Key words
CTR - toric IOL - cataract - astigmatism - postoperative rotation
Schlüsselwörter
CTR - torische IOL - Katarakt - Astigmatismus - postoperative Rotation
Introduction
Today, cataract surgery is considered one of the types of refractive surgery. Patients
generally do not want to wear eyeglasses and/or contact lenses after the operation.
They may
have preexisting astigmatism, or cataract surgery itself may induce the condition.
Approximately 60% of cataract patients have at least 0.75 diopter (D) and 15 – 29%
have
1 – 3 D astigmatism. Before and after the operation, astigmatism can be corrected
with
spectacles, contact lenses, excimer laser, limbal relaxing incisions, opposite clear
corneal
incisions, laser arcuate incisions, and toric intraocular lens (IOL) implantation.
Toric IOL
implantation is one of the effective ways to correct astigmatism in patients with
cataracts,
which can be performed as a single procedure together with cataract surgery, with
successful
and predictable visual outcomes, stability, and without serious complications [1], [2], [3].
Effective visual outcomes after toric IOL implantation depend on the stability of
the IOL
on the targeted axis and postoperative IOL rotation. IOL axis rotations decrease visual
acuity. There will be a 3.3% cylindric power loss for every 1-degree rotation. Maximum
acceptable rotation should be less than 30 degrees [4], [5].
To prevent or minimize the IOL axis rotation, a capsular tension ring (CTR) can be
implanted together with the toric IOL, as it can provide stability and prevent rotation.
CTR
supports the capsular sac, makes it flatter, and thus has a supportive effect on IOL,
decreasing its axial rotation [6], [7], [8], [9], [10]. Although many studies have shown that CTR reduces the rotation
of the toric IOL, it has been reported that it cannot completely eliminate the postoperative
toric IOL rotation [8]. However, in all of these studies, the CTR
was implanted before the toric IOL, and only the capsular bag supporting effect of
the CTR
was utilized [7] – [10]. Therefore,
in order to achieve greater toric IOL stabilization, we started to implement the
implantation of the CTR after the toric IOL. With the implantation of the CTR after
the
toric IOL, we aimed for the CTR to overpress the toric IOL haptics and increase the
friction
between the capsular bag and the IOL haptics. Thus, we wanted to benefit from the
CTRʼs
mechanical compression on the IOL haptics and its friction force-increasing effect,
as well
as the capsular bag supportive effect. To our knowledge, this is the first study to
evaluate
the effect of CTR implantation after or before the toric IOL in terms of rotational
stability. The aim of this study was to retrospectively evaluate whether the implantation
of
the CTR after the toric IOL had an effect on the postoperative rotational stability
of the
toric IOL.
Materials and Methods
The protocol of this retrospective comparative study was approved by the local ethics
committee (KTO Karatay University, Faculty of Medicine Ethics Committee, Konya, Turkey).
A
written informed consent was obtained from all patients before the surgery. The study
was
conducted in accordance with the Helsinki Declaration.
Patients who underwent phacoemulsification combined with toric IOL implantation due
to
cataract and astigmatism between February 2018 and October 2019 and who completed
6 months
of follow-up in our clinic were enrolled in the study. Group 1 consisted of 53 eyes
of 53
patients in whom the CTR was placed into the capsular bag after the implantation of
the
toric IOL. On the other hand, group 2 consisted of 55 eyes of 55 patients in whom
the CTR
was placed into the capsular bag before the implantation of the toric IOL.
