- Email: [email protected]
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 capsular 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 1:1 block scheme. After uneventful cataract surgery, a capsular measuring ring was implanted in all eyes to measure the capsular bag diameter in vivo. In Group 1, a CTR was implanted in the capsular bag. In Group 2, a CFER was inserted. Biometric characteristics such as axial length and the horizontal and vertical corneal radii were measured preoperatively. The capsular bag diameter and capsulorhexis diameter 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 covariants such as axial length, vertical and horizontal corneal radii, and capsulorhexis diameter. Eyes with the CTR had slight but statistically significant capsular bag shrinkage from a median of 10.4 to a median of 10.2 mm after 3 months (P<.001). Eyes with the CFER also had slight but statistically significant capsular bag shrinkage from a median of 10.3 to a median of 10.2 mm 3 months postoperatively (P Z .021). At baseline, the CTR group had a larger capsular bag diameter, but there were no statistically 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 of a 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 designed to maintain the configuration and stability of the capsule equator by improving zonular integrity and diminishing traction on the zonules.1–3 Intraoperative complications 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 indications.6–9 Most commercially available CTRs are open and
consist of single-piece, rigid poly(methyl methacrylate) (PMMA).3,10 Shrinkage of the capsular bag, which can start immediately 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.
Accepted for publication May 17, 2006.
PATIENTS AND METHODS
From the Department of Ophthalmology (Kurz, Dumbach, Pfeiffer, Dick), Johannes Gutenberg-University, Mainz, and the Department of Clinical Epidemiology and Health Economy (Krummenauer), Technical University of Dresden, Dresden, Germany. No author has a financial or proprietary interest in any material or method mentioned. Corresponding author: Dr. Sabine Kurz, Department of Ophthalmology, Johannes Gutenberg-University, Langenbeckstrasse 1, 55101 Mainz, Germany. E-mail: [email protected]. Q 2006 ASCRS and ESCRS Published by Elsevier Inc.
This study comprised 70 eyes of 70 patients having cataract surgery by the same surgeon (H.B.D.). All patients gave written informed consent before surgery in accordance with the Declaration of Helsinki. The study was approved by the local ethics committee in May 2003. Inclusion criteria were senile cataract, axial length between 21.5 mm and 26.0 mm, and intact zonules and capsular bag. Patients with intraoperative complications such as capsule tears or zonulysis were excluded. Other exclusion criteria were lenticular pseudoexfoliation, proliferative diabetic retinopathy, uveitis, 0886-3350/06/$-see front matter doi:10.1016/j.jcrs.2006.05.012
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FOLDABLE EQUATOR RING AND CAPSULAR BAG SHRINKAGE
intraocular surgery, corneal diseases, ocular trauma, and pupils smaller than 8.0 mm after medical dilation. Preoperatively, slitlamp examination of the anterior and posterior segments was performed under mydriasis with tropicamide and phenylephrine hydrochloride (Neo-Synephrine). Axial length and anterior chamber depth were measured with the IOLMaster (Carl Zeiss).14–16 Study Design Immediately preoperatively, the eyes were randomized into 2 groups using a 1:1 block randomization scheme; the random list was generated by an independent medical biometrician (F.K.) using unit SPSS statistical software. Group 1 received a CTR, and Group 2 received a CFER. Patients were masked to which ring they received. The sample size was based on the findings of a previous independent randomized trial13 that indicated an expected capsular bag shrinkage of 0.15 mm after CTR implantation and 0.38 mm after implantation of a capsular measuring ring (CMR). This difference led to the following assumptions about whether a clinically relevant difference in capsular bag shrinkage inhibition between the CTR and CFER supplementation could be established: Superiority of the CFER over the CTR would be established if the CTR led to a median shrinkage of 0.20 mm and the CFER led to a median shrinkage of 0.10 mm or less in the new trial. A sample size of 70 eyes was derived to enable the trial to detect this difference 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 by the same investigator (C.D.) and all intraoperative measurements by the same surgeon.
