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Posterior Capsule Opacification After Phacoemulsification: Annual Review

Vasavada, Abhay R. MS, FRCS (England); Praveen, Mamidipudi R. DOMS

The Asia-Pacific Journal of Ophthalmology: July/August 2014 - Volume 3 - Issue 4 - p 235–240
doi: 10.1097/APO.0000000000000080
Annual Review
Free
Editor's Choice

Purpose The purpose of this article is to provide a clinical update on posterior capsule opacification (PCO) after phacoemulsification by reviewing the literature from the last 12 months.

Design This article is a literature review.

Methods The authors conducted a 1-year literature search in the English language on PCO using PubMed. The period used to conduct the literature search was from January 1, 2013, to January 1, 2014. The following search terms were used during the PubMed search: phacoemulsification, microcoaxial incision, posterior capsule opacification, long-term evaluation of intraocular lens (IOL) implantation, IOL edge design and material, surgical technique, anterior capsule overlap on the IOL optic, diabetes mellitus, myopia, pseudoexfoliation, retinitis pigmentosa, uveitis, and neodymium: yttrium-aluminum-garnet laser capsulotomy.

Results This review incorporates original articles that provided fresh insights and updates on PCO. Particular attention was paid to observational, randomized, controlled clinical trials, as well as analyses of larger cohorts with a prospective and retrospective study design. Letters to the editor, unpublished works, experimental trials and abstracts were not considered.

Conclusions This annual review provides a brief update on PCO that might be of interest to the practicing clinical ophthalmologist.

From the Iladevi Cataract and IOL Research Center, Raghudeep Eye Clinic, Ahmedabad, India.

Received for publication March 25, 2014; accepted July 2, 2014.

Reprints: Abhay R. Vasavada, MS, FRCS, Iladevi Cataract and IOL Research Center, Raghudeep Eye Clinic, Gurukul Rd, Memnagar, Ahmedabad 380052, India. E-mail: icirc@abhayvasavada.com.

Cataract is the leading cause of blindness worldwide, despite the availability of effective cataract surgery.1,2 In the developed world, cataract treatment and rehabilitation are managed satisfactorily, but in developing countries, up to 20 million individuals are waiting to undergo cataract surgery and 14,000 new patients are added to the list every day.3,4 Manual small-incision cataract surgery and phacoemulsification are the most frequently performed surgical procedures in the developed countries. They provide quick restoration of vision. However, they can lead to complications such as the development of secondary cataract, which is also known as posterior capsular opacification (PCO).5–11 This is a major medical problem impacting the patient’s well-being because it can lead to decreased visual acuity. In spite of improvements in basic research on the development of cataract, surgical techniques, as well as the material or the design of the intraocular lens (IOL), the incidence of PCO is still 8% to 34.3% in adults and nearly 100% in children.12–17 Decreased visual acuity induced by PCO is reported to occur in 20% to 40% of patients 2 to 5 years after surgery.8,18 The most common and indeed successful method of treatment of PCO is to photodisrupt a section of the posterior capsule using a high-energy Nd:YAG laser to create a clear region around the visual axis.19 This treatment is expensive, costing the US Medicare program millions of dollars. It can also lead to a host of medical complications such as an increase in intraocular pressure, retinal detachment, cystoid macular edema, and, in the extreme cases, pitting of the surface and fracture of the intraocular lens adjacent to the cleared region.20–22 The technology to perform YAG laser capsulotomy is frequently unavailable in underdeveloped countries, adding considerably to the problems of eradicating cataract-induced blindness in these countries. The clinical and economic significance of PCO makes it an important public health problem. In order to prevent it, a clear understanding of the pathogenesis is needed.23,24

Posterior capsular opacification is a wound-healing response of the residual equatorial lens epithelial cells (LECs), which are inevitably left in the bag and then undergo proliferation, migration, and metaplasia. These residual LECs can be clinically differentiated into 2 types: fibrotic and regeneratory LECs. Transdifferentiation of residual LECs into myofibroblasts causes fibrotic PCO. Migration of LECs into the space between the capsule and the IOL with subsequent proliferation causes regeneratory PCO. Clinically, the anterior LECs surrounding the rhexis express alpha smooth muscle actin and become myofibroblasts. The equatorial cells form Elschnig’s pearls. However, a biological understanding of the reason for this is lacking. Both fibrotic PCO and regeneratory PCO can lead to visual loss once the visual axis has been involved.

