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Influence of optic edge design, optic material, and haptic design on capsular bend configuration

Sacu, Stefan MD; Findl, Oliver MD; Menapace, Rupert MD; Buehl, Wolf MD

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Journal of Cataract & Refractive Surgery: October 2005 - Volume 31 - Issue 10 - p 1888-1894
doi: 10.1016/j.jcrs.2005.03.072
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Abstract

Posterior capsule opacification (PCO) remains the most common complication of modern cataract surgery with implantation of an intraocular lens (IOL). Over the past decade, it has become clear that optic edge design plays an important role in the prevention of PCO. The AcrySof MA60BM IOL (Alcon Laboratories), made of hydrophobic acrylic/methacrylic foldable material with sharp (“truncated”) optic edges, is associated with significantly less PCO than other IOLs.1–6 The optic material, surgical technique, and haptic design have also been described as important factors in reducing PCO.3,7–12 However, it is not fully understood why some eyes develop PCO while the posterior capsules of other eyes remain completely clear. Capsular bend formation seems to be the key to understanding how some IOLs reduce the incidence of PCO,13–15 probably by acting as a mechanical barrier against the migration of proliferating lens epithelial cells (LECs) to the posterior capsule and/or by limiting the space available for Elschnig pearl formation.16–18 In addition, Nishi19 has reported that the sharp capsular bend itself induces contact inhibition of migrating LECs.

Both the sharpness of the bend and the speed of its formation seem to be important factors in the inhibition of early postoperative LEC migration.13 Additionally, the sharp optic edge design and an overlapped continuous curvilinear capsulorhexis (CCC) induce a capsular bend, which is thought to inhibit LEC migration behind the IOL and therefore inhibit PCO.5,6,8,20 Concerning the speed of capsular bend formation in the early postoperative period, in a previous study using optical coherence tomography,15 we showed that there is a small but significant difference in capsule closure time between silicone and acrylic optic materials. However, we found no studies evaluating the relationship between the configuration of the capsular bend and the capsule opacification or capsulorhexis contraction. The type of capsular bend at the optic edge may play a role in inhibition of late LEC migration because it is typically found several months to years after surgery, usually due to a loss of barrier function at the optic rim.

The aim of this study was to develop a classification system of capsule–IOL rim configuration and evaluate the distribution of these among different IOL materials and designs and to assess the effect of capsule–optic rim configuration on PCO, anterior capsule opacification (ACO), and capsulorhexis contraction.

PATIENTS AND METHODS

Patient Recruitment and Surgical Technique

The study protocols of 659 eyes of 370 patients from 8 different prospective randomized clinical trials (6 studies with a bilateral intraindividual comparison design) were included in this study. Posterior capsule opacification data from some of these studies have been published.2,3,21,22 The study was performed at the Department of Ophthalmology at the Medical University of Vienna (Vienna General Hospital). Patients were recruited from continuous cohorts. The inclusion criterion in all studies was age-related cataract. Exclusion criteria were a history of other ocular diseases or intraocular surgery, laser treatment, diabetes requiring medical control, glaucoma, and retinal pathology that would make a postoperative visual acuity of 20/40 (decimal equivalent 0.5) or better unlikely. All the research and measurements followed the tenets of the Declaration of Helsinki.

Surgery was performed between October 1998 and July 2001 by 2 surgeons using a standardized surgical technique. A 3.5 to 3.8 mm temporal single-plane self-sealing limbocorneal incision was created. The anterior chamber was filled with an ophthalmic viscosurgical device (OVD), and a round and well-centered anterior CCC large enough to ensure complete overlap with the IOL optic was performed with a bent needle. After hydrodissection and phacoemulsification, the surgeon was unmasked to the IOL type. The IOLs were implanted in the capsular bag after folding with a forceps or with the use of an injector system. After IOL implantation, the OVD was carefully removed from the anterior chamber and the capsular bag by irrigation/aspiration (I/A). Care was taken to aspirate all OVD from the bag by slightly tilting the IOL and positioning the I/A tip behind the IOL optic. Postoperative treatment consisted of prednisolone acetate 1% (Ultracortenol) and diclofenac (Voltaren Ophtha) eyedrops 4 times a day for 1 month.

