effect of a closed foldable equator ring on capsular bag shrinkage in cataract surgery

J CATARACT REFRACT SURG - VOL 32, OCTOBER 2006

Effect of a closed foldable equator ring

on capsular bag shrinkage in cataract surgery

Sabine Kurz, MD, Frank Krummenauer, DSc, Carolin Dumbach, Norbert Pfeiffer, MD, H. Burkhard Dick, MD

PURPOSE: To evaluate the effect of a closed foldable equator ring (CFER) versus a conventional cap-sular tension ring (CTR) on capsular bag shrinkage.

SETTING: Department of Ophthalmology, Johannes Gutenberg-University, Mainz, Germany.

METHODS: In this prospective study, 70 eyes of 70 patients were randomized to 2 groups using a 1:1block scheme. After uneventful cataract surgery, a capsular measuring ring was implanted in all eyes tomeasure the capsular bag diameter in vivo. In Group 1, a CTR was implanted in the capsular bag. InGroup 2, a CFER was inserted. Biometric characteristics such as axial length and the horizontal and ver-tical corneal radii were measured preoperatively. The capsular bag diameter and capsulorhexis diam-eter were measured intraoperatively and 2 or 3 days as well as 1 and 3 months postoperatively.

RESULTS: There were no statistically significant or clinically relevant between-group differences in co-variants such as axial length, vertical and horizontal corneal radii, and capsulorhexis diameter. Eyeswith the CTR had slight but statistically significant capsular bag shrinkage from a median of 10.4 toa median of 10.2 mm after 3 months (P<.001). Eyes with the CFER also had slight but statistically sig-nificant capsular bag shrinkage from a median of 10.3 to a median of 10.2 mm 3 months postopera-tively (P Z .021). At baseline, the CTR group had a larger capsular bag diameter, but there were nostatistically significant differences between the groups at the 3-month follow-up (P Z .669).

CONCLUSIONS: No clinically relevant capsular bag shrinkage was observed after implantation ofa CFER or a CTR. The expected capsular bag shrinkage was the same in both groups.

J Cataract Refract Surg 2006; 32:1615–1620 Q 2006 ASCRS and ESCRS

Over the past 14 years, capsular tension rings (CTRs) have

become indispensable in cataract surgery. The rings are de-

signed to maintain the configuration and stability of the

capsule equator by improving zonular integrity and dimin-

ishing traction on the zonules.1–3 Intraoperative complica-tions such as preexisting zonular dehiscence and zonular

weakness can be managed easier with a CTR.4,5 Some

CTR designs have been developed for specific indica-

tions.6–9 Most commercially available CTRs are open and

Accepted for publication May 17, 2006.

From the Department of Ophthalmology (Kurz, Dumbach,Pfeiffer, Dick), Johannes Gutenberg-University, Mainz, and theDepartment of Clinical Epidemiology and Health Economy(Krummenauer), Technical University of Dresden, Dresden,Germany.

No author has a financial or proprietary interest in any material ormethod mentioned.

Corresponding author: Dr. Sabine Kurz, Department of Ophthal-mology, Johannes Gutenberg-University, Langenbeckstrasse 1,55101 Mainz, Germany. E-mail: [email protected].

Q 2006 ASCRS and ESCRS

Published by Elsevier Inc.

consist of single-piece, rigid poly(methyl methacrylate)

(PMMA).3,10

Shrinkage of the capsular bag, which can start im-

mediately after cataract surgery, usually stops 3 months

postoperatively.11 It can lead to intraocular lens (IOL)decentration, deformation, or tilting.12 Implanting a CTR

reduces capsular bag shrinkage.13

The goal of this randomized prospective study was to

compare the effect of a foldable closed equator ring (CFER)

and with that of an open CTR on capsular bag shrinkage.

PATIENTS AND METHODS

This study comprised 70 eyes of 70 patients having cataractsurgery by the same surgeon (H.B.D.). All patients gave written in-formed consent before surgery in accordance with the Declarationof Helsinki. The study was approved by the local ethics committeein May 2003.

Inclusion criteria were senile cataract, axial length between21.5 mm and 26.0 mm, and intact zonules and capsular bag. Pa-tients with intraoperative complications such as capsule tears orzonulysis were excluded. Other exclusion criteria were lenticularpseudoexfoliation, proliferative diabetic retinopathy, uveitis,

0886-3350/06/$-see front matterdoi:10.1016/j.jcrs.2006.05.012

1615

mailto:[email protected]

FOLDABLE EQUATOR RING AND CAPSULAR BAG SHRINKAGE

intraocular surgery, corneal diseases, ocular trauma, and pupilssmaller than 8.0 mm after medical dilation.