This review incorporates only a selected number of articles involving clinical trials in the English-language literature. All articles included in this review were listed in PubMed between January 2013 and January 2014, including large retrospective and prospective, comparative, observational, and randomized trials on IOLs, surgical techniques, and ocular diseases after phacoemulsification. Only clinically relevant, novel, and potentially important and original research has been included. The goal is to provide a comprehensive and in-depth assessment of findings in the field of PCO.

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Posterior Capsule Opacification With Coexisting Ocular Disease

There is a noticeable decline in the occurrence of PCO due to improved surgical techniques and IOL technology. Despite these improvements, the development of PCO in patients undergoing cataract surgery is influenced by the presence of systemic conditions such as diabetes, pseudoexfoliation (PEX), uveitis, and retinitis pigmentosa (RP).

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Posterior Capsule Opacification and Pseudoexfoliation

Østern et al25 carried out a long-term evaluation of patients for the development of PCO. Patients with and without PEX were evaluated using retrospective records of patients with PEX, who had undergone cataract surgery between June 2001 and December 2002. The authors compared 44 patients with PEX to 86 patients without PEX to assess the development of PCO 6 to 7 years after phacoemulsification. A standardized surgical procedure was implemented. The images were analyzed using a software program (POCOman) to determine the extent and severity of PCO. Using the guidelines available for POCOman, PCO was defined as any formation of pearls or fibrous opacification, visible on the retroilluminated JPEG-formatted images.

When the analyses were based on the (estimated) edge of the IOL and capsulorhexis, there were statistically significant differences between the 2 groups concerning severity and percentage of PCO (Mann-Whitney U test, P = 0.01 and P = 0.02). There was a lower level of PCO in eyes with PEX. Percentage and severity of PCO within the central 4.0- and 1.3-mm optical zones were compared between the 2 groups. The results were not statistically significant. An additional multivariate linear regression analysis was conducted. The percentage and severity of PCO was not statistically significant in both groups. Neodymium:yttrium-aluminum-garnet capsulotomy was performed in 16% (n = 7) of eyes in both groups (chi-square test, P = 0.96). In eyes with PEX undergoing phacoemulsification, there was a reduced risk for incurring an inflammatory response. The authors assumed that since the initial inflammatory response was minimal, it acted as a weaker stimulus for the development of PCO in eyes with PEX.

This study employed a semiobjective method to assess the long-term development of PCO in eyes with PEX. Although PEX is associated with a varied spectrum of complications, Ostern et al provided objective evidence of a decreased incidence of PCO after cataract surgery. Importantly, they implemented standardized surgical techniques for in-the-bag AcrySof IOL fixation and postoperative medication. This standardization helped objectively evaluate whether the patients with PEX ran the risk of developing PCO. In conclusion, this study showed that at the end of 6 years, the presence of PEX did not increase the risk of PCO development when compared with patients without PEX. Patients with PEX did not need PCO treatment more frequently than patients without PEX.

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Posterior Capsule Opacification and Retinitis Pigmentosa

Dikopf et al,26 in their retrospective observational case series, evaluated surgical outcomes in patients with RP undergoing phacoemulsification. Generally, it is difficult to predict visual outcomes when both lenticular and retinal pathologies coexist. There is also a high risk for postoperative complications while performing surgery on patients with RP. One of these complications is PCO.

In this study, the authors reviewed cataract extraction in a large group of patients with RP. Special attention was drawn to the outcomes and complications of surgical intervention. Between 2002 and 2012, 80 eyes of 47 consecutive patients with RP underwent phacoemulsification with IOL implantation. Postoperative records were analyzed for incidence of PCO, ND:YAG capsulotomy, and surgical complications. The mean follow-up time was 23.3 months. Sixty-six (82.5%) eyes developed some level of PCO and 42 (52.5%) eyes required a YAG posterior capsulotomy at an average of 10.8 months after surgery. Fifteen patients had less than 3 months of follow-up. A Kaplan-Meier survival curve was created to better describe the development of significant PCO and the need for a YAG capsulotomy. There was a high occurrence of YAG capsulotomy in RP patients with RP after cataract extraction. A majority of the patients required YAG capsulotomy within a year after surgery. An increased rate of PCO is quite normal in any population of young patients undergoing cataract extraction. However, PCO can be exacerbated by known disruptions of the blood-ocular barrier in patients with RP, allowing for high aqueous levels of interleukin 1 to accumulate after surgery.