Patients who had any ocular or systemic diseases that might affect the postoperative
visual
acuity and those who had intraoperative complications such as posterior capsule rupture
and
vitreous loss were excluded from the study. All patients included in the research
had
regular astigmatism, greater than 1.5 D, measured with an auto-kerato-refractometer
(Tonoref
II, Nidek, Japan) and compared with the keratometry of the optical biometer (Nidek
AL-Scan,
Nidek Co, Gamagori, Japan) and the corneal topography (Costruzione Strumenti Oftalmici,
Florence, Italy). Tecnis toric IOL (13 mm haptic diamaters, Tecnis Toric ZCT, Johnson
&
Johnson Vision, Inc., Santa Ana, CA, USA) and 13 mm sized CTR (130AO, Hoya, Japan)
were
implanted in the eyes of all patients. The spherical power of the IOL was calculated
through
the Holladay 1 formula. A complete ocular examination was performed preoperatively,
including uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA)
with the
Snellen chart, intraocular pressure (IOP) measurement by tonometry, slit lamp biomicroscopic
examination with pupillary dilation, fundus examination, auto-refractometric, and
topographic astigmatism measurements. The cylindrical power and alignment axis of
the IOL
were calculated with an online calculator (www.tecnistoriccalc.com). The surgically induced astigmatism (SIA) value was 0.3
D.
To eliminate the cyclotorsion effect, 0 and 180 degrees and the axis for toric IOL
placement were marked in the sitting position with biomicroscopy before the surgery.
All
surgeries were performed by the same surgeon (F. U.). Before the commencement of the
surgery, a Mendez Ring was placed onto the cornea, and the axis was re-marked. Under
topical
anesthesia (proparacaine hydrochloride 0.5%), a 2.8-mm clear corneal incision on the
steep
axis was made, followed by continuous curvilinear capsulorhexis (CCC) with a diameter
of
approximately 5.5 mm and hydrodissection. The irrigation and aspiration procedures
were
performed after nucleus emulsification. In the patients of the first group, after
the toric
IOL was implanted according to the target axis, the CTR was implanted with the help
of
forceps into the capsular bag and onto the IOL haptics to provide both capsular bag
and
haptic stability ([Fig. 1]). For this procedure, the exact
position of the CTR was unimportant and its mechanical compression to the haptics
from any
location was sufficient. If the toric IOL was rotated after CTR implantation, the
toric IOL
and CTR complex could be rotated at the haptic-optic junction with the help of a Sinski
hook
and realigned to the target axis. In the second group, after the CTR was implanted
first,
the toric IOL was implanted, and subsequently, it was aligned to the target axis.
After the
viscoelastic material was aspirated completely, the accuracy of the IOL axis was checked,
and the IOL was rotated back to the alignment axis, if necessary. Finally, the entrances
were closed with stromal hydration.
Fig. 1 In a patient with iris coloboma, CTR compresses the IOL haptics from the
top and increases the friction on the haptics, enhancing rotational stability.
After the surgery, patients used a topical antibiotic (moxifloxacin 0.5%, Vigamox,
Alcon
Laboratories, Inc., Fort Worth, TX, USA) 4 × 1 daily and a topical steroid (dexamethasone
0.1%, Dexa-sine, Liba, Turkey) 6 × 1 daily, both for 1 week; in the subsequent 3 weeks,
the
steroid dosage was tapered and stopped at the end of 1 month.
Postoperatively, all the patients were examined on the 1st day, 1st week, 1st month,
and
6th month. UCVA, BCVA, IOL measurement, biomicroscopic, and fundus examinations, as
well as
autorefractive and keratometric measurements were performed. After the mydriatic
application, the IOL position was tested with a slit lamp examination to determine
the
extent of the rotation of the IOL axis. Further, the 6th month values were taken for
statistical analysis. Groups 1 and 2 were compared in terms of preoperative patient
characteristics, postoperative visual outcomes, and IOL rotation degree.
The software SPSS version 22 was used for statistical analyses. Data were compared
between
the groups by using the independent samples t-test and the chi-square test and analyzed
within the groups by using a paired t-test. A p value smaller than 0.05 was accepted
as
statistically significant.
Results
The mean age of the first group was 54.36 ± 8.68 (40 – 83) years. Further, 25 patients
were
male (47%) and 28 were female (53%). The mean age of the second group was 57.23 ± 8.08
(42 – 81) years. In this group, 27 patients were male (49%) and 28 were female (51%).