Preoperatively, slitlamp examination of the anterior and pos-terior segments was performed under mydriasis with tropicamideand phenylephrine hydrochloride (Neo-Synephrine). Axial lengthand anterior chamber depth were measured with the IOLMaster(Carl Zeiss).14–16

Study Design

Immediately preoperatively, the eyes were randomized into 2groups using a 1:1 block randomization scheme; the random listwas generated by an independent medical biometrician (F.K.) us-ing unit SPSS statistical software. Group 1 received a CTR, andGroup 2 received a CFER. Patients were masked to which ringthey received.

The sample size was based on the findings of a previous inde-pendent randomized trial13 that indicated an expected capsularbag shrinkage of 0.15 mm after CTR implantation and 0.38 mmafter implantation of a capsular measuring ring (CMR). This dif-ference led to the following assumptions about whether a clinicallyrelevant difference in capsular bag shrinkage inhibition betweenthe CTR and CFER supplementation could be established: Supe-riority of the CFER over the CTR would be established if theCTR led to a median shrinkage of 0.20 mm and the CFER led toa median shrinkage of 0.10 mm or less in the new trial. A samplesize of 70 eyes was derived to enable the trial to detect this differ-ence at a 5% significance level based on a statistical power of 90%.A 10% dropout rate was introduced into this setting.

To avoid bias, all postoperative measurements were done bythe same investigator (C.D.) and all intraoperative measurementsby the same surgeon.

Ring Designs

The CMR (MicroPlex KMR12, HumanOptics) is soft, thinPMMA and was designed to accurately determine capsular bagdiameter in vivo. The principle of this device has been pub-lished.11,13 The CTR (SR10, Acri.Tec) used in this study isPMMA with a 10.0 mm diameter. The CFER (Morcher) is10.2 mm in diameter and consists of 16 segments of a copolymercomprising 2-hydroxyethyl methacrylate (HEMA) and methylmethacrylate (MMA) with a water content of 28% (Figure 1).The rigid MMA segments are 0.2 mm thick and have a side tran-sition zone that is angulated to the internal direction (Figure 2).The angulation of the MMA segments provides stiffness and shapememory. The angulation also increases resistance to capsular bagshrinkage. The hydrophilic segments are approximately 0.30 mmthicker and 2.23 mm larger than the MMA segments. They narrowin the middle for flexibility. The CFER is 0.8 mm high and hasa square anterior and posterior edge.17

Surgical Technique

After uneventful phacoemulsification, bimanual irrigation/aspiration (I/A) of the lenticular cortex, and instillation of sodiumhyaluronate 1% (Healon) in the capsular bag, a CMR was im-planted in all eyes. Then, a CFER or CTR was implanted basedon the randomization. After CMR and CTR implantation, a hydro-phobic acrylic OptiEdge IOL (AR40e, AMO) was implanted. Next,the Healon was completely removed and the anterior chamber re-filled with balanced salt solution (BSS). The capsular bag size and

J CATARACT REFRACT SURG1616

the horizontal and vertical capsulorhexis diameters were deter-mined intraoperatively with a leveling rule (Engel, Geuder).

Two or 3 days postoperatively, the capsular bag size and thecapsulorhexis diameter were measured by slitlamp biomicroscopy(Haag-Streit). To confirm the slitlamp results, retroilluminationphotography was performed using a ruler to measure the distancebetween the measuring ends of the CMR and the capsulorhexis di-ameter. The measurements were repeated at 1 and 3 months.

Primary Clinical End Point

The primary clinical end point of this investigation was theintraindividual difference in capsular bag diameter (millimeters)on the day of surgery versus 3 months after implantation.

Figure 1. Scanning electron microscopy of the CFER.

Figure 2. The MMA segments (gray) of the CFER.

- VOL 32, OCTOBER 2006


Statistical Analysis

Data were recorded as medians and quartiles for continuousend points or as absolute and relative frequencies for categoricalend points. Comparisons of repeated measurements in continu-ous end points were evaluated using intraindividual differencesand ratios. Nonparametric box plots were used for demonstrationof the continuous data.

The sign test was used for significance comparisons of con-tinuous repeated measurements. The 2-sample Wilcoxon testwas used for group comparisons along continuous end points.The Fisher exact test and McNemar test for binary data were ap-plied to binary end points.

Results of these tests were summarized using P values bywhich the treatment group comparison along the primary clinicalend point was done using a 2-sample Wilcoxon test at a 5% signif-icance level. The P values derived by analysis of secondary endpoints were not adjusted for multiplicity and, therefore, indicatelocal statistical significance.