Figure 1. Scanning electron microscopy of the CFER.
Ring Designs
Primary Clinical End Point
The CMR (MicroPlex KMR12, HumanOptics) is soft, thin PMMA and was designed to accurately determine capsular bag diameter in vivo. The principle of this device has been published.11,13 The CTR (SR10, Acri.Tec) used in this study is PMMA with a 10.0 mm diameter. The CFER (Morcher) is 10.2 mm in diameter and consists of 16 segments of a copolymer comprising 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) with a water content of 28% (Figure 1). The rigid MMA segments are 0.2 mm thick and have a side transition zone that is angulated to the internal direction (Figure 2). The angulation of the MMA segments provides stiffness and shape memory. The angulation also increases resistance to capsular bag shrinkage. The hydrophilic segments are approximately 0.30 mm thicker and 2.23 mm larger than the MMA segments. They narrow in the middle for flexibility. The CFER is 0.8 mm high and has a square anterior and posterior edge.17
The primary clinical end point of this investigation was the intraindividual difference in capsular bag diameter (millimeters) on the day of surgery versus 3 months after implantation.
the horizontal and vertical capsulorhexis diameters were determined intraoperatively with a leveling rule (Engel, Geuder). Two or 3 days postoperatively, the capsular bag size and the capsulorhexis diameter were measured by slitlamp biomicroscopy (Haag-Streit). To confirm the slitlamp results, retroillumination photography was performed using a ruler to measure the distance between the measuring ends of the CMR and the capsulorhexis diameter. The measurements were repeated at 1 and 3 months.
Surgical Technique After uneventful phacoemulsification, bimanual irrigation/ aspiration (I/A) of the lenticular cortex, and instillation of sodium hyaluronate 1% (Healon) in the capsular bag, a CMR was implanted in all eyes. Then, a CFER or CTR was implanted based on the randomization. After CMR and CTR implantation, a hydrophobic acrylic OptiEdge IOL (AR40e, AMO) was implanted. Next, the Healon was completely removed and the anterior chamber refilled with balanced salt solution (BSS). The capsular bag size and
1616
Figure 2. The MMA segments (gray) of the CFER.
J CATARACT REFRACT SURG - VOL 32, OCTOBER 2006
FOLDABLE EQUATOR RING AND CAPSULAR BAG SHRINKAGE
Statistical Analysis
Table 1. Intraoperative and postoperative capsular bag size.
Data were recorded as medians and quartiles for continuous end points or as absolute and relative frequencies for categorical end points. Comparisons of repeated measurements in continuous end points were evaluated using intraindividual differences and ratios. Nonparametric box plots were used for demonstration of the continuous data. The sign test was used for significance comparisons of continuous repeated measurements. The 2-sample Wilcoxon test was used for group comparisons along continuous end points. The Fisher exact test and McNemar test for binary data were applied to binary end points. Results of these tests were summarized using P values by which the treatment group comparison along the primary clinical end point was done using a 2-sample Wilcoxon test at a 5% significance level. The P values derived by analysis of secondary end points were not adjusted for multiplicity and, therefore, indicate local statistical significance.
RESULTS
The mean age of the 70 patients was 76 years (interquartile 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% longer than 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 reduction 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 statistically significant shrinkage of the capsular bag. Eyes with the CFER (Group 2) had statistically significant capsular 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 between 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
Capsular Bag Size (mm) Group CTR C CMR Mean IQ range P value* CFER C CMER Mean IQ range P value*
Intraop
1 Mo
2 Mo
3 Mo
10.4 10.3–10.7 d
10.2 10.1–10.5 !.001
10.2 10.0–10.4 !.001
10.1 9.9–10.4 !.001
10.3 10.2–10.4 d
10.2 10.1–10.3 !.001
10.2 10.0–10.3 !.001
10.1 10.1–10.3 !.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
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 factors 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 diameter profiles, there was a difference between groups in the distribution 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 axial 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 implantation 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 capsular bag shrinkage occurred between 1 day and 1 month postoperatively. Implantation of the CFER did not lead to intraoperative or postoperative complications. The surgeon found implanting 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 bowing of the CFER cannot be ruled out. Because inadequate postoperative pupil dilation can cause complications, we included in our study only eyes that could be maximally
J CATARACT REFRACT SURG - VOL 32, OCTOBER 2006
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FOLDABLE EQUATOR RING AND CAPSULAR BAG SHRINKAGE
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 interquartile ranges; o Z statistical outliers with deviation from the quartiles of more than 1.5 times the interquartile range; * Z statistical extreme values with deviation from the quartile of more than 3 times the interquartile range).