There were high PCO rates in patients with RP due to zonular laxity. It allowed posterior capsule wrinkling proir to capsular phimosis, providing an effective network for migration of lens epithelial cells (LEC). Aggressive capsule polishing by simple or ultrasound aspiration, osmolysis, or even usage of a capsular tension ring was often suboptimal in preventing PCO in patients with RP. One of the strengths of this study is the use of a large sample of patients with RP operated on by a single surgeon. However, the study has its limitations. The most significant limitation is the use of a retrospective design. Another limitation is the use of both eyes although the use of a single eye of each patient would have been scientifically more valid. The rates of PCO and YAG capsulotomy (82.5% and 52.2%, respectively) confirm this known complication of cataract surgery in patients with RP.

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Posterior Capsule Opacification and High Myopia

Zhao et al27 attempted to understand the mechanisms affecting the development of PCO in highly myopic eyes by using ultra-long scan depth optical coherence tomography (UL-OCT). They compared highly myopic eyes with emmetropic eyes for capsule-IOL interactions, including anterior and posterior capsule adhesion and configuration of the capsular bend. Various configurations of capsular bend with the IOL were observed at the last follow-up. They were classified into complete and incomplete capsular bends. Three different types of complete capsular bends by UL-OCT were described postoperatively. The first was anterior adhesion in which the anterior posterior capsule was attached to the anterior side of the optic. The second was middle adhesion in which the anterior posterior capsule was attached to the middle of the optic, and the third was posterior adhesion in which the anterior posterior capsule was attached to the posterior side of the optic. Three different types of incomplete capsular bends by UL-OCT were also described postoperatively. The first was funnel adhesion in which the anterior posterior capsule was attached to the middle of the optic at a distance from the IOL. The second was parallel adhesion, in which the anterior posterior capsule did not attach completely. Finally, the third was furcate adhesion in which the anterior posterior capsule was separated peripherally although the capsular bend was formed at the edge of the IOL.

This prospective study included 40 eyes of 40 patients with cataract scheduled for phacoemulsification with a single-piece AcrySof IOL implantation (Alcon Laboratories, Inc, Fort Worth, TX, USA). Among the 40 eyes, 20 were highly myopic (axial length >26 mm; high myopia group) and the other 20 were emmetropic with a normal axial length (22 mm < axial length < 24.5 mm; emmetropia group). Three types of capsular bends with complete adhesion were found in highly myopic eyes. Anterior adhesion was observed in most cases (70%). In highly myopic eyes, 4 capsular bends were observed with middle adhesion, while only 1 nasal capsular bend was found with posterior adhesion. Three types of capsular bends with incomplete adhesion were found at the last follow-up in highly myopic eyes. Six capsular bends presented funnel adhesion, 8 capsular bends presented parallel adhesion, and 1 capsular bend showed furcate adhesion. Three types of capsular bends with complete adhesion were found in highly myopic eyes. Anterior adhesion was observed in most cases (70%). In highly myopic eyes, 4 capsular bends were observed with middle adhesion, whereas only 1 nasal capsular bend was found with posterior adhesion. Three types of capsular bends with incomplete adhesion were found at the last follow-up in highly myopic eyes. Six capsular bends presented funnel adhesion, 8 capsular bends presented parallel adhesion, and 1 capsular bend showed furcate adhesion. There was significantly less apposition of the posterior capsule against the IOL in highly myopic eyes when compared to emmetropic eyes. Posterior capsular adhesions were delayed in highly myopic eyes during the follow-up. At the 28-day follow-up, slight PCO was found in 5 highly myopic eyes because the posterior capsule did not adhere completely to the IOL. The rate of posterior capsule adhesion in eyes with a high degree of axial myopia was significantly lower than that observed in emmetropic eyes. The authors speculated possible reasons for this. The IOLs were implanted in relatively large capsular bags in the high myopia group. The capsular bag diameter correlated positively with the axial length, while IOL thickness correlated with IOL power. Secondly, a lower IOL power resulted in reduced posterior convexity. A large-sized posterior capsule with steep convexity could affect posterior capsular adhesion to the IOL. These two factors may have weakened the ability of the capsule to stretch after IOL insertion in highly myopic eyes. A noteworthy observation was that the types of capsular bend were more heterogeneous in the high myopia group and displayed incomplete apposition when compared to the emmetropia group.