IOL Assignment

The following IOLs were evaluated: SA60AT (Alcon Surgical), SA30BL (Alcon), MA60BM (Alcon), MA30BA (Alcon), CeeOn 911A (Advanced Medical Optics), Sensar OptiEdge AR40e (Advanced Medical Optics), Sensar AR40 (Advanced Medical Optics), Clariflex (Advanced Medical Optics), SI40 (Advanced Medical Optics), Silens6 (Domilens), Microsil MS612 IOL with a round optic edge (Dr. Schmidt Intraocularlinsen GmbH), Microsil MS612 IOL with a sharp optic edge (Dr. Schmidt Intaocularlinsen GmbH), Microplex IOL with a sharp optic edge (Dr. Schmidt Intaocularlinsen GmbH), and Microplex MP260 with a round optic edge, poly(methyl methacrylate) (PMMA) IOL (Dr. Schmidt Intaocularlinsen GmbH). The differences between the IOLs are shown in Table 1.

Table 1
Table 1:
Material and design of the IOLs evaluated.

Follow-up Examinations and Image Acquisition

Follow-up examinations were performed 1 week, 1 year, and 2 or 3 years after surgery. The type of capsular bend configuration at the optic rim was examined at the slitlamp after maximum pupil dilation 1 year postoperatively. The section of the optic rim that was evaluated was between the insertions of the haptics. Typically, this section was between the 4-o'clock and 8-o'clock positions because the IOLs were typically implanted with the haptic insertions in the 3-o'clock and 9-o'clock positions. The following classification system was developed: “Y” capsular bend configuration (Y), parallel capsular bend configuration (P), right-angle capsular bend configuration (R), and wrapping capsular bend configuration (W) (Figure 1).

Figure 1.
Figure 1.:
Schematic and slitlamp images of capsular bend configurations: parallel (P), Y (Y), right-angle (R), and wrapping (W).

For assessment of fibrotic after-cataract, digital images of the anterior and posterior capsules were taken in a standardized fashion with a digital camera (Kodak NC 2000) mounted on a photo slitlamp (Zeiss 40SL-P) 1 year after surgery after maximum pupil dilation. The images were used for assessment and documentation of ACO and fibrotic PCO. The principle of this slitlamp photographic technique has been described.23 All digital images of the anterior and posterior capsules were transferred to a PC and stored on hard disc for later evaluation.

For assessment of regeneratory PCO and capsulorhexis area, standardized high-resolution digital retroillumination photographs of the posterior capsule were taken 1 week, 1 year, and 2 or 3 years after surgery. For these purposes, a digital camera (Kodak NC2000) mounted on a modified Zeiss 30 slitlamp with an external light and flashlight source was used, which provides coaxial illumination from the flash-pack through a fiber-optic cable to the camera.24 It leads to even illumination over the entire image with relatively small flash artifacts and shows high reproducibility.25

Data Evaluation and Image Analysis

The intensity of fibrotic PCO was evaluated subjectively by 2 masked examiners (score from 0 to 3, where 0 is for a clear capsule and 3, for a dense white capsule). The posterior capsule images were rearranged into a nonsystematic order to ensure that images of the same patient were not consecutive. Quantification of ACO intensity was performed objectively with Adobe Photoshop. The area of the anterior capsule in contact with the IOL was defined as the area of analysis. The dark area not directly illuminated by the slit beam within the capsulorhexis served as the control area.23 The difference in brightness between the area of analysis (from the capsulorhexis rim to the optic edge) and the control area was used to define the grade of fibrosis as a percentage (score from 0% to 100%, where 0% is a clear capsule and 100%, a dense white capsule).

The capsulorhexis area was measured using the computer program AQUA (Automated Quantification of After-Cataract, Version 2, Medical University of Vienna), which was developed at our institution in cooperation with the Technical University of Graz.26 For each patient, the 1-week and 1-year standardized digital retroillumination images (right and left eyes) were imported into the program. Thereafter, the optic diameter was measured and used as a reference to define the magnification. The capsulorhexis edge was roughly outlined with the cursor. Thereafter, the automated capsulorhexis-edge detection algorithm traces the capsulorhexis edge. Incorrect points can be corrected manually. The capsulorhexis area (mm2) was then calculated by the software.

Automated image-analysis AQUA software was also used for objective PCO evaluation. For each patient, the 2-year or 3-year digital retroillumination images were imported into the program and the region within the capsulorhexis was evaluated. The capsulorhexis edge is detected by the program in a semiautomatic (computer-aided) way. The AQUA software calculates the entropy (grade of disorder) of a bitmap. This value is converted into a score between 0 and 10 (where 0 is a clear capsule and 10, severe PCO). The system has been shown to correlate well with subjective scoring of PCO26 and is fully automated, with no subjective step in the evaluation process.

