Dr. Samaresh, S13187, Dr. Vaishali Abhaykumar Vasavada, Dr. Viraj Abhayakuma Vasavada, Dr. Shail
Introduction
Posterior capsule opacification (PCO) is the most common complication followingcataract surgery and is generally treated with Nd:YAG laser capsulotomy. Several factors play a role in the formation of posterior capsule opacification (PCO) such as variations in surgical technique, patient characteristics, lens design, design of the edge of the lens and lens material used.8-10A complete 360-degree cover of the anterior capsulorhexis over the intraocular lens (IOL) optic also influences PCO development.11-14
Several clinical and experimental studies have been performed to demonstrate the role played by IOL materials and designs inreducing the incidence of PCO.Both hydrophilic and hydrophobic IOLs have been commonly used in cataract surgeries. Hydrophobic acrylic IOLs are generally associated with lowPCOrates. However, it is uncertain whetherthis finding can be attributed to differences in the type of materialof the lensesor to variations in the optic edge design. Of the two IOL types, it is uncertain whether hydrophilic or hydrophobic IOLs are better for PCO prevention.In our previous study,whenwe compared posterior capsule opacification in contralateral eyes with single-piece hydrophobic acrylic IOLs (AcrySof SN60WF)against 2 single-piece hydrophilic acrylic IOLs with different configurations (hydrophilic C-flex 570C or Rayner or Akreos Adapt IOLs) 3 years postoperatively, we found that PCO wassignificantly less with AcrySof hydrophobic acrylic IOLs.21 The development of PCO is indisputably a dynamic process and a follow-up over a long-term duration is correlated with a high incidence of PCO.There is very little data available on PCO development over a long-term duration. Using the same cohort,we decided to compare the degree of PCO development on along-term basisin contralateral eyes 5 years aftercataract surgery.
Material and Methods:
Patients with uncomplicated age-related cataract, who were otherwise healthy, were included in the study. The exclusion criteria were as follows: patients with a history of diabetes mellitus, glaucoma, high myopia (axial length > 27.0 mm), pseudoexfoliation, traumatic cataract, subluxated cataract, previous ocular surgeries and allergy to dilating drops. All the patients underwent a thorough slit lamp examination including intraocular pressure assessment. The fundus was examined using direct and indirect ophthalmoscopy.
The patients were randomly assigned to one of two groups. In both groups, one of the eyes received a single-piece hydrophobic acrylic intraocular lens and the other eye received a hydrophilic acrylic intraocular lens with different configurations. In Group 1, one eye of the patient received an AcrySof SN60WF IOL (hydrophobic group)and the contralateral eye of the same patient received an Akreos Adapt IOL [Group 1: AcrySof IQ SN60WF IOLversus Akreos Adapt IOL (n= 35 patients)]. In Group 2, one eye of the patient received an AcrySof IOL (hydrophobic group) and the fellow eye received a Rayner C-flex IOL[Group 2: AcrySof IQ SN60WF IOLversusC-flex 570C Rayner IOL (n=33 patients)].
Intraocular Lenses
The 3 IOLs differed in material, design,and posterior edge configuration at the optic-hapticjunction.The single-piece hydrophobic acrylic IOL (AcrySof IQSN60WF, Alcon Laboratories, Inc.) (hydrophobic group)has an optic diameter of 6.00 mm and an overall length of13.00 mm. The optic has a sharp posterior square edge excludingthe haptic–optic junction. The haptics have a modifiedL-type design. The optic is biconvex with asphericity on the posterior surface.One of the single-piece hydrophilic acrylic IOLs (C-flex570C, Rayner Intraocular Lenses, Ltd.) has an optic diameter of 5.75 mm and an overall length of12.00 mm. The optic has a 360-degree raised ridge encirclingthe periphery of the anterior and posterior surfaces of theoptic body, including the optic-hapticjunction. The opticsand haptics are made of a 2-hydroxyethyl (methacrylate/methyl methacrylate) copolymer.The other single-piece hydrophilic acrylic IOL (AkreosAdapt, Bausch & Lomb) has an opticdiameter of 6.00 mm and an overall length of 10.50 mm to11.00 mm. It has 4 fixation points (haptics) with a 360-degreedouble-squared edge. It is made of a polyhydroxyl(ethylmethacrylate/methyl methacrylate) copolymer.