This was a prospective study exploring the dynamics of PCO development in highly myopic eyes. The study objectively documented the apposition of the posterior capsule to the IOL using a custom-built, UL-OCT device. The development of PCO could have been attributed to the incomplete formation of capsular bends in highly myopic eyes during the early postoperative period, coupled with weak adhesion between the posterior capsule and the IOL. Capsular bend formation has long been considered crucial for PCO prevention. The authors further speculated that highly myopic eyes with incomplete capsular bend could have facilitated LEC migration. Delayed or incomplete capsule-IOL interaction is believed to increase LEC proliferation and migration due to weak adhesion. There are potential limitations to this study. First, the authors evaluated the procedure for only 28 days postoperatively. Secondly, the sample size was too small. Thirdly, even though the authors observed the capsule-IOL interaction spatially, it was not possible to calculate the space due to the technical limitations of OCT.

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Posterior Capsule Opacification With Alternate Surgical Techniques

Trypan Blue Injection and Posterior Capsule Opacification

Today, the focus of combating PCO is on the lysis of LECs. In a prospective, randomized, clinical trial of patients undergoing phacoemulsification with foldable IOL implantation, Sharma et al coauthors studied the effect of injecting 0.1% trypan blue into the capsular bag on the development of PCO.28 Eyes were randomized into 2 groups, the trypan blue group or the control group. The trypan blue group received 0.2 mL of 0.1% trypan blue (Visiblue; Shah & Shah) injected subcapsularly at 2 sites that were 180 degrees apart after cortical-cleaving hydrodissection. The control group received 0.2 mL of a balanced salt solution injected in a similar fashion and a second injection of balanced salt solution after cortical-cleaving hydrodissection so that the total quantity of fluid in the bag was the same in both groups. A single surgeon performed all surgeries using topical anesthesia and a standardized surgical technique. A foldable hydrophilic acrylic square-edged IOL (CT ASPHINA 603P; Carl Zeiss Meditec) was implanted with a wound-assisted delivery. An anterior segment photograph under full mydriasis was taken at 6 and 12 months. Posterior capsular opacification grading was done. The PCO score was significantly lower in the trypan blue group when compared to the control group at 6 and 12 months.

This study demonstrated the role played by trypan blue in inhibiting PCO. However, a major limitation is the small sample size used. Another limitation is that PCO had been evaluated for over 1 year instead of the customary 3-year duration. A study with a larger sample size carried out over a longer duration is warranted to conclusively ascertain the long-term effects of trypan blue on PCO formation.

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Phacovitrectomy and Posterior Capsule Opacification

Iwase et al29 evaluated PCO development in eyes with idiopathic epiretinal membranes (ERMs) undergoing 20-gauge phacovitrectomy (n = 20 eyes), 23-gauge phacovitrectomy (n = 20 eyes), and phacoemulsification alone (n = 50 eyes). The duration of follow-up was 24 months. After administration of retrobulbar and peribulbar anesthesia, a half-round fornix-based conjunctival incision was created in the 20-gauge phacovitrectomy group. A 3-mm self-sealing sclerocorneal tunnel was created at 12 o’clock in eyes in all the groups. A standardized surgical technique of phacoemulsification was implemented. The wound was not enlarged and the SA60AT IOLs were inserted in the capsular bag. Sutures were not used to close the sclerocorneal tunnel incision. After making 3 scleral ports in the 23-gauge phacovitrectomy group, vitrectomy and ERM peeling without staining were performed. Each sclerotomy was then closed with a 7.0 suture in the 20-gauge phacovitrectomy group. Finally, the conjunctival wound was sutured in the 20-gauge phacovitrectomy group. Suturing was not required in the 23-gauge phacovitrectomy group. The PCO density value was measured using Scheimpflug video photography (EAS-1000; NIDEK, Gamagori, Japan) at 1 week, 1 month, 3, 6, 12, 18, and 24 months after surgery.

