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NR 10-12/2006
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Comparison of
surgically induced astigmatism of temporal versus superior clear
corneal incisions
Porównanie astygmatyzmu
indukowanego przez operację w przypadku otwarć od góry i skroni
w przezroczystej rogówce
Rękas Marek, Adam Klu¶, Rafał Pawlik
From the Departament of Ophthalmology, Military Health Service
Institute in Warsaw
The Head: professor Andrzej Stankiewicz, Ph.D., M.D. |
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| Summary: |
Purpose: Comparison
of the astigmatism induced by the operation based on the
2.8 mm incisions in the clear cornea, performed by
temporal approach and superior approach.
Material and methods: Retrospective analysis was
performed on the group of 65 patients (41 women and 24
men), mean age 74.5 ± 7.1 years old. We studied a series
of 70 eyes (32 right eyes and 38 left eyes). All of the
patients underwent cataract surgery by means of
ultrasonic phacoemulsification conducted at the
Department of Ophthalmology, Military Health Services
Institute in Warsaw, Poland within 2004-2005. Follow-up
examinations took place 6 months after operation. There
were DBCVA. NBCVA, intraocular pressure, anterior
segment of the eye and fundus examined. Curvature of the
cornea was measured by means of Javal’s ophthalmometry.
The results were assumed as significant in view of
corneal curvature stabilization. Vector analysis of
astigmatism was performed on the basis of method
described by Jaffe. There was preoperative astigmatism
vector (K1) and post-operative astigmatism vector (K3)
calculated, as well as surgically inducted astigmatism (SIA)
– vector (K2). From the group of 70 eyes, 19 were
excluded from the study, where vector K1 was >1.0 D as
well as four eyes, where the main opening site depended
on the size and axis of K1 vector. The group of 47 eyes
was divided according to the opening site into two
subgroups- group I (temporal approach – 2.8 mm) – 25
eyes and group II (superior approach 2.8 mm) – 22 eyes.
Statistical analysis was performed based on Statistica
package 6.0 PL., using U-Mann-Whitney’s test, Chi square
Yates’ test, Kruskal-Wailis’ variance analysis, logistic
regression and W Shapiro-Wilk’s test.
Results: Studied groups were homogeneous with
respect to age structure, sex, number of operated eyes
and pre-operative size of corneal astigmatism vector K1
(p>.05). The mean values of SIA in group I and II were
respectively: 0.63± 0.28 and 1.00 ± 0.54 and were
statistically significant (p<.05). The mean values of K3
post-operative vector measured 6 months following the
operation was: 0.54± 0.35 in the group I and 0.96 ± 0.43
in the group II. Differences between two groups show
statistical significance (p<.05). Size of SIA has
crucial influence on generating post-operative
astigmatism >1.0 D (p=.03).
Conclusions: Clear corneal temporal approach 2.8
mm is more beneficial method comparing to superior
approach of the same width, because of the scale of SIA. |
| Słowa kluczowe: |
analiza wektorowa,
astygmatyzm indukowany operacj±, otwarcie skroniowe. |
| Key words: |
vector analysis,
surgically induced astigmatism, clear corneal temporal
incision. |
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Introduction
The goal of modern cataract surgery is a quick eyesight
rehabilitation, to restore capability to work and function in
society by patient. Removal of the cataract with simultaneous
implantation of intraocular lens and limitation of iatrogenic
damage to eyeball structures during surgery enable the success
of this goal.
Flexible materials that are used in production of intraocular
lenses have revolutionized cataract surgery. Thanks to wider
usage of them, it is possible to do cataract surgery through
incision in the clear cornea, which size was diminished to 2.0
mm in coaxial phacoemulsification and to 1.0 mm with application
of bimanual technique. The successful diminishing of the main
incision led to decrease in SIA. The size of the incision is not
the only factor that has the influence on SIA, not without the
meaning remains the type and mode of the post-surgical wound
closure. At full length of the second plane of triplane opening,
magnifies as a consequence the size of healing plane and the
size of deforming forces in the cornea during healing (1, 2).