There were no significant differences between the two groups related to age and sex
(p > 0.05), the mean preoperative and postoperative spherical value, UCVA, BCVA, and
preoperative corneal astigmatism (p > 0.05). The mean postoperative spherical and
cylindrical values were significantly lower than those of the preoperative values
in both
groups (p < 0.05). The mean postoperative UCVA and BCVA were significantly better
than
those of preoperative values (p < 0.05). The mean axial length (AL) was 23.8 ± 2.3 mm
in
the first group and 23.6 ± 2.0 mm in the second group (p = 0.68).
No intraoperative complications were encountered in any of the cases in both groups.
The
preoperative and postoperative findings of both groups are presented in [Table 1]. Although the mean postoperative residual astigmatism of the
first group (− 0.29 ± 0.26) was lower than that of the second (− 0.43 ± 0.31), the
difference was not statistically significant (p = 0.16). In group 1, only 10 degrees
of
rotation was observed in 4 eyes (7.5%). However, the toric IOL rotation in group 2
was 30
degrees in 1 eye (1.8%), 20 degrees in 3 eyes (5.4%), and 10 degrees in 7 eyes (12.7%).
The
mean degree of rotation was 0.75 ± 2.66 degrees in group 1 and 2.90 ± 6.57 degrees
in group
2, which was found to be statistically significant (p = 0.02). In eyes in which the
toric
IOL was rotated, the AL was greater than 26 mm in 3 eyes (5.6%) in the first group
and in 7
eyes (12.7%) in the second group. Among these eyes with long AL in group 2, the rotation
was
30 degrees in 1 eye, 20 degrees in 3 eyes, and 10 degrees in 3 eyes.
Table 1 Preoperative and postoperative findings of
patients.
|
Parameter
|
Group 1 (CTR after toric IOL) (n = 53)
|
Group 2 (CTR before toric IOL) (n = 55)
|
P value
|
|
Abbreviations: D: diopter, logMAR: logarithm of the minimum angle of resolution,
UCVA: uncorrected visual acuity, BCVA: best-corrected visual acuity, IOL:
intraocular lens, CTR: capsular tension ring.
|
|
Age (year)
|
54.36 ± 8.68 (40 – 83)
|
57.23 ± 8.08 (42 – 81)
|
0.723
|
|
Sex (male/famale ratio)
|
25/28 (47 – 53%)
|
27/28 (49 – 51%)
|
0.816
|
|
Preoperative spherical value (D)
|
− 1.17 ± 1.22 (− 6.00 to + 4.00)
|
− 1.21 ± 1.34 (− 6.50 to + 4.25)
|
0.656
|
|
Postoperative spherical value (D)
|
− 0.16 ± 0.19 (− 0.7 to + 0.75)
|
− 0.14 ± 0.17 (− 0.75 to + 0.75)
|
0.603
|
|
Preoperative corneal astigmatism (D)
|
− 3.25 ± 1.57 (− 6.00 to − 1.75)
|
− 3.50 ± 1.66 (− 6.00 to − 1.75)
|
0.891
|
|
Postoperative residual astigmatism (D)
|
− 0.29 ± 0.26 (− 0.50 to + 0.50)
|
− 0.43 ± 0.31 (− 0.75 to + 0.75)
|
0.162
|
|
Preoperative UCVA (logMAR)
|
0.91 ± 0.24 (0.60 – 1.00)
|
0.87 ± 0.21 (0.60 – 1.00)
|
0.442
|
|
Postoperative UCVA (logMAR)
|
0.02 ± 0.05 (− 0.10 to 0.10)
|
0.03 ± 0.06 (− 0.10 to 0.10)
|
0.397
|
|
Preoperative BCVA (logMAR)
|
0.71 ± 0.36 (0.30 – 0.90)
|
0.74 ± 0.34 (0.30 – 0.90)
|
0.323
|
|
Postoperative BCVA (logMAR)
|
0.01 ± 0.06 (− 0.10 to 0.10)
|
0.02 ± 0.06 (− 0.10 to 0.10)
|
0.285
|
|
IOL rotation (degree)
|
0.75 ± 2.66 (0 – 10)
|
2.90 ± 6.57 (0 – 30)
|
0.02
|
Discussion
Astigmatism affects both visual acuity and quality and should be corrected to get
a good
vision. During cataract surgery, different techniques such as limbal relaxing incisions,
femtosecond laser-assisted corneal arcuate incisions, and toric IOL implantation can
be
applied to reduce astigmatism [2]. Of these, toric IOL
implantation is the most effective. The position of the IOL on the predetermined axis
is
very important for the maintenance of visual quality. If the IOL is rotated, the quality
and
acuity of the vision decrease [11], [12]. Asymmetrical capsular contraction, design, and material of the IOL,
capsulorhexis size, insufficient removal of viscoelastic material, Nd : YAG capsulotomy,
axial myopia, long axial length, large capsular sac, loose capsule, postoperative
itching,
and IOP increase are the factors that may affect postoperative IOL rotation [8], [9].