The PCO value of the 20-gauge phacovitrectomy group was significantly higher than that of the 23-gauge phacovitrectomy group at 6, 12, 18, and 24 months after surgery. Similarly, the PCO value in the 23-gauge phacovitrectomy group was significantly higher than that of the cataract surgery group at 24 months after surgery. The same IOL, SA60AT, was implanted in all the cases, indicating that the surgical procedure was the only difference among the groups. In this report, similar procedures were performed for each ERM case, namely, cataract surgery, core vitrectomy, and ERM peeling. The reduced incidence of PCO could be attributed to the small size of the vitrectomy instruments used, which lowered postoperative intraocular inflammation. As vitrectomy was less traumatic, the procedure did not seem to cause strong inflammation. There were no significant differences in postoperative intraocular inflammation between the 23-gauge phacovitrectomy and the cataract surgery groups. Despite this, there was an incidence of PCO in the 23-gauge phacovitrectomy group.

To the best of our knowledge, this is the first report quantifying PCO in phacovitrectomy using non-qualitative methods (EAS-1000, Scheimpflug camera). As selection bias had been minimized, the differences between the characteristics of patients and the kinds of retinal diseases could not affect the resultant outcomes. Minimization of selection bias is crucial to any study of this kind. There are many variables that can be associated with PCO development such as the occurrence of intraoperative and/or postoperative complications, usage of long-acting gas tamponade, and postoperative posturing. We speculate that the posterior pressure in eyes without a vitreous may have prevented capsular bend formation that requires a sharp optic edge and posterior pressure. It is, therefore, possible that the IOL edge has a minimal effect in reducing PCO in phacovitrectomy. In addition, a high level of postoperative inflammation may probably lead to LEC migration and extensive PCO in eyes undergoing phacovitrectomy. As this study included only cases with ERMs, these results may only apply to similar cases that have not undergone additional procedures, such as laser photocoagulation or gas tamponade. Further studies are warranted to examine the development of PCO between patients undergoing 25-gauge phacovitrectomy and cataract surgery.

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Intraocular Lens and Posterior Capsule Opacification

Posterior Capsule Opacification With the iMics1 NY-60 and AcrySof SN60WF: 3-Year Results of a Randomized Trial

Leydolt et al30 conducted a prospective, randomized, and controlled study comparing PCO development between two hydrophobic acrylic single-piece, sharp-edged IOLs with a follow-up period of 3 years. One hundred patients (200 eyes) were included in this trial. Each patient randomly received an iMics1 NY-60 IOL (Hoya Corp, Tokyo, Japan) in 1 eye and an AcrySof SN60WF IOL (Alcon Laboratories, Inc, Fort Worth, TX) in the contralateral eye to allow for intraindividual comparison. A single surgeon performed the surgeries using a standardized technique. Follow-up examinations were performed at 1 week and 3 years after surgery. At each follow-up visit, the amount and type of regeneratory PCO were evaluated. Digital retroillumination images of the posterior capsule were captured. Posterior capsular opacification levels were analyzed using automated image analysis software (Automated Quantification of After-Cataract [AQUA]). At 3 years, the PCO score on a scale from 0 to 10 was 3.0 ± 2.0 in the iMics1 NY-60 group and 1.9 ± 1.4 in the AcrySof SN60WF group. The difference between the 2 groups was statistically significant (P < 0.001). However, 46 eyes (82%) in the iMics1 NY-60 group and 9 eyes (16%) in the AcrySof SN60WF group showed a high level of regeneratory PCO. After the 3-year follow-up, the rates of Nd:YAG laser capsulotomy in iMics1 NY-60 was significantly higher when compared against the AcrySof SN60WF eyes (P < 0.001). The results demonstrated that 3 years after surgery, eyes with iMics1 NY-60 IOLs showed a statistically significantly higher PCO score (3.0 ± 2.0) and Nd:YAG capsulotomy rate (35.6%) than those with AcrySof SN60WF IOLs (PCO, 1.9 ± 1.4; Nd:YAG, 13.7%). The authors did not observe a lower incidence of PCO in the eyes with the iMics1 NY-60 IOL compared to the eyes with the AcrySof SN60WF IOL. On the contrary, the iMics1 NY-60 IOL presented a statistically significant higher Nd:YAG capsulotomy rate (35.6%) 3 years after surgery. In conclusion, the present study indicates statistically significant differences in the rate of PCO and Nd:YAG capsulotomy between 2 similarly designed sharp-edged, single-piece IOL models. These disparities can be attributed to differences in their material properties.