Hydration or edema of the wounds during the surgery can cause
corneal deformation (3, 4, 5) and even the very opening directly
after it is done can change the configuration of the corneal
surface in the case of thin cornea (5).
The surgical technique is a significant factor from the
iatrogenic influence on SIA. It stems from the cooperation of
the surgeon with the technical applications in particular
equipment and anatomical relations of the eye with the
surrounding structures of the orbit and eyelid. The technical
solutions of nowadays emulsifiers from one side allow for
minimal ultrasound energy exposure and from the other side they
decrease the flow of fluids through the anterior chamber via
decrease in aspiration time. The surgical technique is therefore
the optimal application of both parameters. Because the
connection between them is inversely proportional, decrease of
ultrasound energy causes simultaneous prolongation of the
aspiration time and operating time as well, and on the contrary,
increase in ultrasound energy makes the aspiration time shorter
as well as the entire operation. Consequences for the
endothelial cells in both cases could be similar. Accessibility
of the eye during cataract surgery depends on the depth of the
orbit, prominence of the upper orbital ridge and tension of the
circular muscle (1, 3, 4, 5, 6).
From the other side surgeon should avoid tension in sagittal and
transverse axis of the main incision because of the damage to
the cornea, which consequently have the influence on SIA. From
that point the main incision has the paramount importance on the
size of SIA. Amongst the many authors there is a common belief,
the opening that induced astigmatism is at least in the clear
temporal cornea (1, 4, 6). It comes from the best access to the
eye and the greatest distance from corneal apex (3, 7). Temporal
incision is not difficult for bimanual surgeons, but for
surgeons with dominant one hand it is difficult to perform on
the non-dominant side. From that point the operation is modified
by the incision from top after changing the position or from
nose without the change (3). In both cases the distance from the
corneal apex is shorter and tensions in the sagittal axis of the
opening could be greater in relation to clear corneal temporal
incision, depending on orbit anatomy (3, 6).
The goal of this paper is the comparison of SIA in patients
operated for cataract with 2.8 mm clear corneal temporal
incision and 12 o’clock incision in 6 months observation.
Materials and methods
Retrospective analysis of 70 eyes (32 right eyes and 38 left
eyes) was done in 65 patients (41 females and 24 males) in the
mean age of 74.5 ± 7.1 years. Patients underwent operations for
cataracts with ultrasound phacoemulsification method in the
Department of Ophthalmology, Military Health Service Institute
in Warsaw in the years 2004-2005.
Pre-surgical examination included best corrected distance visual
acuity – DBCVA and near best corrected visual acuity- NBCVA,
aplanation tonometry, evaluation of the anterior and posterior
segment of the eye. The power of the intraocular lens was
calculated with SRK II formula based on keratometric
measurements with Javal’s ophthalmometer and ultrasound
measurements of eye length performed with the contact method.
Phacoemulsification was performed using droplet and intra
chamber anesthesia with 0.5% Xylocaine augmented with NLA.
Triplane main incision 2.8 mm was done in clear temporal cornea
or at 12 o’clock position. Additionally in the area of clear
cornea two ancillary incisions were done.
The anterior chamber was instilled with 0.5% Xylocaine and
Adrenaline and later filled with viscoelastic (Viscoat, Provisc)
as a softshell method. Ultrasound phacoemulsification was
performed after anterior, circular capsulorhexis 5-6.0 mm,
hydrodissection and hydrodelineation were done. The cortex was
removed with irrigation and bimanual aspiration. Flexible lenses
were implanted into the lens capsule using 2.8 mm opening with
the help of applicators. After irrigation of the anterior
chamber the corneal wounds were sealed with hydratation.
Control examinations were done in day 1 after surgery and later
1, 2 and 4 weeks after surgery. DBCVA, NBCVA, intraocular
pressure, anterior chamber and fundus were evaluated each time.
During the first 4 weeks after surgery all patients received
antibiotic with steroid and NSAID into the conjunctival sac.
After 6 months from surgery control examinations were done
adding measurements of corneal parameters with Javal’s
ophthalmometer. The results were significant for stabilization
of corneal curvature after cataract surgery and included in
further analysis.
The vector analysis of astigmatism was performed with Jaffe’s
method, developed later by other authors (8, 9, 10, 11, 12).
