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Capsular bag stability and posterior capsule opacification of a plate-haptic design microincision cataract surgery intraocular lens: 3-year results of a randomised trial
  1. Nino Hirnschall1,2,
  2. Yutaro Nishi1,
  3. Alja Crnej1,
  4. John Koshy1,
  5. Vinod Gangwani1,
  6. Vincenzo Maurino1,
  7. Oliver Findl1,2
  1. 1Moorfields Eye Hospital NHS Foundation Trust, London, UK
  2. 2Department of Ophthalmology, VIROS—Vienna Institute for Research in Ocular Surgery, a Karl Landsteiner Institute, Hanusch Hospital, Vienna, Austria
  1. Correspondence to Dr Oliver Findl, Moorfields Eye Hospital NHS Foundation Trust, City Road, London EC1V 2PD, UK; oliver{at}findl.at

Abstract

Purpose To compare capsular bag stability and posterior capsule opacification (PCO) of a plate-haptic intraocular lens (IOL) and a standard three-piece open-loop-haptic IOL of the same acrylic material.

Methods In this randomised bilateral patient-masked and examiner-masked study, each patient received a microincision cataract surgery IOL (MICS IOL; Acri.Smart 46S=CT SHERIS 209M) in one eye and a small incision cataract surgery IOL (SICS IOL; AcriLyc 53N = CT 53N, both Carl Zeiss Meditec AG, Germany) as a control in the contralateral eye. Follow-up examinations were performed 1 h, 1 week, 1 month, 1 year and 3 years postoperatively. Anterior chamber depth (ACD) was measured and retroillumination images were performed at all postoperative follow-ups. Furthermore, uncorrected and corrected distance visual acuity, autorefraction and subjective refraction were assessed.

Results In total, 50 eyes of 25 patients were included. The ACD difference between the MICS IOL and the SICS IOL was not significant at any time point (p>0.05). Distance-corrected visual acuity at the 3-year follow-up was similar and not significantly different between the groups (p=0.48). Mean AQUA score in the MICS IOL group and in the SICS IOL group at the 3-year follow-up was 2.3 (SD ±2.3) and 2.1 (SD ±2.2), respectively (p=0.79).

Conclusions The investigated hydrophilic acrylic plate-haptic MICS IOL with a hydrophobic surface showed comparable results concerning capsular bag stability and PCO rates up to 3 years compared with a SICS IOL of the same material.

  • Micro Incision Cataract Surgery
  • Small Incision Cataract Surgery
  • Plate Haptic
  • Capsular Bag Stability

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One of the most recent advances in cataract surgery is microincision cataract surgery (MICS), where an incision size of 2.0 mm and less is used, whereas for small incision cataract surgery (SICS), an incision size of about 2.5 mm is typically used. For MICS, the lens material is emulsified either bimanually or with a thin single coaxial handpiece. The potential advantages are lower-induced corneal astigmatism,1 possibly a lower incidence of infection due to higher resistance of the wound to deformation2 and a lower risk of complications such as iris prolapse during surgery in patients at risk such as with intraoperative floppy iris syndrome (IFIS). However, currently there are only few intraocular lens (IOL) models that are implantable through such small incisions. The current MICS-compatible IOL models that are injectable through the small incisions typically have a plate-haptic type of design to centre the IOL in the capsular bag similar to the first foldable silicone IOLs in the 1980s.3 The current standard designs for SICS IOLs are either single-piece or multipiece open-loop haptics, which not only ensure good centration within the capsular bag but also axial stability that determines postoperative refractive stability,4 as well as good performance regarding inhibition of posterior capsule opacification (PCO) when coupled with a sharp posterior optic edge.5

Monobloc MICS IOLs are thought to potentially have a higher incidence of PCO due to lack of bending of the posterior capsule at the sharp optic edge due to the broad haptic–optic junction zone, which may allow lens epithelial cells (LECs) to migrate behind the IOL optic.6 Additionally, MICS IOLs tend to be made of hydrophilic acrylic material, which, due to its mechanical properties, appears to be more suitable for implantation through very small IOL injector systems. Higher PCO rates have been shown for hydrophilic materials7 possibly due to either the material properties per se or the less sharp optic edge compared with hydrophobic materials. IOL haptic design is crucial for maintaining axial and rotational stability of the IOL.8

The aim of this study was to compare capsular bag stability and PCO development of a plate-haptic IOL and a standard three-piece open-loop-haptic IOL made of the same acrylic material over a long-term follow-up.

