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Posterior capsule opacification and neodymium:YAG laser capsulotomy rates with 2 microincision intraocular lenses: Four-year results

Schriefl, Sabine M. MD; Menapace, Rupert MD*; Stifter, Eva MD; Zaruba, Daniela MD; Leydolt, Christina MD

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Journal of Cataract & Refractive Surgery: May 2015 - Volume 41 - Issue 5 - p 956-963
doi: 10.1016/j.jcrs.2014.09.037
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Abstract

Posterior capsule opacification (PCO) is considered the most common reason for reduced visual acuity after uneventful cataract surgery in otherwise healthy eyes. The treatment is a neodymium:YAG (Nd:YAG) laser capsulotomy. Overall, the procedure is extremely safe; however, it can lead to complications such as intraocular pressure rise, ocular inflammation, or macular edema. Furthermore, Nd:YAG capsulotomy is not always easily accessible in developing countries.

Modifications in ultrasound phacoemulsification techniques have enabled surgeons to remove cataracts through incisions smaller than 2.0 mm with the microincision cataract surgery (MICS) technique.1 This allows faster healing and recovery time and reduces postoperative astigmatism; therefore, specific intraocular lenses (IOLs) that fit through incisions of 2.0 mm or smaller were developed. There is, however, evidence that these MICS IOLs lead to a higher PCO incidence than conventional IOLs.2–4

The aim of this study was to compare long-term PCO development and Nd:YAG rates between 2 microincision IOLs; that is, a 3-piece hydrophobic acrylic MICS IOL (Y-60H, Hoya Surgical Optics) and a 1-piece hydrophilic acrylic MICS IOL (MI60, Bausch & Lomb).

Patients and methods

Patients with bilateral age-related cataract were recruited in this prospective randomized clinical trial for intraindividual comparison. The study was performed at the Department of Ophthalmology, Vienna General Hospital, Medical University of Vienna, Austria. The study was approved by the Ethics Committee, Medical University of Vienna (931/2010) and registered with the United States National Institutes of Health Clinical Trials.A Patients were recruited in a continuous cohort. Informed consent for participation in research and treatment was obtained. All the research and measurements followed the tenets of the Declaration of Helsinki, and informed consent was obtained from all patients.

The inclusion criterion was bilateral age-related cataract. Exclusion criteria were previous intraocular surgery or ocular trauma, glaucoma, corneal disease, diabetic retinopathy, and any other severe retinal pathology that would make a postoperative corrected distance visual acuity (CDVA) of 20/40 (decimal equivalent 0.5) or better unlikely.

All surgery was performed between March 2008 and January 2009. Each patient received a Y-60H IOL in 1 eye (hydrophobic group) and an MI60 IOL (hydrophilic group) in the contralateral eye to allow intraindividual comparison. Both eyes were operated on in a single session (immediate sequential bilateral cataract surgery). The IOL type for the first eye was assigned by simple randomization before patient recruitment. The Y-60H is a blue light–filtering hydrophobic acrylic 3-piece IOL with poly(methyl methacrylate) (PMMA) C-loop haptics. The MI60 is a 1-piece hydrophilic acrylic IOL with 4 flange haptics of the same acrylic material as the optic (Figure 1). Table 1 shows further characteristics of the IOLs.

Figure 1
Figure 1:
Left: Three-piece hydrophobic IOL. Right: One-piece hydrophilic IOL.
Table 1
Table 1:
Characteristics of the IOLs.

Surgery was performed by the same surgeon (R.M.) using a standardized coaxial microincision phacoemulsification technique. In all patients, both eyes were operated on in a single session in an outpatient setting. After topical anesthesia was administered, a posterior limbal self-sealing 1.8 mm incision was created. The anterior chamber was filled with a dispersive ophthalmic viscosurgical device (OVD), and a continuous curvilinear capsulorhexis slightly smaller than the IOL optic diameter was made. After hydrodissection and coaxial phacoemulsification, the folded IOLs were implanted in the bag with an injector. After IOL implantation, the OVD was carefully removed from the anterior chamber and the capsular bag by coaxial irrigation/aspiration (I/A). Care was taken to aspirate all OVD from the bag by slightly tilting up the IOL and positioning the I/A tip behind the IOL optic. Care was taken to completely remove residual cortex fibers adhering to the capsule fornix using biaxial cortex peeling instrumentation if necessary. At the completion of surgery, all optics were circumferentially overlapped by the anterior capsule leaf. Postoperative treatment consisted of topical lomefloxacin (Okacin) 4 times a day for 1 week and diclofenac eyedrops (Voltaren) eyedrops 4 times a day for a minimum of 2 weeks.