dilated preoperatively. Even in cases of inadequate dilation resulting from the cataract surgery, the measuring extensions of the CMR could be visualized at the slitlamp postoperatively 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
and to maintain the complete circular contour of the capsular 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 maximum values, which do not exceed a deviation from the quartiles or more than 1.5 times the interquartile ranges; o Z statistical outliers with deviation from the quartiles of more than 1.5 times the interquartile range; * Z statistical extreme values with deviation from the quartile of more than 3 times the interquartile range).
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FOLDABLE EQUATOR RING AND CAPSULAR BAG SHRINKAGE
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 maximum values, which do not exceed a deviation from the quartiles or more than 1.5 times the interquartile ranges; o Z statistical outliers with deviation from the quartiles of more than 1.5 times the interquartile range; * Z statistical extreme values with deviation from the quartile of more than 3 times the interquartile range).
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 migration 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 after IOL 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. Therefore, 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 the center 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 capsular bag open, reduce anterior capsule opacification for good visualization of the peripheral retina, and provide even extension 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 implantation of a closed and foldable system.
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 unbiased methods to precisely assess capsular bag diameter exist. 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 clinically 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 normal eyes between 3 months and 6 months after CMR implantation. Therefore, we selected a follow-up of 3 months. CONCLUSION
No clinically relevant capsular bag shrinkage was observed with a CFER or a CTR, and capsular bag shrinkage was the same between the two designs. However, these conclusions are applicable only to the equator and tension rings and 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
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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 reduce capsular bag shrinkage could prevent IOL dislocation and, therefore, improve postoperative outcomes. REFERENCES 1. Strenn K, Menapace R, Vass C. Capsular bag shrinkage after implantation of an open-loop silicone lens and a poly(methyl methacrylate) capsule tension ring. J Cataract Refract Surg 1997; 23:1543–1547 2. Nagamoto T, Eguchi G. Effect of intraocular lens design on migration of lens epithelial cells onto the posterior capsule. J Cataract Refract Surg 1997; 23:866–872 3. Gimbel HV, Sun R. Clinical applications of capsular tension rings in cataract surgery. Ophthalmic Surg Lasers 2002; 33:44–53 4. Gimbel HV, Sun R, Heston JP. Management of zonular dialysis in phacoemulsification and IOL implantation using the capsular tension ring. Ophthalmic Surg Lasers 1997; 28:273–281 5. Sun R, Gimbel HV. In vitro evaluation of the efficacy of the capsular tension ring for managing zonular dialysis in cataract surgery. Ophthalmic Surg Lasers 1998; 29:502–505 6. Menapace R, Findl O, Georgopoulos M, et al. The capsular tension ring: designs, applications, and techniques. J Cataract Refract Surg 2000; 26:898–912 7. Cionni RJ, Osher RH. Endocapsular ring approach to the subluxed cataractous lens. J Cataract Refract Surg 1995; 21:245–249 8. Cionni RJ, Osher RH. Management of profound zonular dialysis or weakness with a new endocapsular ring designed for scleral fixation. J Cataract Refract Surg 1998; 24:1299–1306