Based on pre-surgical measurements of corneal curvature the
vector of pre-surgical astigmatism K1 was calculated. Six months
after surgery similarly the vector of post-surgical astigmatism
K3 was calculated. The vector of astigmatism inducted by surgery
K2 was the geometric sum of vectors K1 and K3 and was calculated
with the method proposed by Jaffe (10).
From the group of 70 eyes, 19 eyes, in which vector of
pre-surgical astigmatism K1 was >1.0 D were eliminated, as well
as 4 eyes in which the place of the main opening depended on the
size and vector axis K1. The group of remaining 47 eyes divided
into two groups depended on the placement of the main opening:
group I (clear temporal corneal incision-25 eyes) and group II
(12 o’clock clear corneal incision –22 eyes). Demographical data
of both groups are shown in Table I.
Statistical analysis was performed with packets Statistica 6.0
PL using tests U Mann-Whitney, Yates Chi2, ANOVA rank
Kruskal-Wallis, logistic regression and W Shapiro-Wilk.
Results
Studied groups were homogenous for age structure, sex,
number of operated eyes and pre-surgical size of the vector of
corneal astigmatism K1 (p>.05) (Table I). Mean value K1 was 0.47
± 0.23 (group I) and 0.52 ± 0.30 (group II) (Table I).
Surgically induced astigmatism-SIA-K2
The mean values SIA in group I and II were 0.63 ± 0.28 and 1.0 ±
0.54 respectively and were significantly statistically different
(p<.05) (Figure 1, Table II). In 88.0% of operated eyes in group
I SIA was smaller than 1.0 D and in 48.0% was smaller or equal
0.6 D, only in 12.0% of eyes was greater than 1.0 D. In group II
SIA <1.0 D was in 50.0% and <0.6 D in 22.7% of operated eyes and
in as high as 50.0% of operated eyes SIA was greater than 1.0 D
(Figure 2). The surgical methods used are reproducible,
distribution of vector K2 in group I and II fits within the
criteria of normal distribution (p>.05) (Figure 2). Upper
confidence interval for mean value in group I (CI 0.51-0.74) is
at the same time lower interval border for group II (CI
0.75-1.23) in 95% probability (95% CI).
Post-surgical corneal astigmatism-K3
The mean values of post-surgical astigmatism vector 6 months
after operation were 0.54 ± 0.35 in group I and 0.96 ± 0.43 in
group II. The difference between the groups shows statistical
significance (p<.05) (Figure 3, Table III). In 88.0% of the
operated eyes in group I post-surgical astigmatism was smaller
than 1.0 D, and in 76.0% of the eyes was smaller or equal to 0.6
D, and in 12.0% was greater than 1.0 D. In group II vector K3 <
1.0 D was in 59.1%, smaller or equal to 0.6 D in 27.3% and
greater than 1.0 D in 41.9% of operated eyes (Figure 4). The
influence on the size of post-surgical vector of astigmatism K3
was verified with logistic regression. SIA has decisive
influence on development of post-surgical astigmatism greater
than 1.0 D (p=.003). On the other hand the influence of the
vector K1 on post-surgical astigmatism >1.0 D is statistically
non-significant (p=.426), which was also postulated in this work
(Table I). |
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Discussion
The best advantage of the clear corneal temporal incision
for bimanual surgeons is no doubt the best access to the eye
during surgery (13). The capability of independent use of hands
allows to solve other different surgical situations in the most
efficient and uncomplicated way, therefore it should be the goal
in the training of cataract surgeons. On the other hand
elongation of the studies would lose its value if done only for
the purpose of medical art.
