (Figures 1 and 2). This
difference was greater after adjustment of the 6-month
CCT values for baseline CCT values (P!.001). After
the 2 groups were adjusted for age and preoperative
CCT values, the differences remained significant at 1
month and 6 months (P!.001) (Table 2).
In the pseudophakic group, there was no significant
difference between the 1-month and 6-month postoperative CCT values and the baseline measurements
(P Z .463 and P Z 1.00, respectively). In the aphakic
group, however, both differences were statistically
significant (P!.001) (Table 2).
Table 3 shows baseline and follow-up data comparing the 10 unilateral pseudophakic eyes and the
nonoperated fellow eyes (controls). There was no significant difference in the mean CCT measurements
between the 2 subgroups at any time.
The mean preoperative IOP was 15 G 5.6 mm Hg in
the pseudophakic group and 14.1 G 4.6 mm Hg in the
aphakic group (P Z .51). The mean IOP 6 months postoperatively was 14.5 G 4.2 mm Hg and 15.2 G 3.3 mm Hg,
respectively (P Z .39). There was no significant
Table 2. Preoperative and postoperative mean CCT values in the aphakic group and pseudophakic group and statistical analysis results in
each group and between the 2 groups.
Mean (mm) G SD
Time
Baseline
Postoperative
1 Month
CCT
Change
P value, within*
6 Months
CCT
Change
P value, within*
P Value
Pseudophakic
Group (n Z 32)
Aphakic
Group (n Z 15)
Mean Difference
(95% CI)
540 G 34
548 G 61
8 ( 36 to 19)
.831
539 G 37
2 G 17
.463
587 G 65
38 G 30
!.001
48 ( 78 to 18)
36 (21 to 52)
d
.018
!.001
d
!.001
d
d
540 G 36
0 G 18
1.0
602 G 65
50 G 31
!.001
62 ( 92 to 33)
7 (4 to 10)
d
.012
!.001
d
!.001
d
d
CI Z confidence interval; CCT Z central corneal thickness; GEE Z generalized estimating equation
*Based on paired t test
†
Adjusted for baseline values and age (based on GEE)
J CATARACT REFRACT SURG - VOL 36, DECEMBER 2010
Based on
GEE
Adjusted†
d
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CCT CHANGES AFTER CONGENITAL CATARACT SURGERY
Figure 1. Mean and 95% CI of CCT in aphakic eyes and pseudophakic eyes at baseline and postoperatively at 1 month and 6 months
(CCT Z central corneal thickness; CI Z confidence interval).
Figure 2. Mean and 95% CI of CCT changes in aphakic eyes and pseudophakic eyes at baseline and postoperatively at 1 month and
6 months (CCT Z central corneal thickness; CI Z confidence interval).
difference in the mean preoperative or 6-month postoperative IOP within the aphakic group or within the
pseudophakic group (P Z .58 and P Z .74, respectively).
There were no significant intraoperative complications. During short-term follow-up, there were 3 cases
of postoperative inflammation in the pseudophakic
group and 2 cases in the aphakic group. All cases
resolved after the frequency of the steroid eyedrops
was increased. Three cases of capsule phimosis
occurred in the pseudophakic group; in 1 case, the
visual axis was occluded and surgical membranectomy was performed 8 months after cataract surgery.
There were no cases of aphakic or pseudophakic
glaucoma during the 6-month follow-up.
Table 3. Intrasubject analysis of preoperative and postoperative mean CCT measurements in unilateral pseudophakic eyes.