Statistical Analysis

All further evaluation was done on a personal computer using standard software (StatSoft Statistica for Windows, Release 5.1). The results were separated into groups according to the capsular bend configuration, and the mean values were calculated for the attributes mentioned above. The results in the different capsular bend configuration eyes were compared, and the differences between the groups with various capsular bend configurations were calculated after patients with missing data were removed from analysis. Data of patients who had been examined at each follow-up and whose eyes had pupil diameters larger than 6.5 mm after maximum dilation, capsulorhexes that overlapped the IOL completely, and had not had a neodymium:YAG capsulotomy were evaluated. The level of statistical significance was calculated using the repeated measures t test and the chi-square test. The P values were corrected for multiple testing, applying the method of Bonferroni-Holmes. A P value of 0.05 or less was considered significant.

RESULTS

Of the 370 patients (659 eyes) included in the study, 312 patients (522 eyes) were available for the 1-year follow-up examination. In 451 of 522 eyes (86%), capsular bend configurations could be determined and the 4 main types were observed 1 year postoperatively: P in 20 eyes (4%), Y in 97 eyes (22%), R in 234 eyes (52%), and W in 37 eyes (8%). In 63 eyes (14%), combined capsular bend configurations (Y and R or R and W) were observed. There was no significant difference between these different configurations in the amount of PCO and ACO when all IOLs were evaluated together. However, in eyes with a W configuration, the amount of capsulorhexis contraction was significantly more pronounced than in eyes with other configurations (P<.001). In eyes with a P configuration, less capsulorhexis contraction and a smaller amount of ACO were seen (P<.001).

Effect of Optic Edge Design on Capsular Bend Configuration

To assess the effect of optic edge design on capsular bend configuration, the eyes in the 3 subgroups with different optic edge designs were evaluated: sharp truncated optic edge (STOE), round anterior–sharp posterior optic edge (RASPE), and round optic edge (ROE). Table 2 shows the results in these 3 subgroups. The W configuration was found most often in silicone IOLs: the Silens6 IOL (55%), which has a rather thin round optic rim, and the Clariflex IOL (32%).

Table 2
Table 2:
Capsular bend configurations with different optic edge designs.

In the STOE subgroup, significant differences were observed between W and R configurations and between W and P configurations in capsulorhexis contraction and ACO (P<.01). In the RASPE subgroup, the only significant difference in capsulorhexis contraction was observed between W and Y types (P<.01). In the ROE subgroup, after statistical multiple test correction, the differences between the 4 capsular bend configurations did not reach the significance level (Table 2).

In addition, 4 studies with an intraindividual comparison design were evaluated; the IOLs had the same overall design and were made of the same material but had different optic edge designs (round or sharp). In these studies, the R configuration was dominant (Figure 2). In sharp optic edge IOLs, eyes with W configurations had less PCO, more ACO, and a significantly stronger capsulorhexis contraction (Table 3); in ROE IOLs, there was no significant difference between the 4 capsular bend configurations in PCO, ACO, and capsulorhexis contraction.

Figure 2.
Figure 2.:
Percentage of cases with different capsular bend configurations in intraindividual comparison studies. Sharp posterior optic edge IOLs (top) versus round posterior optic edge IOLs (fellow eyes of patients) (bottom). The 2 IOL types in each study were identical in material and design with the exception of the edge design (STOE = sharp truncated optic edge, RASPE = round anterior–sharp posterior optic edge, ROE = round optic edge).
Table 3
Table 3:
Capsular bend configurations with sharp and round posterior edge in studies with intraindividual comparison.

Effect of Optic Material and Haptic Styles on Capsular Bend Configuration

In all 3 optic materials evaluated in the study (silicone, acrylic, and PMMA), the R configuration was observed predominantly (65%, 44%, and 67%, respectively).

In STOE IOLs with 3 haptic designs (3-piece C-loop haptic, 3-piece J-loop haptic, and single-piece open-loop haptic), the R configuration was observed predominantly (48%, 57%, and 52%, respectively).