The results of this study have shown that IOL materials play an important role in PCO formation. The various hydrophobic acrylic IOLs differ not only in the techniques used in their manufacture, but also in the postprocessing modifications of their surface. It is evident that the properties of the materials used in IOLs impact biological responses such as capsular biocompatibility and LEC migration. An analysis of the surface of AcrySof IOLs revealed a significantly higher magnitude of surface roughness or morphological changes. Another important factor is adhesion of the IOL surface to the capsular bag mediated by extracellular matrix proteins. Better adhesion is assumed to result in less LEC growth between the IOL surface and the capsular bag, causing a lower level of PCO. In vitro studies have shown that hydrophobic acrylic IOLs bind fibronectin to a statistically significantly greater degree than other IOL materials. Thus, fibronectin seems to act as a biological glue with these IOLs resulting in a lower level of PCO. A limitation of the present study is that no additional follow-up visits scheduled between 1 week and 3 years after surgery. An in-between follow-up visit would have allowed a PCO value to be estimated for those eyes so as to demonstrate viability of laser capsulotomy at the 3-year follow-up.

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Posterior Capsule Opacification With 3 Intraocular Lenses: 12-year Prospective Study

Most PCO studies have a follow-up duration ranging from 1 to 3 years, and there are a few studies with a 5-year follow-up. There are very few data available in the literature on PCO development on a long-term basis.

This study was an extended follow-up of a randomized trial whose earlier outcomes at 2, 3, and 5 years have already been reported. Rønbeck et al31 in this prospective study compared PCO formation after implantation of 3 IOL models 12 years after surgery. Using a randomization protocol, the surgeon implanted 1 of the following 3 IOLs: a heparin-surface-modified poly (methyl methacrylate) (HSM PMMA) IOL (809C; Pharmacia & Upjohn, Inc.), a foldable silicone IOL (SI-40NB, Allergan, Inc.), or a foldable hydrophobic acrylic IOL (AcrySof MA60BM; Alcon Laboratories, Inc.). At the follow-up examinations, 11.3 to 13.4 years postoperatively, POCOman system was used to analyze PCO in retroillumination images of the posterior capsule. The percentage of PCO in the total area of the posterior capsule inside the capsulorhexis was the PCO fraction. The number of patients undergoing Nd:YAG capsulotomy during the extended follow-up period and the timing of this treatment after surgery were recorded. After 12 years, there was no significant difference in the fraction or severity of PCO between the silicone and acrylic IOLs. The HSM PMMA IOL had a significantly higher PCO fraction than the silicone IOL (P < 0.05) but not higher that of the acrylic IOL. There was no difference in the severity of PCO between the HSM PMMA IOL and the other 2 IOLs. The silicone IOL had a higher median capsulotomy-free survival (>150 months) than the acrylic IOL (108 months) and the HSM PMMA IOL (53 months). Survival without Nd:YAG capsulotomy did not differ between the acrylic and the silicone IOLs or between the silicone and the HSM PMMA IOLs; however, overall survival was significantly better with the acrylic IOL than with the HSM PMMA IOL (P < 0.001). The PCO evaluation using the retroillumination photographs showed that over time, the differences between the IOLs became increasingly lower. Regarding the overall survival without Nd:YAG capsulotomy over the entire 12-year postoperative period, the sharp-edged hydrophobic acrylic IOL and the round-edged silicone IOL seemed to induce less PCO than the round-edged HSM PMMA IOL. After approximately 6 to 7 years, the survival curve of the silicone IOL crossed that of the hydrophobic acrylic IOL. Subsequently, it had better survival without Nd:YAG capsulotomy than the hydrophobic acrylic IOL despite its round edge.