Mean G SD
Time
Baseline
Postoperative
1 Month
CCT (mm)
Change (mm)
Change (%)
P value, within*
6 Months
CCT (mm)
Change (mm)
Change (%)
P value, within*
Pseudophakic
Group
(n Z 10)
Control
Group
(n Z 10)
541 G 37
540 G 38
1 ( 12 to 14)
.895
534 G 26
19 G 22
3G4
.142
545 G 22
8 G 11
1G2
.171
11 ( 33 to 11)
10 ( 7 to 27)
2 ( 1 to 5)
d
.240
.163
.164
d
544 G 40
4 G 12
1G2
.192
551 G 39
2G8
0G1
.405
7 ( 18 to 4)
6 ( 5 to 17)
1 ( 1 to 3)
d
.179
.219
.221
d
Mean Paired Difference
(95% CI)
CI Z confidence interval; CCT Z central corneal thickness
*Based on paired t test
†
Adjusted for baseline based on generalized estimating equation
J CATARACT REFRACT SURG - VOL 36, DECEMBER 2010
P Value†
CCT CHANGES AFTER CONGENITAL CATARACT SURGERY
DISCUSSION
Although there are many reports of increased CCT
after the removal of congenital cataracts,1–5 none compared the CCT values before cataract removal with the
postoperative values. Lupinacci et al.4 measured the
CCT in eyes with congenital cataracts and surgical
aphakia. They found that aphakic eyes due to congenital cataract extraction had thicker corneas than
normal phakic eyes and suggest that the increase
in CCT occurs postoperatively. They included no
pseudophakic eyes in their study.
Muir et al.1 found that the CCT was similar in eyes
with pediatric cataract and in normal control eyes
and that the CCT increased after cataract surgery.
However, in their study, the mean CCT in aphakic
eyes was greater than in the control eyes, eyes with cataract, and eyes with pseudophakia. The authors did
not mention the percentage of primary and secondary
pseudophakia.
Simsek et al.2 compared 43 eyes of 43 aphakic and
pseudophakic patients after congenital cataract surgery with eyes of 44 healthy age- and sex-matched volunteers. The mean CCT values of the aphakic eyes
were significantly greater than in the pseudophakic
eyes, in which an IOL had been implanted at the
time of congenital cataract surgery. Differences
between aphakic eyes and pseudophakic eyes in
which an IOL had been implanted secondarily were
not significant. Only 10 eyes in their study were
pseudophakic, and primary IOL implantation was
performed in 5 cases.
Simon et al.3 describe increased CCT in aphakic/
pseudophakic children compared with control
patients. In their series, only 2 primary pseudophakia
patients were included.
Nilforushan et al.5 report that the corneas in eyes
with extracted congenital cataract were significantly
thicker than in normal control eyes. They found no significant difference in the corneal endothelial cell count
or morphology between operated eyes and normal
eyes. They dismissed endothelial damage as a possible
explanation for the increase in CCT after congenital
cataract surgery. The authors propose that eyes with
congenital cataract have thicker corneas preoperatively. This differs from our findings.
All previous studies of the change in CCT after
congenital cataract surgery compared the CCT in
aphakic/pseudophakic eyes and control eyes; none
had access to preoperative CCT values. We believe
ours is the first longitudinal study of CCT changes in
patients who had congenital cataract extraction.
In the current study, the mean CCT in the normal
eyes was 558 G 36 mm, similar to values reported
by Hossein et al.13 (549 G 46 mm) and Dai et al.14
2045
(563 G 36 mm). We found that the CCT before surgery
in eyes with congenital cataract was similar to that in
normal eyes and that there was an increase in CCT
postoperatively in aphakic eyes but not in pseudophakic eyes. The mechanism of CCT increase after congenital cataract extraction remains a matter of
speculation. In normal eyes without cataract, the central cornea is thicker at birth, rapidly decreases in
thickness during the first few months of life, and
then stabilizes over time.13 This change in corneal
thickness occurring in the first months of life indicates
that corneal development continues after birth. Development of the cornea is affected by the crystalline lens
during the embryological period.15 This effect may
continue after birth, and removing the crystalline
lens at an early age may stop it. We speculate that
the crystalline lens acts as a barrier because substitution of the natural lens with an IOL in pediatric cataract surgery had no effect on CCT in our study.