RESULTS

The mean age of the 70 patients was 76 years (inter-

quartile range 69 to 70 years). Seventy-four percent were

women. No eye was excluded because of intraoperative

complications or insufficient postoperative medical

mydriasis.

Preoperatively, the measured axial was 38% longerthan 24.0 mm in Group 1 and 22% longer than 24.0 mm

in Group 2 (P Z.194, Fisher test). There were no clinically

relevant differences between the groups in the vertical and

horizontal corneal radii. The median vertical radius was

7.77 mm (range 7.64 to 7.92 mm) in Group 1 and 7.76 mm

(range 7.56 to 7.97 mm) in Group 2. The median horizontal

radius was 7.59 mm (range 7.45 to 7.75 mm) and 7.62 mm

(range 7.46 to 7.76 mm), respectively. The median reduc-tion was 0.2 mm (interquartile range �0.1 to 0.5 mm) in

Group 1 and 0.1 mm (interquartile range �0.2 to 2.0 mm)

in Group 2. After 3 months, neither group had a statistically

significant reduction in capsulorhexis diameter (Group 1,

P Z.082; Group 2, P Z.089; both sign test). The reduction

in capsulorhexis size did not significantly differ between

groups (P Z .101, Wilcoxon test).

Eyes with the open CTR (Group 1) had slight but sta-tistically significant shrinkage of the capsular bag. Eyes

with the CFER (Group 2) had statistically significant cap-

sular bag shrinkage (Table 1 and Figure 3).

Figure 4 shows the distribution of the relative capsular

bag shrinkage between the groups in terms of the ratio be-

tween the intraoperative and postoperative assessments.

After 3 months, the median relative shrinkage was 3.4%

(range 2.0% to 4.8%) in Group 1 and 1.5% (range 0.8%to 2.0%) in Group 2. At baseline, the capsular bag diameter

was larger in Group 1 (P Z.001m Wilcoxon test); however,

there were no statistically significant differences between

J CATARACT REFRACT SURG

the groups after 1 month (P Z .281), 2 months (P Z.764), or 3 months (P Z .669).

Analysis was done to determine whether biometric fac-

tors had an influence on capsular bag shrinkage. Although

there was no clinically relevant between-group difference

in capsulorhexis diameter reduction after 3 months and

no association between the intraoperative capsulorhexis

size or change over the follow-up and capsular bag diame-

ter profiles, there was a difference between groups in thedistribution of axial lengths. Stratification of the axial

lengths showed a slight tendency toward a benefit of the

CFER over the CTR. Figure 5 shows that the capsular bag

diameter shrinkage was greater in CTR patients with an ax-

ial length longer than 24.0 mm and that the shrinkage

seemed to be less associated with the axial length in eyes

with the CFER.

DISCUSSION

The goal of this randomized prospective masked study

was to quantify the effect of a CFER and a conventional

CTR in normal eyes. Capsular bag shrinkage after ring im-

plantation was quantified with a CMR during a 3-month

follow-up. At 3 months, both the CFER and CTR prevented

capsular bag shrinkage to a similar degree. Maximum cap-

sular bag shrinkage occurred between 1 day and 1 monthpostoperatively.

Implantation of the CFER did not lead to intraopera-

tive or postoperative complications. The surgeon found im-

planting the CFER in the bag with a Sapphire cartridge

system (AMO) to be relatively easy. However, in another

clinical trial,13 visualization of the CFER or CTR was not

possible in a few cases because of inadequate pupil dilation

after cataract surgery. In these cases, minor inward bowingof the CFER cannot be ruled out. Because inadequate post-

operative pupil dilation can cause complications, we in-

cluded in our study only eyes that could be maximally

Table 1. Intraoperative and postoperative capsular bag size.

Capsular Bag Size (mm)

Group Intraop 1 Mo 2 Mo 3 Mo

CTR C CMRMean 10.4 10.2 10.2 10.1IQ range 10.3–10.7 10.1–10.5 10.0–10.4 9.9–10.4P value* d !.001 !.001 !.001

CFER C CMERMean 10.3 10.2 10.2 10.1IQ range 10.2–10.4 10.1–10.3 10.0–10.3 10.1–10.3P value* d !.001 !.001 !.021

CFER Z closed foldable equator ring; CMR Z capsule measuring ring; CTR

Z capsular tension ring; IQ Z interquartile

*Sign test; difference between 2 consecutive examinations

- VOL 32, OCTOBER 2006 1617


Figure 3. Nonparametric box plots of capsular bag

shrinkage (mm) distribution after 2 to 3 days as well

as 1 and 3 months after surgery (pre – post) (horizontal

lines indicate median and quartiles, minimum and

maximum values, which do not exceed a deviation

from the quartiles or more than 1.5 times the inter-

quartile ranges; o Z statistical outliers with deviation

from the quartiles of more than 1.5 times the inter-

quartile range; * Z statistical extreme values with de-

viation from the quartile of more than 3 times the

interquartile range).

dilated preoperatively. Even in cases of inadequate dilationresulting from the cataract surgery, the measuring exten-

sions of the CMR could be visualized at the slitlamp post-

operatively in all eyes.