Follow-up examinations were performed 1 week, 20 months, and 4 years after surgery and consisted of Snellen corrected distance visual acuity (CDVA) and slitlamp evaluation. On each occasion, patients received phenylephrine 2.5% and tropicamide 0.5% at least 30 minutes before they were examined at the slitlamp. The following aspects were assessed subjectively using a standardized evaluation form: IOL position and centration, capsulorhexis–IOL overlap, and the amount and type of anterior capsule opacification (score 0 to 3). A subjective score of 0 to 10 was used for regeneratory PCO (0 = clear capsule; 10 = severe regeneratory PCO). Finally, the need for an Nd:YAG capsulotomy was noted. The criteria for the necessity of capsulotomy were patient-reported complaints, a CDVA of 20/25 (decimal equivalent 0.8) or less attributable to PCO on slitlamp examination, or both. On each occasion, digital retroillumination images were taken from the posterior capsule for documentation of regeneratory PCO. For this purpose, a photo-acquisition system was used as previously described.5

As the PCO amount was of major interest in this study, automated image-analysis software for objective PCO evaluation was also used. The Automated Quantification of After-Cataract (AQUA) software calculates an objective PCO score between 0 and 10 (0 = clear capsule; 10 = exceptionally severe PCO).6

Data are presented as the mean ± SD or as the median (minimum, maximum). Statistical analyses were computed with SPSS for Windows software (version 18.0, SPSS, Inc.). The CDVA was converted to logMAR notation before statistical analysis. Both eyes of patients who had an Nd:YAG laser treatment before the examination were excluded from the statistical analysis of CDVA and PCO. Paired tests were performed because of the intraindividual design of the study. Numeric and scaled data were analyzed using Wilcoxon tests. Paired categorized data were analyzed with McNemar chi-square tests. A P value less than 0.05 was considered significant.

There were missing data because there were Nd:YAG laser capsulotomies performed after the 20 months but before the 4-year examination. Thus, additional analysis of the 4-year follow-up was performed according to a statistical model described in detail by Buehl et al.7 Instead of excluding from statistical analysis patients who had Nd:YAG treatment, the missing PCO scores were extrapolated assuming 3 scenarios. For the worst-case scenario, the missing value was replaced with the maximum score (10) assuming that the PCO would have increased to the most severe score without a capsulotomy. In the best-case scenario, the value of the 20-month examination was inserted for the missing AQUA score. This assumed that the 20-month AQUA score would not have changed without capsulotomy. The third option was to calculate an estimated value by interpolating the existing PCO values (ie, a linear interpolation of the 2 individual preceding measurements) For example, if PCO increased by 20% between 20 months and 4 years, a missing 4-year PCO score can be estimated by increasing the known 20-month value by 20%; this was considered the estimated value.

Results

The study evaluated 120 eyes of 60 patients. The mean age at surgery of the 41 women and 19 men was 75 ± 8 years (range 57 to 87 years). There were no surgical complications that led to patient exclusion.

Follow-up examinations took place a mean of 21 ± 3 months and 50 ± 3 months after surgery. Thirty-nine patients were available for the 20-month follow-up examination. Dropouts were because of death (2 patients), immobility (3 patients), discontinuation of study (2 patients), inability to contact the patient (6 patients), and the patient’s failure for unknown reasons to respond to the invitation to the follow-up (8 patients). Thirty-four patients were available for the 4-year follow-up. Dropouts were due to immobility (2 patients), discontinuation of study (1 patient), and the patient’s failure for unknown reasons to respond to the invitation to follow-up (2 patients) (Figure 2).

Figure 2
Figure 2:
Dropouts and capsulotomies performed before follow-up (Nd:YAG = neodymium:YAG; PCO = posterior capsule opacification).

Table 2 shows the subjective, objective, and estimated PCO scores in both groups. Twenty months postoperatively, the mean objective PCO score was nearly twice as much in the hydrophilic group as in the hydrophobic group; the difference between the 2 groups was statistically significant (P < .05). After 4 years, the difference in the objective PCO score was not statistically significant different between the 2 groups (P =.272; n = 14) (Table 2 and Figure 3).

Figure 3
Figure 3:
Objective PCO scores in both groups 20 months (n = 35) and 4 years (n = 14) after surgery (PCO = posterior capsule opacification).
Table 2
Table 2:
Main results.