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9. Nishi O, Nishi K, Menapace R, Akura J. Capsular bending ring to prevent posterior capsule opacification: 2 year follow-up. J Cataract Refract Surg 2001; 27:1359–1365 10. Kurz S, Dick HB. Spring constants of capsular tension rings. J Cataract Refract Surg 2004; 30:1993–1997 11. Tehrani M, Dick HB, Krummenauer F, et al. Capsule measuring ring to predict capsular bag diameter and follow its course after foldable intraocular lens implantation. J Cataract Refract Surg 2003; 29: 2127–2134 12. Apple DJ, Solomon KD, Tetz MR, et al. Posterior capsule opacification. Surv Ophthalmol 1992; 37:73–116 13. Kurz S, Krummenauer F, Hacker P, et al. Capsular bag shrinkage after implantation of a capsular bending or capsular tension ring. J Cataract Refract Surg 2005; 31:1915–1920 14. Tehrani M, Krummenauer F, Blom E, Dick HB. Evaluation of the practicality of optical biometry and applanation of ultrasound in 253 eyes. J Cataract Refract Surg 2003; 29:741–746 15. Tehrani M, Krummenauer F, Kumar R, Dick HB. Comparison of biometric measurements using partial coherence interferometry and applanation ultrasound. J Cataract Refract Surg 2003; 29:747–752 16. Vogel A, Dick HB, Krummenauer F. Reproducibility of optical biometry using partial coherence interferometry; intraobserver and interobserver reliability. J Cataract Refract Surg 2001; 27:1961–1968 17. Dick HB. Closed foldable capsular rings. J Cataract Refract Surg 2005; 31:467–471 18. Hara T, Hara T, Yamada Y. ‘‘Equator ring’’ for maintenance of the completely circular contour of the capsular bag equator after cataract removal. Ophthalmic Surg 1991; 22:358–359 19. Hara T, Hara T, Sakanishi K, Yamada Y. Efficacy of equator rings in an experimental rabbit study. Arch Ophthalmol 1995; 113:1060–1065 20. Nishi O, Nishi K, Mano C, et al. The inhibition of lens epithelial cell migration by a discontinuous capsular bend created by a band-shaped circular loop or a capsule-bending ring. Ophthalmic Surg Lasers 1998; 29:119–125
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 capsular 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 1:1 block scheme. After uneventful cataract surgery, a capsular measuring ring was implanted in all eyes to measure the capsular bag diameter in vivo. In Group 1, a CTR was implanted in the capsular bag. In Group 2, a CFER was inserted. Biometric characteristics such as axial length and the horizontal and vertical corneal radii were measured preoperatively. The capsular bag diameter and capsulorhexis diameter 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 covariants such as axial length, vertical and horizontal corneal radii, and capsulorhexis diameter. Eyes with the CTR had slight but statistically significant capsular bag shrinkage from a median of 10.4 to a median of 10.2 mm after 3 months (P<.001). Eyes with the CFER also had slight but statistically significant capsular bag shrinkage from a median of 10.3 to a median of 10.2 mm 3 months postoperatively (P Z .021). At baseline, the CTR group had a larger capsular bag diameter, but there were no statistically 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 of a 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 designed to maintain the configuration and stability of the capsule equator by improving zonular integrity and diminishing traction on the zonules.1–3 Intraoperative complications 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 indications.6–9 Most commercially available CTRs are open and
consist of single-piece, rigid poly(methyl methacrylate) (PMMA).3,10 Shrinkage of the capsular bag, which can start immediately 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.
Accepted for publication May 17, 2006.
PATIENTS AND METHODS
From the Department of Ophthalmology (Kurz, Dumbach, Pfeiffer, Dick), Johannes Gutenberg-University, Mainz, and the Department of Clinical Epidemiology and Health Economy (Krummenauer), Technical University of Dresden, Dresden, Germany. No author has a financial or proprietary interest in any material or method mentioned. Corresponding author: Dr. Sabine Kurz, Department of Ophthalmology, Johannes Gutenberg-University, Langenbeckstrasse 1, 55101 Mainz, Germany. E-mail: [email protected]. Q 2006 ASCRS and ESCRS Published by Elsevier Inc.