DISCUSSION

The current study assessed the influence of optic edge design, optic material, and haptic style on capsular bend configuration. Four types of capsular bend configurations of the optic rim were seen and classified. The R configuration was the most common type in all IOLs. The P type was observed in only 4% (n = 20) of all cases, especially in single-piece acrylic IOLs with an STOE. As expected, eyes with P configurations had less capsulorhexis contraction and less pronounced ACO. This outcome may be a consequence of an altered capsule wound-healing response leading to incomplete fusion and closure of the capsular bag. The P configuration was not seen in any RASPE eyes (Table 2). The Y configuration was observed most often in acrylic IOLs. In contrast to the P and the Y configurations, the W type was observed mostly in eyes with silicone optics (17% versus 8% in acrylic IOLs) and resulted in a more pronounced capsulorhexis contraction and greater intensity of ACO.

The short-term postoperative capsular bend formation has been observed and reported by Nishi and coauthors13 and Hayashi et al.14 Several laboratory studies have shown that the adhesive force to the lens capsule differs significantly among IOL materials, resulting in different effects on the behavior of LECs and/or lens fibers. A more adhesive material such as foldable acrylate may retard PCO from extending into the visual axis on the posterior capsule, possibly by acting as a mechanical barrier and/or minimizing capsule wrinkling and limiting the space between the IOL and capsule.18,27 The fact that these processes can cause different capsular bend configurations is not well known.

Some randomized clinical trials compare sharp-edged and round-edged models of IOLs otherwise identical in design and material.1,2,10,21 These studies clearly show the PCO inhibiting effect of STOE or RASPE. In our study, in the STOE and RASPE eyes, the amount of PCO (regeneratory and fibrotic) was significantly lower than in the ROE eyes. The lowest regeneratory PCO score for STOE and RASPE eyes was in eyes with a W configuration (Table 2). This is probably due to the more effective blocking of LEC migration at the posterior optic edge when the posterior capsule is taught around it, building up a high pressure at the edge and causing a sharp bend in the capsule. This situation is also referred to as the “shrink-wrap” effect. A strong capsulorhexis contraction and higher amount of ACO, which are present in W configurations, indicate the anteriorly oriented capsule traction and the shrink-wrap effect. It is possible, that this W configuration is also most resistant to later reopening of the bag due to late regeneratory PCO invading from the capsule equator. Therefore, the W configuration may be the most permanent barrier constellation of all the configurations seen.

In ROE IOLs, the W type was observed more often with the Silens6, a 3-piece silicone IOL with a rather thin optic rim. This indicates that the thickness of the optic rim may be an important factor in the development of a W configuration. In ROE IOLs, the W configuration could not prevent PCO (Table 2). This may be due to invasion of LECs at few locations along the circumference, such as the haptic–optic junctions.

Studies by Nishi and coauthors6,28,29 have led to the conclusion that the IOL material is less important than the STOE geometry of the optic rim for PCO inhibition. In a previous randomized study, we were able to show that 3 years postoperatively, the amount of PCO in silicone and acrylic STOE IOLs was comparable.3 Ursell et al.12 report it unlikely that differences in the IOL design alone are responsible for PCO inhibition and postulate that IOL material and optic surface quality play a major role in PCO formation. Several authors describe a higher incidence of PCO in PMMA and hydrogel IOLs.7,13,30,31 In this study, we found the silicone IOL group to have amounts of PCO comparable to those in the acrylic and PMMA IOL groups. However, the amount of capsulorhexis contraction and intensity of ACO were more pronounced in the silicone IOLs, regardless of optic edge and haptic design.

Concerning the influence of haptic style, in an intraindividual comparison study, the single-piece AcrySof IOL showed an insignificant tendency for more cases of P configuration compared with the multipiece AcrySof IOL (21% versus 12%, P = .08). The more bulky haptics of the single-piece AcrySof may be the reason for this capsule fusion deficit.32

In conclusion, in the present study, we developed a classification scheme for the capsular bend configurations at the optic rim. We evaluated the possible factors influencing the capsular bend formations, such as optic edge design, optic material, and haptic style. The capsular bend configuration at the optic rim is highly variable. Four capsular bend types were seen—parallel, Y shape, right angle, and wrapping. The right-angle type was the most common configuration. Eyes with a parallel configuration showed less capsulorhexis contraction and less ACO intensity. Eyes with a wrapping configuration showed more capsulorhexis contraction and more ACO. The wrapping type was observed more often with silicone IOLs.

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© 2005 by Lippincott Williams & Wilkins, Inc.