Similar to the objective image analysis findings, the subjective PCO score from the slitlamp examination was statistically significantly lower in the hydrophobic group than in the hydrophilic group at 20 months (P<.01; n = 35) and at 4 years (P =.017; n = 14).

Four years after implantation, 2 (14%) of 14 patients had the same amount of regeneratory PCO in both eyes, whereas 5 patients (36%) had more regeneratory PCO in the eye with the 3-piece hydrophobic IOL and 7 patients (50%) had more regeneratory PCO in the eye with the 1-piece hydrophilic IOL (Figure 4).

Figure 4
Figure 4:
Intraindividual differences in objective PCO score 4 years after surgery (n = 14) (IOL = intraocular lens; PCO = posterior capsule opacification).

The estimated 4-year objective PCO score was statistically significantly lower in the hydrophobic group than in the hydrophilic group at 20 months (P =.001; n = 28) (Table 2 and Figure 5).

Figure 5
Figure 5:
Best, estimated, and worst objective regenerative PCO scores in both groups (n = 28) (IOL = intraocular lens; PCO = posterior capsule opacification).

Before the 20-month visit, 4 patients (10%) had an Nd:YAG capsulotomy in at least 1 eye (5 total capsulotomies), with 4 capsulotomies performed at the Medical University of Vienna. At the 20-month visit, Nd:YAG capsulotomy was performed in 2 additional eyes with a 3-piece hydrophobic IOL and in 9 eyes with a 1-piece hydrophilic IOL. Table 2 shows the overall Nd:YAG capsulotomy rate at 20 months.

Before the 4-year examination, 20 patients (59%) had an Nd:YAG capsulotomy in at least 1 eye (30 total capsulotomies), with 24 capsulotomies performed at the Medical University of Vienna. Over the 4-year follow-up, an Nd:YAG capsulotomy was performed in 7 additional eyes with a 3-piece hydrophobic IOL and in 6 eyes with a 1-piece hydrophilic IOL. Table 2 shows the overall Nd:YAG capsulotomy rate at 4 years.

More capsule folds were observed in the hydrophobic group (12 of 35 [34%]) than in the hydrophilic group (4 of 35 [11%]) 20 months after surgery (P =.039). There was no statistically significant difference in IOL decentration, capsulorhexis–IOL overlap (buttonholing), or patient-described subjective visual symptoms between the 2 groups. No IOL showed glistenings on slitlamp observation. Figure 6 shows 3 representative cases in this dataset.

Figure 6
Figure 6:
Retroillumination images of 3 patients at the first and the second follow-up (IOL = intraocular lens).

The CDVA in eyes without Nd:YAG capsulotomy was significantly better in the hydrophobic group and in the hydrophilic group (0.097 [−0.10, 0.40] versus 0.15 [0, 1.0]) (P =.002; n = 35). Four years postoperatively, the median logMAR CDVA in untreated eyes was 0.097 (range 0 to 0.22) in the hydrophobic group and 0.2 (range 0 to 1.0) in the hydrophilic group (P =.027; n = 14).

Discussion

Posterior capsule opacification was significantly higher in eyes with the MI60 1-piece hydrophilic IOL than in eyes with the 3-piece hydrophobic IOL at the 20-month follow-up. After 4 years, both MICS IOLs presented very high Nd:YAG rates (77% and 50%, respectively) (P =.012) and the estimated PCO score, calculated as described in the Patients and Methods section, was twice as much in the 1-piece hydrophilic IOL group as in the 3-piece hydrophobic IOL group (P =.001). More capsule folds were observed in the hydrophobic group (34%) than in hydrophilic group (11%) 20 months after surgery (P =.039).

In the present study, the Nd:YAG rate was 77% in eyes with the hydrophilic IOL 4 years after surgery. This is in contrast to other reported Nd:YAG rates for conventional hydrophilic acrylic IOLs as follows: 7.6% for the Stabibag (Ioltech)8 and 6.8% for the Akreos Adapt (Bausch & Lomb)9 2 years after implantation. Reported Nd:YAG rates of other hydrophilic acrylic MICS IOLs are 33% for the Thinlens (Technomed GmbH), 33% for the Careflex (w2o Medizintechnik AG), and 20% for the Acri.Smart (Carl Zeiss-Meditec AG) after 2 years10 and 65% for the Thinoptx Ultra Choice (Thinoptx, Inc.) after 15 months.11 Previous studies of the MI60 IOL reported Nd:YAG rates of 20%3 and 36%12 after 1 year. These rates are comparable with our Nd:YAG rate of 31% in eyes with the hydrophilic acrylic MI60 IOL at the 20-month follow-up. However, the observation period in the other 2 studies was much shorter than our long-term follow-up of 4 years and PCO tends to progress over time.