Randomization
Based on the sample size estimated for the study, a computer-generated randomization plan was used for the firsteye undergoingsurgery. The assignment options were as follows:a hydrophobic IOL in the first eye and a hydrophilic IOL (Akreos) in the secondeye; a hydrophobic IOL in the first eye and a hydrophilic IOL(C-Rayner) in the second eye; a hydrophilic IOL (Akreos) in the first eye and a hydrophobicIOL in the second eye; a hydrophilic IOL (C-Rayner) in the first eyeand a hydrophobic IOL in the second eye. The assigned IOL wasrevealed to the surgeon by the circulating nurse just beforeIOL implantation in the first eye of every patient undergoingphacoemulsification.The contra-lateral eye had phacoemulsificationand implantation of the other IOL within 3 months
Follow-up Examination and Image Acquisition:
The patients were asked to return for postoperative follow-up visits at 1 month, 1, 3, and 5 years. Digital retroillumination photographic documentation was performed at all the follow-up visits, after maximal pupil mydriasis, at a fixed illumination and magnification. We used a digital camera (Nikon) mounted on a slit lamp (Haag-Streit USA) with an external light and flash light source, which provided coaxial illumination from the flash pack through a fiber optic cable attached to the camera.Thereafter, at every follow-up visit, photo documentation of the posterior capsule was performed on a widely dilated pupil using retroillumination. The images of the posterior capsules of each patient taken at every follow-up visit were saved in a separate folder. These images provided information onthe onset and progression of PCO. The eye had total cover if the capsulorhexisrim completely overlapped the anterior surface of the IOL optic for 12 clock hours.If the overlap was between 1 to 10 clock hours, the eye had partial cover.
Posterior Capsule Opacification Image Interpretation and Analysis:
All the digital images were analyzed for PCO using the Evaluation of Posterior Capsule Opacification 2000 (EPCO) program.(A software program developed by Manfred Tetz and Christophe Nimsgern, Universitats-Augenklinik Charite, Berlin, Germany). Posterior capsule opacification was evaluated for the entire IOL optic (within the capsulorhexis margin) and for the central 3 mm optic zone. The boundaries and each opaque area of the posterior capsule were drawn on the stored images using a computer mouse so that afraction of the opaque area could be calculated using the Evaluation of Posterior Capsule Opacification software. Evaluation of Posterior Capsule Opacification program providesa morphological assessment of PCO, in which the geographical extent and density of backscatter on retroilluminated images determine the overall score. The density of opacification was clinically graded as 0 (none), 1 (minimal), 2 (mild), 3 (moderate) or 4 (severe). Individual PCO values for each image were calculated by multiplying the density of opacification by the fraction of the capsular area involved behind the IOL optics (within the capsulorhexis margin) and the central 3 mm optic zone. The value was interpreted in terms of Evaluation of Posterior Capsule Opacificationscore and area. Evaluation of Posterior Capsule Opacificationscore (PCO density x area)was expressed on a scale of 0 to 4. Evaluation of Posterior Capsule Opacificationarea (mm2) was rated between 0% and 100%.
Observations:
The primary observations included an assessment of the overall development of PCO at different time points. All these observations were made within the capsulorhexis margin and also within the central 3 mm area of the optic. We also assessed the impact of the anterior capsule relationship on the IOL optic at different time points. Neodymium yttrium-aluminum-garnet capsulotomy rates were also assessed.
Sample Size Calculation:
A pilot study of the baseline EPCO scores was performed.The mean EPCO score at baseline was 4.3 ± 6.5 inthe hydrophobic group, 4.8 ± 3.8 in hydrophilic group C (Rayner IOLs),and 10.9 ± 13 in hydrophilic group A (Akreos Adapt IOLs). In a previous studyof 53 contralateral eyes,the PCO area at 1 year was 4.9%with the previous generation of hydrophobic acrylic IOLs and 50.3% with hydrophilic acrylic IOLs. Based onthe expectation that the newer IOL models would reducethis difference, a change at 3 years of 7%, 13% and 10% respectivelywas assumed. To detect this change in PCO witha 1-sided level of 5% and a power of 80% (1-b), a samplesize of 30 eyes for the 2:1 design was found to be adequate.Sincethis was a contralateral study, a sample of 120eyes of 60 patients was chosen. To account for dropouts, 76patients were recruited for bilateral surgery.
Results:
There was no significant difference in the mean age when compared between the 2 groups. (Group1 Vs Group 2:60.6±8.6 Vs 59.7±7.6 years.P=0.78, Mann-Whitney Test). There was no significant difference in mean follow up in 2 groups. Group 1:AcrySof IQ SN60WF IOLs Versus Akreos Adapt IOLs: 1815.5± 58.1 Vs 1844.7±84.6 days. P=0.22.Group 2:AcrySof IQ SN60WF IOLs Versus C-flex 570C Rayner IOLs:1850.8 ±60.8 Vs 1830.1± 47.9 days P=0.25, Independent sample T test).