A 10-degree deviation will reduce the correctional effect by a third, while a 20-degree
deviation will decrease it by two-thirds. The maximum acceptable axis shift is less
than 30
degrees. If the rotation is 30 degrees or more, postoperative astigmatism increases,
and
photic phenomena may be seen. For a 1-degree rotation, the cylindrical power loss
will be
3.3% [4], [8], [13]. Bauer et al. [14] reported that the IOL rotation
after the operation was 2.5 ± 2.1 degrees. Ferreria et al. [15]
found the postoperative IOL rotation to be 3.15 ± 2.62 degrees. Grohlich et al. [16] observed that the postoperative rotation was 4.92 ± 4.10 degrees
in the Tecnis group and 4.31 ± 4.59 degrees in the Acrysof group. However, a CTR was
not
used in these studies.
CTRs are made up of polymethylmethacrylate (PMMA). They make the capsular bag unwrapped
and
flat, enhance capsular bag symmetry, and control capsular contraction. They also reduce
the
gap between the optic of the IOL and posterior capsule and inhibit the migration and
proliferation of the cells, thus improving the rotational stability of IOL [8], [9], [10].
The effect of a CTR on toric IOL rotational stability was first described by Wiley
[17]. Zhao et al. [8] compared the impact
of toric IOL implantation with and without a CTR in patients with axial myopic astigmatism
who had undergone cataract surgery. They observed that the toric IOL was situated
in the
capsular bag in all the cases, but there were more cases with IOL rotation (12 eyes)
in the
standalone group than in the combined group (4 eyes). They concluded that in patients
with
axial myopic astigmatism, a CTR can effectively increase the rotational stability
of a toric
IOL, achieving improvement in corneal astigmatism and visual acuity.
Rastogi et al. [9] compared the rotational stability of a toric
IOL implanted with a CTR to that of a toric IOL without a CTR. They observed that
the mean
degree of rotation at 3 months postoperatively was 1.85 ± 1.72 in group A and 4.02 ± 2.04
in
group B. The difference was statistically significant. They concluded that the
co-implantation of a CTR was a safe and effective technique for better rotational
stability
of toric IOLs. Miyoshi et al. [10] evaluated the effect of CTR
on surgical outcomes of toric and multifocal IOLs in eyes with zonular instability.
They
found that in toric IOLs, the co-implantation of a CTR significantly decreased decentration
and misalignment of the IOL axis, resulting in better UCVA and BCVA after surgery.
They
further concluded that a CTR decreased the tilt of multifocal IOL, achieving improvement
of
postoperative visual acuity in eyes with suspected zonular instability. Sagiv and
Sachs
[18] reported that two CTRs were required to fixate the toric
IOL in the correct position in a 74-year-old patient with cataract and high myopia.
Hahn et
al. [19] evaluated the clinical outcome in cohorts with
simultaneous implantation of a CTR and toric IOL versus without a CTR. They found
that
primary endpoint incidences for the total sample without and with CTR were 90, 92,
and 88%.