The authors observed that these results were in line with those in their 5-year follow-up study. They attributed the efficiency of the silicone IOL in inhibiting PCO in the long run to its material property. The adhesiveness of silicone to vitronectin and collagen type IV was significantly higher than the adhesiveness of acrylate to these proteins, 1 week after incubation. Silicone is believed to catalyze the process of myofibroblastic transdifferentiation and collagenous sealing of the capsular leaves at the optic edge. This might have resulted in more permanent sealing at the optic edge so that it could better withstand mechanical pressure from proliferating LECs. In conclusion, after 12 years, there was no difference in PCO or overall survival without capsulotomy between the acrylic and the silicone IOLs. The HSM PMMA IOL had a significantly higher PCO fraction than the silicone IOL and a lower overall survival than the acrylic IOL.

The PCO inhibitory property of the 3 IOL groups with a shorter follow-up of 2 to 3 years does not apply after 12 years. The PCO scores were not significantly higher with the hydrophobic acrylic IOL than with the silicone IOL. The reduced or lost efficiency of the sharp edge of the hydrophobic acrylic IOL is believed to result from late proliferation of LECs leading to an emerging Soemmerring ring in the peripheral capsular bag. This causes mechanical pressure, breaking the seal between the fused anterior and posterior capsule leaves. The capsular bend at the sharp posterior edge is reversed. This results in a delayed barrier failure. The LECs can migrate behind the posterior optic. There was a slope in the Nd:YAG-free survival curve of the hydrophobic acrylic IOL at 4 to 5 years, indicating that the Soemmerring ring was present from approximately 4 years onward as it took weeks to months for the LECs to proliferate and migrate to the visual axis. The current study has a few limitations. Due to the lengthy duration of the study, many patients were lost to follow-up. The 3 IOLs differed in material, design, and size. However, despite this, the results are interesting and worth reporting.

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Posterior Capsule Opacification Between 2 Aspheric Microincision Intraocular Lenses

The use of microincision cataract surgery (MICS) has necessitated the development of a generation of microincision IOLs that can be implanted through sub–2.0-mm incisions. It is important that these IOLs perform as well as IOLs designed for conventional incisions. Until recently, available microincision IOLs did not match the standards of conventional IOLs.

Keeping these factors in view, Nanavaty et al32 designed this study to evaluate differences in the incidence of PCO between 2 aspheric microincision hydrophilic IOLs (Acri.Smart 36A and Akreos MI-60) with a conventional single-piece hydrophobic acrylic spherical IOL (AcrySof SN60AT; Alcon Laboratories, Inc.). All eyes underwent standardized phacoemulsification for bilateral cataract performed by a single surgeon. The capsulorhexis was fashioned to overlap the IOL optic edge by 360 degrees. Either the Acri.Smart 36A (negatively aspherical IOL) or the Akreos MI-60 (aspherically neutral IOL) was injected through a 2.4-mm temporal clear corneal incision in the first eye. The AcrySof SN60AT IOL was implanted in the fellow eye within 3 weeks. All patients were examined postoperatively at 1, 3, 6, 12, and 24 months. The digital retroillumination images of each of the eyes were analyzed to measure the percentage area of PCO in the capsulorhexis area. The mean percentage PCO score was significantly less with the Acri.Smart 36A IOL when compared with the Akreos MI-60 IOL at 1, 3, and 12 months (P = 0.03, P = 0.02, and P = 0.05, respectively). Further, there was a significant difference in the percentage of PCO scores at 1 month and 12 months among all 3 IOLs (P = 0.01 and P = 0.04). At 1 month, the AcrySof SN60AT IOL showed a higher level of PCO, whereas at 12 months, the Akreos MI-60 IOL showed a higher level of PCO. It increased linearly with time for the Acri.Smart 36A IOL and the Akreos MI-60 IOL, with a maximum of up to 16% and 23%, respectively. Further, the capsulotomy rate was 4.8% (2 out of 42 eyes) with the Acri.Smart 36A IOL 24 months postoperatively. With the Akreos MI-60 IOL, the authors found a mean PCO score of 22.57% ± 25.56% at 2 years and 8 eyes (19%) required Nd:YAG capsulotomy for a visually significant PCO. At 2 years, the mean PCO score was lower than 11% for the conventional AcrySof IOL and 23% for the Akreos MI-60 IOL. With the hydrophilic acrylic microincision IOLs, PCO showed a trend toward progression over the 2-year follow-up.