This study comprised 70 eyes of 70 patients having cataract surgery by the same surgeon (H.B.D.). All patients gave written informed consent before surgery in accordance with the Declaration of Helsinki. The study was approved by the local ethics committee in May 2003. Inclusion criteria were senile cataract, axial length between 21.5 mm and 26.0 mm, and intact zonules and capsular bag. Patients with intraoperative complications such as capsule tears or zonulysis were excluded. Other exclusion criteria were lenticular pseudoexfoliation, proliferative diabetic retinopathy, uveitis, 0886-3350/06/$-see front matter doi:10.1016/j.jcrs.2006.05.012
1615
FOLDABLE EQUATOR RING AND CAPSULAR BAG SHRINKAGE
intraocular surgery, corneal diseases, ocular trauma, and pupils smaller than 8.0 mm after medical dilation. Preoperatively, slitlamp examination of the anterior and posterior segments was performed under mydriasis with tropicamide and phenylephrine hydrochloride (Neo-Synephrine). Axial length and anterior chamber depth were measured with the IOLMaster (Carl Zeiss).14–16 Study Design Immediately preoperatively, the eyes were randomized into 2 groups using a 1:1 block randomization scheme; the random list was generated by an independent medical biometrician (F.K.) using unit SPSS statistical software. Group 1 received a CTR, and Group 2 received a CFER. Patients were masked to which ring they received. The sample size was based on the findings of a previous independent randomized trial13 that indicated an expected capsular bag shrinkage of 0.15 mm after CTR implantation and 0.38 mm after implantation of a capsular measuring ring (CMR). This difference led to the following assumptions about whether a clinically relevant difference in capsular bag shrinkage inhibition between the CTR and CFER supplementation could be established: Superiority of the CFER over the CTR would be established if the CTR led to a median shrinkage of 0.20 mm and the CFER led to a median shrinkage of 0.10 mm or less in the new trial. A sample size of 70 eyes was derived to enable the trial to detect this difference 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 by the same investigator (C.D.) and all intraoperative measurements by the same surgeon.
Figure 1. Scanning electron microscopy of the CFER.
Ring Designs
Primary Clinical End Point
The CMR (MicroPlex KMR12, HumanOptics) is soft, thin PMMA and was designed to accurately determine capsular bag diameter in vivo. The principle of this device has been published.11,13 The CTR (SR10, Acri.Tec) used in this study is PMMA with a 10.0 mm diameter. The CFER (Morcher) is 10.2 mm in diameter and consists of 16 segments of a copolymer comprising 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) with a water content of 28% (Figure 1). The rigid MMA segments are 0.2 mm thick and have a side transition zone that is angulated to the internal direction (Figure 2). The angulation of the MMA segments provides stiffness and shape memory. The angulation also increases resistance to capsular bag shrinkage. The hydrophilic segments are approximately 0.30 mm thicker and 2.23 mm larger than the MMA segments. They narrow in the middle for flexibility. The CFER is 0.8 mm high and has a square anterior and posterior edge.17
The primary clinical end point of this investigation was the intraindividual difference in capsular bag diameter (millimeters) on the day of surgery versus 3 months after implantation.
the horizontal and vertical capsulorhexis diameters were determined intraoperatively with a leveling rule (Engel, Geuder). Two or 3 days postoperatively, the capsular bag size and the capsulorhexis diameter were measured by slitlamp biomicroscopy (Haag-Streit). To confirm the slitlamp results, retroillumination photography was performed using a ruler to measure the distance between the measuring ends of the CMR and the capsulorhexis diameter. The measurements were repeated at 1 and 3 months.