Methods

This randomised bilateral patient-masked and examiner-masked study included patients who were scheduled for bilateral cataract surgery. Inclusion criteria were age 40 or older and best distance-corrected visual acuity better than 1/20 Snellen. Exclusion criteria were pseudoexfoliation syndrome, glaucoma or retinal degenerations. All the research and measurements followed the tenets of Helsinki, and the study was approved by the local ethics committee in London. Informed consent was obtained from all patients prior to the procedure.

Each patient received a MICS IOL (Acri.Smart 46S = CT SHERIS 209M) in one eye and a SICS IOL (AcriLyc 53N = CT 53N, both Carl Zeiss Meditec AG, Germany) as a control in the contralateral eye to allow for intraindividual comparison. The second eye was operated within 4 weeks’ time. The first eye was randomised to the IOL type using an envelope method. Randomisation was performed using a computer system by a person otherwise not involved in the trial. Patients and examiners were masked to allocation, and the surgeon was masked to allocation until the time of IOL implantation.

Investigated IOLs and surgery

The MICS IOL used in this trial is a single-piece IOL, with a 6.0 mm equiconvex optic and an overall length of 11.0 mm. The IOL is not angulated and the haptic and optic design shows square-truncated edges. The material is a foldable acrylate copolymer with ultraviolet absorber, 25% water content in fully hydrated status and a hydrophobic surface. The optimised A-constant for SRK/T IOL power formula is 118.3, and the refractive index of the IOL (dry) is 1.51 and 1.46 after hydration. The edge thickness is in the range 0.25–0.27 mm.9 The refractive outcome and visual performance of this IOL have been shown to be good.10 ,11

The control SICS IOL (AcriLyc 53N) consists of the same material as the MICS IOL.

It is a three-piece loop-haptic IOL with a biconvex 6.0 mm optic and a total diameter of 13.0 mm. The C-loop haptics are polymethyl methacrylate and have an angulation of 5°.

All patients were operated using standard small incision phacoemulsification technique by two surgeons (OF and VM). The two eyes of each patient were operated by the same surgeon. In all cases, a temporal incision of 2.5 mm was performed. The anterior chamber was filled with a viscoelastic device and a continuous curvilinear capsulorhexis was created of a size to allow a 360° rhexis–IOL overlap after IOL implantation. After hydrodissection and phacoemulsification, the surgeon was unmasked to the IOL type. The folded IOLs were implanted in the bag with the dedicated injector devices. After IOL implantation, care was taken to completely remove the viscoelastic device from behind the IOL, the bag and the anterior chamber. Postoperative treatment consisted of dexamethasone and chloramphenicol eye drops four times daily for 4 weeks.

Preopertive and postoperative examinations

Prior to surgery, partial coherence interferometry technology (IOL-Master software V.5.1; Carl Zeiss Meditec AG, Germany) was used to measure axial length of the eye and K-readings of the cornea. SRK/T formula was used to calculate the IOL power and target refraction was emmetropia (0.0D to −0.5D) or −2.5D for patients who wanted to stay myopic after cataract surgery.

Follow-up examinations were performed 1 h, 1 week, 1 month, 1 year and 3 years postoperatively.

Anterior chamber depth (ACD) was measured using partial coherence interferometry (AC-Master, Carl Zeiss Meditec AG, Germany) 1 h, 1 week, 1 month and 1 year after surgery.