Hydrophilic acrylic material and the posterior optic edge design of the IOL influence PCO performance. The Acri.Smart 36A IOL is a hydrophilic IOL with a hydrophobic surface and is used as a platform for toric, multifocal, and multifocal toric IOLs. It is likely that these variations will have a similar incidence of PCO. The Akreos MI-60 IOL has 4 haptics with a 10-degree angulation and a 360-degree square-edged design. These features are intended to prevent PCO. In the present study, high rates of YAG capsulotomy with the Akreos MI-60 IOL were found. This could have been due to the difference in material characteristics and design or the posterior optic edge profile. Sharpness of the square edges of the IOL varies with different IOLs and is dependent on the manufacturing techniques. The absence of a square-edged barrier at the optic-haptic junction of some IOLs may contribute to the migration of LECs through the optic-haptic junction. In summary, in this study, the authors found that the Acri.Smart 36A IOL had better PCO performance than the Akreos MI-60 IOL. However, at the two-year follow-up, a conventional hydrophobic acrylic IOL had better PCO performance than both microincision IOLs.

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CONCLUSIONS

At present, PCO remains the most common complication of modern cataract surgery. Posterior capsular opacification is caused by residual LECs, which are inevitably left in the bag and undergo proliferation and metaplasia. PCO is believed to be multifactorial and influenced by factors such as age or concomitant intraocular or systemic diseases, surgical technique, and IOL design. There is considerable interest in the impact of the IOL on the development of PCO since the characteristics and the designs of the IOLs play a crucial role in preventing PCO. Furthermore, differences in PCO performance between IOLs are likely to reflect their distinction in biomaterials and designs. Current strategies to prevent PCO focus on IOL design. Clinical studies have now clearly defined important parameters. The sharpness or squareness of the edge profile is of paramount importance. The square edge seems to prevent LEC migration into the central posterior capsule. It forms a pressure barrier as it is pushed against the posterior capsule, thereby increasing fibrosis of the bag in the first few weeks after surgery. This helps prevent PCO no matter which type of IOL is used. Most surgeons now aim to make the rhexis smaller than the IOL diameter. Another important design feature is that the square edge barrier should be of 360 degrees. A break in the barrier is the Achilles’ heel, where LECs can penetrate into the posterior capsule through the optic-haptic junction. The “no space, no cell” theory is known as the main mechanism preventing PCO. Although the cortex is completely removed, the LECs at the equator could proliferate and migrate toward the posterior capsule when a potential space exists between the capsular bag and the IOL. It is generally believed that delayed or incomplete capsule-IOL interaction might increase LEC proliferation and migration due to weak adhesion. Two key factors should be considered: capsular bend formation and posterior capsule apposition with the IOL. Early and rapid formation of the capsular bend could block LEC migration and proliferation. Tight adhesion between the posterior capsular bag and the IOL could create a second defensive barrier to inhibit LEC migration and proliferation. Many clinical studies have also shown that PCO rates seem to be higher with hydrophilic IOLs in comparison with hydrophobic IOL materials. This is related to an intrinsic property of the hydrophilic material. There is a large amount of experimental works on destroying LECs at the time of surgery by drug delivery, surgical technique, or physical LEC destruction, but none of these has been applied in clinical practice lest there be of pharmacological bystander damage elsewhere in the eye or the risk of increased surgical complications, time or cost. Present research now focuses on modulating LECs rather than destroying them. Last but not least implantation of IOLs with improved designs and enhanced surgical techniques have reduced the incidence of PCO.

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Keywords:

phacoemulsification; posterior capsule opacification; intraocular lens; neodymium:yttrium-aluminum-garnet laser capsulotomy

© 2014 by Asia Pacific Academy of Ophthalmology