Surgical Technique After uneventful phacoemulsification, bimanual irrigation/ aspiration (I/A) of the lenticular cortex, and instillation of sodium hyaluronate 1% (Healon) in the capsular bag, a CMR was implanted in all eyes. Then, a CFER or CTR was implanted based on the randomization. After CMR and CTR implantation, a hydrophobic acrylic OptiEdge IOL (AR40e, AMO) was implanted. Next, the Healon was completely removed and the anterior chamber refilled with balanced salt solution (BSS). The capsular bag size and
1616
Figure 2. The MMA segments (gray) of the CFER.
J CATARACT REFRACT SURG - VOL 32, OCTOBER 2006
FOLDABLE EQUATOR RING AND CAPSULAR BAG SHRINKAGE
Statistical Analysis
Table 1. Intraoperative and postoperative capsular bag size.
Data were recorded as medians and quartiles for continuous end points or as absolute and relative frequencies for categorical end points. Comparisons of repeated measurements in continuous end points were evaluated using intraindividual differences and ratios. Nonparametric box plots were used for demonstration of the continuous data. The sign test was used for significance comparisons of continuous repeated measurements. The 2-sample Wilcoxon test was used for group comparisons along continuous end points. The Fisher exact test and McNemar test for binary data were applied to binary end points. Results of these tests were summarized using P values by which the treatment group comparison along the primary clinical end point was done using a 2-sample Wilcoxon test at a 5% significance level. The P values derived by analysis of secondary end points were not adjusted for multiplicity and, therefore, indicate local statistical significance.
RESULTS
The mean age of the 70 patients was 76 years (interquartile 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% longer than 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 reduction 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 statistically significant shrinkage of the capsular bag. Eyes with the CFER (Group 2) had statistically significant capsular 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 between 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
Capsular Bag Size (mm) Group CTR C CMR Mean IQ range P value* CFER C CMER Mean IQ range P value*
Intraop
1 Mo
2 Mo
3 Mo
10.4 10.3–10.7 d
10.2 10.1–10.5 !.001
10.2 10.0–10.4 !.001
10.1 9.9–10.4 !.001
10.3 10.2–10.4 d
10.2 10.1–10.3 !.001
10.2 10.0–10.3 !.001
10.1 10.1–10.3 !.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
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 factors 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 diameter profiles, there was a difference between groups in the distribution 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 axial 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 implantation 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 capsular bag shrinkage occurred between 1 day and 1 month postoperatively. Implantation of the CFER did not lead to intraoperative or postoperative complications. The surgeon found implanting 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 bowing of the CFER cannot be ruled out. Because inadequate postoperative pupil dilation can cause complications, we included in our study only eyes that could be maximally
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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 interquartile ranges; o Z statistical outliers with deviation from the quartiles of more than 1.5 times the interquartile range; * Z statistical extreme values with deviation from the quartile of more than 3 times the interquartile range).
dilated preoperatively. Even in cases of inadequate dilation resulting from the cataract surgery, the measuring extensions of the CMR could be visualized at the slitlamp postoperatively 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
and to maintain the complete circular contour of the capsular 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 maximum values, which do not exceed a deviation from the quartiles or more than 1.5 times the interquartile ranges; o Z statistical outliers with deviation from the quartiles of more than 1.5 times the interquartile range; * Z statistical extreme values with deviation from the quartile of more than 3 times the interquartile range).
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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 maximum values, which do not exceed a deviation from the quartiles or more than 1.5 times the interquartile ranges; o Z statistical outliers with deviation from the quartiles of more than 1.5 times the interquartile range; * Z statistical extreme values with deviation from the quartile of more than 3 times the interquartile range).
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 migration 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 after IOL 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. Therefore, 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 the center 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 capsular bag open, reduce anterior capsule opacification for good visualization of the peripheral retina, and provide even extension 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 implantation of a closed and foldable system.