Uncorrected and corrected distance visual acuity were determined using backlit ETDRS charts (Precision Vision, USA) at 4 m; autorefraction in IOL mode (Topcon Corporation, Tokyo, Japan) and subjective refraction using the cross-cylinder method were performed at each follow-up.

A subjective score of 0–3 was used to analyse anterior capsular opacification (ACO) at the slit lamp.

To assess PCO, rhexis size and IOL centration, retroillumination images were performed at all postoperative follow-ups. For this purpose, we used a digital camera (EOS 5D, Canon, Japan) mounted on a modified Zeiss 30 slit lamp (Carl Zeiss Meditec AG, Germany) with an external flashlight source, which provides coaxial illumination from a flash pack through a fibre-optic cable to the camera.12 It produces even illumination over the entire image with relatively small flash artefacts, and it was shown to be highly reproducible.13 All digital images were transferred to a personal computer and were stored on a hard disc for evaluation later. PCO was objectively evaluated measuring the entropy of the retroillumination images using an automated image analysis software (AQUA)14 with a score between 0 and 10, where 0 indicates a clear capsule and 10 indicates severe PCO. Furthermore, the AQUA software gives the rhexis area. In the results section, the rhexis diameter is mentioned (defined as d=2*√(A/π)). Additionally, the centration of the IOL was observed in all retroillumination images.

Statistical analysis

For statistical analysis, Microsoft Excel 2008 for Mac (Microsoft, USA) with a Statplus:mac V.5.8.3.8 plug-in (AnalystSoft, USA) was used, as well as SPSS V.19.0 for Mac (IBM, USA). Descriptive data are always shown as mean, 95% CI of the mean, SD and range. For bilateral comparison, the paired t test and the Wilcoxon test were used (depending on the fact if the results were normally distributed or not). Non-metric data were compared using a χ2 test. To compare measurements of the same eye at different time points, the analysis of variance/analysis of covariance for repeated measurements was used. Furthermore, scatter plots, box plots and error bars were used to compare the two different IOLs.

Results

In total, 50 eyes of 25 patients were recruited for this study. The mean age of all patients was 69.0 years (SD 7.2). Three patients had to be excluded due to complications (in one case the IOL was implanted in the sulcus, in one case a rupture of the posterior capsule occurred and in one case a capsular distension syndrome was observed postoperatively), and one patient did not want to continue with the study after the first eye was operated. Out of these 21 patients, 17 patients attended the 1-year follow-up and 16 patients the 3-year follow-up (two patients moved back to their original countries, one patient could not attend due to general health problems, one patient changed his address and could not be contacted and one patient did not want to attend the 1-year follow-up).

ACD for the MICS IOLs and SICS IOLs is shown in table 1 and figure 1A,B. The difference between the MICS IOL and the SICS IOL was not significant at any time point (1 h: p=0.81; 1 week: p=0.66; 1 month: p=0.87 and 1 year: p=0.68).

Table 1

Anterior chamber depth for MICS and SICS IOLs at different time points

Figure 1

(A) Correlation of the anterior chamber depth (ACD) change in the first year for the microincision cataract surgery intraocular lens (MICS IOL) eye (x-axis) and the small incision cataract surgery IOL (SICS IOL) eye (y-axis) for each patient. The triangle depicts the mean ACD shift in the first year after surgery. (B) ACD in mm for the MICS IOL (black) and the SICS IOL (grey). The dots of the error bars show the mean, and the whiskers show the SD.

Distance-corrected visual acuity at the 3-year follow-up was similar and not significantly different (p=0.48) between groups (MICS IOL group: −0.04 log MAR; CI: ±0.08; SD: ±0.19; SICS IOL group: −0.04 log MAR; CI: ±0.08; SD: ±0.17).

At the 3-year follow-up, severe, moderate, mild and no ACO were observed in 7%, 36%, 57% and 0% in the MICS IOL group and 0%, 43%, 57% and 0% in the SICS IOL group (n=32 eyes), respectively. These differences were not found to be significant (p=0.62).