Mean EPCO Score and EPCO Area Values Within the Capsulorhexis Margin and the Central 3.0 mm Optic Area:
Group 1: AcrySof IQ SN60WF IOLsVersusAkreos Adapt IOLS
Within the Capsulorhexis Margin
Both groups had comparable values at the baseline examination (EPCO Score &Area: P=Not Significant). When we compared the EPCO score and area within the capsulorhexis margin at 1,2, 3 and 5 years postoperatively, there was a significant decrease in PCO score and area with AcrySof IOLs when compared withAkreos Adapt IOLs (Group 1: EPCO Score: 1 year: P<0.001, 2 years: P<0.001, 3 years: P<0.001,5years: P<0.001;EPCO Area: 1 year: P<0.001,2 years: P<0.001,3 years: P<0.001,5years: P<0.001).(Figure 1).
Central 3.0 mm Optic Area
When EPCO was compared within the central 3 mm opticat baseline and1 year, there was no significant difference in PCO between the 2 IOLs(P=Not Significant). However, there was a significant decrease in EPCO score and areawith AcrySof IOLswhen compared withAkreos Adapt IOLs at the 2, 3 and 5 years follow-up(EPCO Score – 2 years: P<0.01,3 years: P<0.01,5years: P<0.001;EPCO Area – 2 years: P<0.001,3 years: P<0.001,5years: P<0.001).
Group 2: AcrySof IQ SN60WF IOLs VersusC-flex 570C Rayner IOLS
Within the Capsulorhexis Margin
Both groups had comparable values at the baseline examination(EPCO Score & Area: P=Not Significant). When we compared the EPCO score and area within the capsulorhexis margin at 1, 2,3 and 5 years postoperatively, there was a significant decrease in PCO score and area with AcrySof IOLs when compared withRayner IOLs (EPCO Score – 1 year: P<0.001,2 years: P<0.001,3 years: P<0.01,5years: P<0.04;EPCO Area: 1 year: P<0.001,2 years: P<0.001,3 years: P<0.001,5years: P<0.001) at every time frame. (Figure 2)
Central 3.0 mm Optic Area:
At baseline,1 and 2 years, there was no significant difference in the EPCO score and area between the 2 IOLs(P=Not significant).On the other hand, there was a significant decrease in EPCO score and areawith AcrySof IOLs at 3 and 5 yearswhen comparedwithRayner IOLs(EPCO Score – 3 years: P<0.01, 5years – P<0.04;EPCO Area –3 years: P<0.02, 5years – P<0.001).
A Comparison of Evaluation of Posterior Capsule Opacification Score and Area with Anterior Capsule Relationship:
Total On:
Group 1:AcrySof IQ SN60WFIOLs Versus Akreos Adapt IOLs
Within the Capsulorhexis Margin
Both groups had comparable values at the baseline examination (EPCO Score and Area – P=Not Significant).When we compared the EPCO score and area within the capsulorhexis margin at 1, 2,3 and 5 years postoperatively, there was a significant decrease in PCO score and area with AcrySof IOLS when compared withAkreos Adapt IOLs (EPCO Score – 1 year: P<0.001,2 years:P<0.001,3 years: P<0.001,5years: P<0.001;EPCO Area –1 year: P<0.001,2 years: P<0.001,3 years: P<0.001,5years: P<0.001) at every time frame.
Group 2: AcrySof IQ SN60WFIOLs VersusC-flex 570C Rayner IOLS
Within the Capsulorhexis Margin
Both groups had comparable values at the baseline examination (EPCO Score and Area – P=Not Significant). When we compared the EPCO score and area within the capsulorhexis margin at 1, 2,3 and 5 years postoperatively, there was a significant decrease in PCO score and area with AcrySof IOLs when compared with Akreos Adapt IOLs (EPCO Score – 1 year: P<0.001,2 years: P<0.001,3 years: P<0.001,5years: P<0.001; EPCO Area – 1 year: P<0.001, 2 years: P<0.01,3 years: P<0.002,5years: P<0.05) at every time frame.
At the 5 years follow-up,8 eyes of 35 patients in the Akreos group and 4 eyes of 33 patients in the Rayner group required an Nd: YAG capsulotomy. However,only in 1 eye in the AcrySof group required an Nd: YAG capsulotomy at the 5 years follow-up. Of the 8 eyes in Akreos group 5 eyes had to undergo Nd: YAG capsulotomy within 3 years while another 3 eyes between 3 to 5 years respectively. Of the 4 eyes in Rayner group 2 eyeshad to undergo Nd: YAG capsulotomy within 3 years while another 2 eyes between 3 to 5 years respectively.