Another theory of the increase in CCT after pediatric
cataract surgery is endothelial cell damage at the time
of surgery.3,5 Mechanical stress to endothelial cells
with unrecognized surgical trauma and irrigation
fluids has been proposed as a cause of endothelial
cell dysfunction and increased CCT after pediatric cataract surgery. Increased CCT was seen in aphakic eyes
but not in pseudophakic eyes in our study. Thus, it is
less probable that the increase is due to mechanical
stress during cataract surgery because theoretically,
endothelial cell trauma would be greater in pseudophakic eyes than in aphakic eyes.
There are several reports that primary pseudophakia
may be associated with a lower rate of glaucoma following surgery for congenital cataract.16–19 It has been
suggested that exposure of maturing angle structures
to the potentially harmful effect of vitreous components
is a possible factor in developing aphakic glaucoma,
and access to the trabecular meshwork is prevented
or minimized in the pseudophakic eye by the presence
of the IOL.10,16 This finding is a key component of our
theory about the barrier effect of the IOL in preventing
increased CCT after pediatric cataract surgery.
Some authors believe that surgery for congenital
cataract at an early age increases the risk for glaucoma
whether the eye is aphakic or pseudophakic.20,21 There
were no cases of postoperative glaucoma in our series.
The mean 6-month postoperative IOP was not greater
than the mean preoperative IOP in the aphakic group,
although the postoperative CCT values in those eyes
was significantly thicker than baseline measurements.
This may be because all IOP readings in our study were
performed with a Tono-Pen, and this instrument is least
affected by CCT when used to measure IOP.22,23 Goldmann applanation tonometry tends to overestimate
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CCT CHANGES AFTER CONGENITAL CATARACT SURGERY
IOP in pediatric eyes with a thick cornea,10 leading to
unnecessary prescription of antiglaucoma medications. Absence of postoperative glaucoma in our series
can be attributed to the relatively short follow-up,
primary PC IOL implantation in the majority of cases
with haptics in the ciliary sulcus instead of in the
capsular bag, and surgery at an older age (mean 37.7
months, pseudophakic group; 5.6 months, aphakic
group).
It was impossible to age match aphakic eyes with
pseudophakic eyes in our study because of the limitation of IOL implantation in very young infants;
however, we evaluated the role of age by comparing
patients of the same age in the 2 groups. After adjustment for age, the mean CCT was significantly greater
in the aphakic group than in the pseudophakic group 1
month and 6 months postoperatively (P!.001). Based
on these findings, we believe that regardless of patient
age, primary pseudophakia has a protective role
against increased CCT after pediatric cataract surgery.
Several factors control corneal hydration and therefore corneal thickness; these include evaporation, IOP,
swelling pressure, endothelial permeability, endothelial fluid pump, endothelial pump rate receptors, and
corneal epithelium.24 Our study could not clearly address the reasons for increased CCT in the eyes left
aphakic after congenital cataract surgery. Evaluation
of the corneal layers’ anatomy and function in eyes
with congenital cataract before and after cataract
extraction would help elucidate the underlying causes.
Our findings are from the first 6 months postoperatively. The results, especially in pseudophakic eyes,
may change with a longer follow-up. Another limitation is the small number of patients, especially in the
aphakic group, which makes it difficult to generalize
the results with certainty.
In conclusion, IOP measurement is the most important factor in the diagnosis of glaucoma in children.
Therefore, increased corneal thickness in aphakic
eyes after cataract extraction and its effect on IOP measurement must be kept in mind. We showed that the
CCT increases after surgery and that IOL implantation
may have a protective effect. We speculate that
vitreous factors could have an important effect on
the maturing cornea and that IOL implantation after
pediatric cataract surgery appears to protect the
cornea against these unknown factors.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
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J CATARACT REFRACT SURG - VOL 36, DECEMBER 2010
First author:
Amir Faramarzi, MD
Ophthalmic Research Center,
Labbafinejad Medical Center, Shahid
Beheshti University of Medical
Sciences, Tehran, Iran