The median absolute rotations were 1.73, 1.79, and 1.72 degrees; median absolute cylinder
deviations were 0.55, 0.53; and 0.55 D; and median visual acuity was 1.0, 1.0, and
1.0,
respectively. They concluded that no clinically relevant differences among CTR subgroups
were found, and a satisfying 3-month rotational stability was achieved.
In all of the abovementioned studies that performed combined CTR implantation with
a toric
IOL, the CTR was implanted before the toric IOL. Conversely, in our technique, since
the CTR
is implanted into the capsular bag after the toric IOL, not only does the CTR stabilize
the
capsular bag, but it also compresses the IOL haptics from the top and increases the
friction
on the haptics, enhancing rotational stability. According to our results, the mean
degree of
rotation was 0.75 ± 2.66 degrees in group 1 and 2.90 ± 6.57 degrees in group 2. This
statistically significant difference between the two groups indicated that implantation
of
the CTR after the toric IOL helped achieve much more toric IOL stabilization. We used
a
13-mm haptic diameter IOL and a 13-mm closed diameter CTR for the different refractive
eyes
(− 6.5 D to + 4 D) in this study. Probably, in eyes with a short AL, CTR loops closed
in
13 mm diameters and superposed to IOL haptics. This superposition provides better
overpress
of the toric IOL haptics and increases the friction between the capsular bag and the
IOL
haptics. Thus, the IOL achieved better stabilization in these eyes as we hypothesized
and
expected at the beginning of the study. But in the longer AL eyes, CTR loops may stay
open
and have diameters greater than 13 mm. Therefore, CTR and IOL haptics are not superposed
because of the different diameters of CTR and IOL haptics. Thus, the IOL was not overpressed
by CTR and the stabilizing effect of the CTR was not adequately exploited in eyes
with a
longer AL. On the other hand, Jiang et al. [20] implanted a
four-eyelet CTR with two extra eyelets that adjusted in front of the toric IOL. They
reported that two extra eyelets can compress the IOL on the posterior capsule and
provide a
greater contact area with the toric IOL, increasing friction and reducing the risk
of
rotation. However, the main limitation of this technique is that the four-eyelet CTR
is not
widely available in all clinics. After suturing the CTR to the toric IOL haptic, Ucar
and
Ozcimen [21] placed the toric IOL-CTR complex in the capsular
bag and reported highly satisfactory postoperative visual outcomes. Although in their
study,
similar to our technique, the CTR applied top pressure to the toric IOL haptic, and
they
also took advantage of the rivet feature of the toric IOL-CTR complex. However, only
CTR
implantation without suture is a relatively easier technique than the CTR and toric
IOL
suturing technique described by Dr. Ucar [21].
Conclusion
This study had some limitations. Firstly, the study had a retrospective design, and
the
patient population was small. Secondly, a longer follow-up period is required, especially
for the follow-up of complications that may cause late rotation of the toric IOL,
such as
capsular fibrosis, PCO (posterior capsule opacification), or late zonular damage.
Another
limitation was that no digital marker system was used. Nevertheless, to avoid bias,
the
intended axis of the IOL was double-checked with both the goniometer of the slit lamp
and
the Mendez ring. Despite all these limitations, the results of our study showed that
the
implantation of a CTR after the toric IOL provides further rotational stability and
more
effective astigmatic correction. However, further multicenter studies with larger
patient
participation should be planned for long-term and definitive results.
Conclusion Box
Already known:
-
Postoperative toric IOL rotation is the main factor responsible for nonoptimal visual
outcomes after toric IOL implantation.
-
To prevent the IOL axis rotation, the CTR can be implanted before the toric IOL, as
it can provide stability and prevent rotation.
-
However, implantation of the CTR before the toric IOL cannot eliminate the toric IOL
rotation.
Newly described:
-
The implantation of the CTR after the toric IOL provides further rotational
stability. Furthermore, this method provides greater IOL stabilization than the
conventional method (CTR implantation before the toric IOL), even in eyes with a long
AL.
-
In this method, the CTR overpresses the toric IOL haptics and increases the friction
between the capsular bag and the IOL haptics, and it provides much more toric IOL
stability.