Amongst many authors there is a common belief that clear corneal
temporal incision is the most advantageous and the least
interfering in pre-surgical corneal curvature, and consequently
its influence on the size of SIA is the smallest without the
consideration of the size of the incision (1-6). Borasio et al.
think, that up to 2.6 D of pre-surgical astigmatism with the
incision 3.2 mm there is no difference between the clear corneal
temporal and the incision in the positive axis of astigmatism
(13). Despite the fact that SIA in the group with the incision
on axis was 0.63 D and in the group of clear corneal temporal
incision was 0.34 D and results were statistically significant,
there was no influence on end-point visual acuity in studied
groups. Therefore Borasio et al. recommend clear corneal
temporal incision with pre-surgical astigmatism of up to 2.6 D
(13). SIA in group I in our studies was calculated after 6
months from the operation and was 0.63 D. The short observation
period in Borasio’s work, which was only 7 weeks is long enough
to compare the groups, but it is difficult to accept as final
result. SIA in Cohen’s et al. studies after 6 months observation
was in the clear corneal temporal group 0.47 D but in 12 o’clock
and nose incision was 1.05 D (6). The results were based on
topographical studies of the central 3.0 mm corneal zone and
showed significant difference between the groups. The
differences statistically significant affected SIA in the zone
between 3-5.0 mm from the corneal center and were 0.5 D and 1.01
D respectively (6). Work by Kohen et al. was done after
phacoemulsification from corneo-scleral tunel 3.6 to 3.8 mm,
they confirm advantage of clear corneal incision in relation to
upper-nasal quadrant incision (6), although it is difficult to
compare our studies. The similar trend shows in the work by
Barequet et al.[1]. In the group of clear corneal temporal
incision SIA after 6 weeks was 0.85 D, but in upper-nasal
incision generated astigmatism 1.6 D. After 12 months SIA was
0.81 D and 1.29 D in groups respectively (1). It is important
observation by Barequet et al.(1) and Kohen et al.(6) that
upper-nasal incision has greater influence on astigmatism
induction with-the-rule (WTR) than clear corneal temporal
incision (1,6). In the work by Ermis et al. there was no
difference in SIA in groups with the upper-temporal incision and
upper-nasal incision in transparent cornea 3.3-3.5 mm (3). SIA
mean values after 6 months from surgery were 0.78 D and 0.77 D.
The authors state statistically significant difference between
horizontal component of SIA in the studied groups. In the
upper-nasal group it was from 0.38 ± 0.39 in the first week
after surgery to 0.24 ± 0.21D after 6 months, which, according
to authors, had the influence on fluctuation of astigmatism axis
in post-surgical time (3). In comparative studies by Lyhna et
al. SIA in the group of clear corneal temporal incision was 0.41
D with the incision size of 4.0 mm, but the corneo-scleral
incision from top and the same size generated astigmatism 0.61 D
and the results were statistically significant (4). The small
difference SIA between studied groups was the result of a shift
of the incision of the eye into the sclera 2.5 mm posteriorly
from corneal limbus (4). The incision 2.8 mm in clear cornea at
12 o’clock, that we used in our studies caused the induction of
astigmatism in the range of 1.0 D. Lyhna et al. think that
incision at 12 o’clock inducts against-the-rule (ATR)
astigmatism, which is worse tolerated by patients (4). The clear
corneal 12 o’clock incision 3.0 mm in children over 6 years old
generates astigmatism 0.75 D after 6 months from surgery, but in
children between 12-36 months old SIA was 0.00 D after 6 months
and 0.17 D after 12 months from surgery (14). Bradfield et al.
think that smaller SIA is the result of greater elasticity of
the child’s cornea, its immaturity and capability to rebuild,
that is not available in adults (14).
In refractive cataract surgery the most important element is
reproducibility, that has the impact on the shape of corneal
surface, SIA and ultimately the quality of final visual ability
of the patient after surgery (5). Our studies confirmed, that
clear corneal temporal incision as well as 12 o’clock incision
2.8 mm fulfill this criteria (Fig. 2). 12 o’clock incision is
not recommended in routine cataract surgery, but it can be
useful in small WTR astigmatisms, because of greater SIA (13,
15). The clear corneal temporal incision seems to be universal
because of its advantages and is useful in routine cataract
surgery as well as in refractive surgery of the lens.
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Praca wpłynęła do Redakcji 09.08.2006 r. (869)
Zakwalifikowano do druku 24.10.2006 r.
Adres do korespondencji (Reprint
requests to):
dr n. med. Marek Rękas
ul. Karola Szymanowskiego 63
05-260 Marki |
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