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 unbiased methods to precisely assess capsular bag diameter exist. 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 clinically 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 normal eyes between 3 months and 6 months after CMR implantation. Therefore, we selected a follow-up of 3 months. CONCLUSION
No clinically relevant capsular bag shrinkage was observed with a CFER or a CTR, and capsular bag shrinkage was the same between the two designs. However, these conclusions are applicable only to the equator and tension rings and 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
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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 reduce capsular bag shrinkage could prevent IOL dislocation and, therefore, improve postoperative outcomes. REFERENCES 1. Strenn K, Menapace R, Vass C. Capsular bag shrinkage after implantation of an open-loop silicone lens and a poly(methyl methacrylate) capsule tension ring. J Cataract Refract Surg 1997; 23:1543–1547 2. Nagamoto T, Eguchi G. Effect of intraocular lens design on migration of lens epithelial cells onto the posterior capsule. J Cataract Refract Surg 1997; 23:866–872 3. Gimbel HV, Sun R. Clinical applications of capsular tension rings in cataract surgery. Ophthalmic Surg Lasers 2002; 33:44–53 4. Gimbel HV, Sun R, Heston JP. Management of zonular dialysis in phacoemulsification and IOL implantation using the capsular tension ring. Ophthalmic Surg Lasers 1997; 28:273–281 5. Sun R, Gimbel HV. In vitro evaluation of the efficacy of the capsular tension ring for managing zonular dialysis in cataract surgery. Ophthalmic Surg Lasers 1998; 29:502–505 6. Menapace R, Findl O, Georgopoulos M, et al. The capsular tension ring: designs, applications, and techniques. J Cataract Refract Surg 2000; 26:898–912 7. Cionni RJ, Osher RH. Endocapsular ring approach to the subluxed cataractous lens. J Cataract Refract Surg 1995; 21:245–249 8. Cionni RJ, Osher RH. Management of profound zonular dialysis or weakness with a new endocapsular ring designed for scleral fixation. J Cataract Refract Surg 1998; 24:1299–1306
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9. Nishi O, Nishi K, Menapace R, Akura J. Capsular bending ring to prevent posterior capsule opacification: 2 year follow-up. J Cataract Refract Surg 2001; 27:1359–1365 10. Kurz S, Dick HB. Spring constants of capsular tension rings. J Cataract Refract Surg 2004; 30:1993–1997 11. Tehrani M, Dick HB, Krummenauer F, et al. Capsule measuring ring to predict capsular bag diameter and follow its course after foldable intraocular lens implantation. J Cataract Refract Surg 2003; 29: 2127–2134 12. Apple DJ, Solomon KD, Tetz MR, et al. Posterior capsule opacification. Surv Ophthalmol 1992; 37:73–116 13. Kurz S, Krummenauer F, Hacker P, et al. Capsular bag shrinkage after implantation of a capsular bending or capsular tension ring. J Cataract Refract Surg 2005; 31:1915–1920 14. Tehrani M, Krummenauer F, Blom E, Dick HB. Evaluation of the practicality of optical biometry and applanation of ultrasound in 253 eyes. J Cataract Refract Surg 2003; 29:741–746 15. Tehrani M, Krummenauer F, Kumar R, Dick HB. Comparison of biometric measurements using partial coherence interferometry and applanation ultrasound. J Cataract Refract Surg 2003; 29:747–752 16. Vogel A, Dick HB, Krummenauer F. Reproducibility of optical biometry using partial coherence interferometry; intraobserver and interobserver reliability. J Cataract Refract Surg 2001; 27:1961–1968 17. Dick HB. Closed foldable capsular rings. J Cataract Refract Surg 2005; 31:467–471 18. Hara T, Hara T, Yamada Y. ‘‘Equator ring’’ for maintenance of the completely circular contour of the capsular bag equator after cataract removal. Ophthalmic Surg 1991; 22:358–359 19. Hara T, Hara T, Sakanishi K, Yamada Y. Efficacy of equator rings in an experimental rabbit study. Arch Ophthalmol 1995; 113:1060–1065 20. Nishi O, Nishi K, Mano C, et al. The inhibition of lens epithelial cell migration by a discontinuous capsular bend created by a band-shaped circular loop or a capsule-bending ring. Ophthalmic Surg Lasers 1998; 29:119–125
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