The mean AQUA scores for PCO in the MICS IOL and in the SICS IOL groups at the 3-year follow-up were 2.3 (CI: ±0.4; SD: ±2.3; max: 5.6) and 2.1 (CI: ±0.5; SD: ±2.2; max: 6.4; figure 2), respectively (n=26 eyes). This difference was not found to be significant (p=0.79). In total, six eyes needed an Nd:YAG laser capsulotomy between the 1-year and the 3-year follow-up, three eyes in the MICS IOL group and three eyes in the SICS IOL group (these eyes were not analysed with the AQUA software). Furthermore, no statistically significant differences were found concerning rhexis size at the 3-year follow-up (MICS group: 4.9 mm; SD 0.4 mm and SICS IOL group: 4.9 mm; SD 0.3 mm; p=0.52). In none of the cases, a relevant decentration (more than 1.0 mm) was observed.

Figure 2

Posterior capsule opacification (PCO) score (AQUA) for the microincision cataract surgery and the small incision cataract surgery intraocular lens for all eyes that had not undergone Nd:YAG capsulotomy at the 3-year follow-up (n=26 eyes). Maximum AQUA value is 10 (severe PCO) and minimum is 0 (no PCO).

Discussion

The introduction of MICS in cataract surgery results in a significant reduction in surgically induced astigmatism1 and potentially a higher resistance of wound to deformation.2 However, MICS IOLs have to fulfil special requirements concerning tolerance to high compression during the implantation process additionally to a good capsular bag stability and low PCO rates.9 The plate-haptic MICS IOL used in this study fulfilled these requirements concerning foldability, not showing any visible damage when injected with a special MICS injector.15 Furthermore, Prinz et al16 showed that the MICS IOL used in our study was stable within the capsular bag concerning rotation, which is relevant for toric designs of this IOL.

However, ACD shift of this MICS IOL has not been studied previously. In our study, the plate-haptic MICS IOL showed a slight backward shift in the first month that was not found to be more pronounced compared with the SICS IOL. During the 1-month and the 1-year follow-up, the IOL shifted slightly forward to result in a very similar ACD compared with the control SICS IOL at the 1-year follow-up. Similar findings were found for another plate-haptic IOL.4 Wehner et al10 observed good refractive outcomes after implanting the same IOL model used in our study. However, the refractive outcome is a weak variable to assess ACD shift of an IOL postoperatively because subjective refraction is not an accurate method and the impact of the same ACD shift on the refractive outcome is different in short compared with long eyes.

PCO results for the MICS IOL were not significantly different compared with the control SICS IOL in this study. Similar Nd:YAG rates were observed by Spyridaki et al,17 who observed an Nd:YAG rate of 20% 850 days after cataract surgery. This low PCO score could be explained by the relatively large edge thickness of the plate-haptic IOL (250–270 µm9) that serves as a mechanical barrier for the lens epithelial cells.18 Another explanation for the low PCO score could be the hydrophobic surface properties of the MICS IOL and may also result in a sharper optic edge compared with other hydrophilic acrylic IOLs.

This study showed that the investigated hydrophilic acrylic plate-haptic MICS IOL with a hydrophobic surface showed comparable results concerning capsular bag stability and PCO rates up to 3 years after surgery compared with a SICS IOL of the same material.

Acknowledgments

The authors acknowledge a proportion of their financial support from the Department of Health through the award made by the National Institute for Health Research to Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology for a Specialist Biomedical Research Centre for Ophthalmology. The views expressed in this publication are those of the authors and not necessarily those of the Department of Health.

References

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Footnotes

  • Contributors NH was responsible for the measurements, analysis and writing the manuscript. YN, AC, VG and JK were responsible for the measurements and recruiting patients. VM was responsible for the surgery and manuscript corrections. OF was responsible for the concept, study design, surgery, analyses and manuscript corrections.

  • Competing interests None.

  • Ethics approval Moorfields—Ethics Committee, London, UK.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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