Furthermore, the Nd:YAG rate was 50% in eyes with the hydrophobic acrylic Y-60H IOL 4 years after surgery. Variable but generally lower Nd:YAG rates have been reported with other hydrophobic acrylic IOLs with comparable design and material characteristics as follows: 2.47% for the Acrysof MA60MA13 and 2.7% for the Acrysof MA30BA8 after 2 years and 14% for the Acrysof MA60AC14 and 3.0% for the Acrysof AR40e15 3 years after implantation (all Alcon). We are only aware of 1 study of the Y-60H IOL16 reporting a 5.0% Nd:YAG rate within the very short follow-up (1 year), which would be consistent with our 10.0% Nd:YAG rate at the 20-month control. However, a comparably high Nd:YAG rate of 36.0% has been reported for the hydrophobic acrylic NY-60 MICS IOL (Hoya Surgical Optics) 3 years postoperatively.17

It is well accepted that PCO development is greatly influenced by IOL material and design. Regarding material, many studies comparing square-edged hydrophobic and hydrophilic acrylic IOLs2,18–20 have shown that hydrophilic IOLs perform less favorably than hydrophobic IOLs in terms of PCO prevention.

Second, IOL design must be considered. The IOLs in the present study differ in haptic design. The 3-piece Y-60H IOL has 2 slim, but rigid optic–haptic junctions, while the 1-piece MI60 IOL had 4 flange haptics with a broad optic–haptic junction. The optic–haptic junctions form gateways through which lens epithelial cells (LECs) might access the retrooptical space to form PCO.21 On the other hand, although the slim optic–haptic junctions of the Y-60H IOL appear more favorable, the PMMA haptics seem to be too rigid and oversized for the capsular bag, thus leading to capsular bag ovalization and capsule folds in the axis of the haptics (ie, capsule distension syndrome).22 This is in accordance with our findings of significantly more capsule folds in eyes with the Y-60H IOL. Stretching the capsular bag can lead to insufficient fusion of the anterior capsule and posterior capsule that defies the bending effect of the square edge along the IOL axis. Therefore, the results in our study might not be solely attributable to the difference in IOL material but also to the differences in haptic design.

The stronger PCO development in eyes with the MI60 IOL was probably a result of the hydrophilic acrylic material and deviation from the common 3-piece or 1-piece open-loop haptic designs. The MI60 IOL, with its broad optic–haptic junction, apparently has less of a barrier effect against migrating LECs.

In conclusion, both MICS IOLs yielded high Nd:YAG rates at the 4-year follow-up. Posterior capsule opacification development was more pronounced and the Nd:YAG rates were higher in the MI60 IOL group than in the Y-60H IOL group. Because the 2 IOLs differ in material and design, it is hard to pinpoint 1 deciding reason. Apart from the long follow-up, possible causes of the unusually high PCO and Nd:YAG rates are the broad haptic junctions and lack of a truly sharp posterior edge of the MI60 IOL, which interfere with capsule bend formation, and the overly large and rigid haptics of the Y-60H IOL, which cause oval distortion of the capsule bag. However, for patients to profit from microincision surgery, MICS IOLs must provide a PCO performance comparable to that of conventional IOLs.

What Was Known

  • Hydrophilic IOLs perform less favorably than hydrophobic IOLs in terms of PCO prevention.
  • One-piece IOLs were shown to be as effective as 3-piece IOLs in PCO inhibition.

What This Paper Adds

  • The hydrophobic acrylic 3-piece IOL showed better performance related to the incidence and intensity of PCO and Nd:YAG capsulotomy rate than the hydrophilic acrylic 1-piece IOL.

References

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Other Cited Material

A. U.S. National Institutes of Health Clinical Trials. Posterior Capsule Opacification and Frequency of Nd:YAG Treatment and of Two IOLs: Hoya iMics Y-60H vs. Bausch & Lomb MI60 (MIMI). NCT01786356. Available at: https://clinicaltrials.gov/ct2/show/NCT01786356. Accessed February 7, 2015
© 2015 by Lippincott Williams & Wilkins, Inc.