Hara et al.18,19 first described a ring that was inserted in

the capsular bag equator to support the zonular apparatus

J CATARACT REFRACT SURG -1618

and to maintain the complete circular contour of the capsu-lar bag equator after cataract extraction. The closed, flexible

circular ring was silicone. It had a diameter of 10.0 mm, an

inner ring surface groove, and a square cross-section. Their

goal was to prevent capsular bag deformation and posterior

capsule opacification (PCO) after cataract extraction.

Figure 4. Nonparametric box plots of the relative

shrinkage (post/pre) of the capsular bag diameter

(horizontals Z medians and quartiles, minimum and








VOL 32, OCTOBER 2006


Figure 5. Nonparametric box plots of the relative

shrinkage (3 months after surgery/intraoperatively)

of the capsular bag diameter separated by axial length

(horizontals Z medians and quartiles, minimum and








Because the ring did not adapt to various capsule sizes, it

was never implanted in human eyes.

Nishi et al.20 report inhibition of epithelial cell migra-

tion at the capsular equator with an open, rigid bending

ring; the inhibition was the result of the ring’s square-edged

design. They found statistically reduced PCO 2 years afterIOL and capsular bending ring implantation.9 Because of

the lateral height (0.7 mm) of the capsular bending ring,

adhesion between the anterior and posterior lens capsules

can be reduced. Such adhesion can lead to lens epithelium

transformation on the back of the anterior capsule. There-

fore, anterior capsule fibrosis and shrinkage as well as PCO

can be reduced. The ring’s sharp, square-edged design can

inhibit epithelial cell migration from the periphery to thecenter of the capsular bag. However, lens epithelial cell

migration between the 2 ends of a capsular bending ring

is still possible9 because the ends do not always overlap.

In contrast, the ends of CTRs can push on each other

when capsular bag shrinkage occurs. Therefore, to our

understanding, a closed circular capsular ring with a large

lateral height and a sharp-edged design could achieve

360-degree reduction of PCO. This would keep the capsu-lar bag open, reduce anterior capsule opacification for good

visualization of the peripheral retina, and provide even ex-

tension of the capsular bag. The most commonly used

CTRs today are open and made of rigid single-piece

PMMA. Because of the characteristics of PMMA, a closed

capsular ring is almost impossible to implant safely in the

capsular bag. The composition of the CFER allows implan-

tation of a closed and foldable system.

J CATARACT REFRACT SURG

One limitation of this study is the method to determine

the capsular bag size with the CMR. Although the CMR is

very soft acrylic, one cannot predict the fraction of capsular

bag shrinkage prevented by the CMR itself. At present, the

CMR is used only for clinical research purposes and no un-

biased methods to precisely assess capsular bag diameterexist.

Furthermore, although the 2 patient groups were

strictly randomized to receive a CFER or a CTR, the eyes

with the CTR were statistically significant higher axial

length than those with the CFER. Therefore, the difference

in shrinkage from 10.4 to 10.2 mm with the CFER and 10.3

to 10.2 mm with the CTR after 3 months appears to be clin-

ically irrelevant.Another limitation of this study was the short follow-up

of 3 months. This study would be stronger if the patients had

been evaluated for 6 months or longer. However, Tehrani

et al.11 found no significant capsular bag shrinkage in nor-

mal eyes between 3 months and 6 months after CMR im-

plantation. Therefore, we selected a follow-up of 3 months.

CONCLUSION

No clinically relevant capsular bag shrinkage was ob-

served with a CFER or a CTR, and capsular bag shrinkage

was the same between the two designs. However, these con-

clusions are applicable only to the equator and tension ringsand the hydrophobic acrylic IOL used in our study. Further

examinations are necessary to evaluate the effect of the

CFER or other rings in eyes with severe capsular bag

- VOL 32, OCTOBER 2006 1619


shrinkage (eg, eyes with pseudoexfoliation). Unfortunately,

in these cases, the CMR method cannot be used because of

inadequate pupil dilation. Alternative assessment methods

should be considered to enable further investigations and

improvements to capsular rings because their ability to re-

duce capsular bag shrinkage could prevent IOL dislocationand, therefore, improve postoperative outcomes.

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VOL 32, OCTOBER 2006

effect of a closed foldable equator ring on capsular bag shrinkage in cataract surgery

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