Discussion:
In the present study, we found significantly lower level ofPCO in the hydrophobic acrylic IOL group when compared with the hydrophilic acrylic IOL group at every follow-up even upto 5 years after surgery. Withhydrophobic IOLs, an increase in PCO was observed up to 3 years and PCO stabilized between 3 to 5 years. It is well-known that the bulky haptics of the single-piece AcrySof® IOLs extend directly from the posterior optic surface, leaving a section of the circumference of the optic without a sharp edgecausing a loss of barrier function to migrating lens epithelial cells.22-25In the present study, we found a gradual increase in the development of PCO in the AcrySofgroup up to 3 years which stabilized at 5 years. A similar observation was made while evaluating long-term PCO with single-piece AcrySofSN60AT IOLs at the 5 years follow-up.16We believe that early PCO formation can be attributed to deficiencies in the fusion process of the capsule. This can cause delayed or incomplete capsular bend formation at the posterior optic edge. This, in turn, allows lens epithelial cells to migrate behind the IOL optic. In the long-term,theexisting migratory lens epithelial cells at the optic-haptic junction or beneath the IOL optic create a tight barrier effect against the posterior capsule preventing the migration of lens epithelial cells towards the central visual axis. We also believe that, at times, despite fibrotic changes on the anterior capsule, the single-piece IOL does not yield to any changes due to its stable design platform. This maintains the sealing effect and prevents the migration of lens epithelial cells.
In the present study, we found significantly less PCO in hydrophobic acrylic IOLs when compared with hydrophilic acrylic IOLs. This is in accordance with the results of earlier studies with shorter follow-up durations.17,18,26,27A metanalysis was conductedof all randomized clinical trials evaluating postoperative PCO results and the rate of Nd:YAG laser capsulotomy at the2year follow-up between hydrophilic acrylic and hydrophobic acrylic IOLs.26 Based on the analysis, authors concluded that hydrophobic acrylic IOLs led to significantly less PCO at the1-year and 2-year follow-up periods. Further reduced rates of Nd:YAG laser capsulotomy were observed following hydrophobic acrylic IOL implantation 2years aftercataract surgery.In another retrospective study,28the authors evaluated posterior capsule opacification rates in three different intraocular lenses -AcrySof SN60AT IOLs, Akreos Adapt IOLs and Tecnis Acryl IOLswitha mean follow-up of 41.5 months. They observedthat the risk of PCO development and Nd:YAG capsulotomy was significantly higher withhydrophilic Akreos IOLs when compared with both AcrySof and Tecnis hydrophobic IOLs.The acrylic hydrophobic material has an adhesive surface that results in greater IOL optic-capsule adhesion and more rapid capsular bend formation. This creates a shrink-wrap effect wherein the posterior lens capsule is tightly fitted against the back of the IOL optic.29-31 Linnola et al. proposed a bioactive-based explanation, known as the sandwich theory and also demonstrated the strong binding of fibronectin and laminin to acrylic hydrophobic IOLs (AcrySof).32,33
In the present study, unlike the square edge of hydrophobic IOLs, the hydrophilic modelshave a 360-degree enhanced square edge of the optic, which includes the optic-haptic junction. However, despite this lens design of hydrophilic models, the IOLsdid not provide a barrier effect for migrating lens epithelial cells from 2 years even up to 5 years respectively.A reasonable interpretation for the difference could be that hydrophobic acrylic aspheric IOLshavea symmetric biconvex configuration. The posterior surface of the aspheric IOL is more convex than that of the relatively flat spherical IOLs.34,35In theory, the decrease in the convexity of the posterior spherical IOL surface reduces the potential for contact between the IOL and the posterior capsule more than the highlyconvex aspheric IOL.34,35 Using scanning election microscopy, in experimental trials it was observedthat aspheric IOLs had the thinnest edge of all hydrophobic IOLs. On the other hand, experimental studies were conducted to evaluate and definethe sharpness of the microedge structure of intraocular lenses for commercially available square-edged hydrophilic IOLsusing the SEM technique.36-38Based on this analysis, it was concludedthat hydrophilic acrylic IOLshada large variation of the deviation area from a perfect square. They suggested that this deviation is probably due to the manufacturing process of hydrophilic acrylic lenses, which involvesa lathe cut from dehydrated blocks, which are then rehydrated. Water absorption by the IOL material may render the final aspect of the edge rounder as the IOL swells. We believe shrink wrapping of the IOL by the capsular bag, which enhances contact between the posterior IOL surface and the posterior capsule,could be the factor that may play the most important clinical role in evening out the differences in the microedge profiles observed in the above-mentioned studies.
In the present study, there was a significant decrease in PCO with “total on” anterior capsule cover on the entire IOL optic with AcrySof IOls when compared against the other 2 hydrophilic IOLs at every time frame. We did not perform a subgroup comparison of the scores between eyes with complete overlap of the anterior capsulorhexis on the IOL optic edge versus eyes with partial overlap because there were few cases of partial cover. There is supporting evidence in literature that the incidence and severity of PCO is strongly affected by, and may be proportionate to, the degree of anterior capsule overlap on the IOL.11-14 The results obtained by placing the edge of the anterior capsule completely over the IOL optic suggest that the lens implant, which is sequestered in the capsular bag, is pushed in a posterior direction due to pressure from the anterior capsule. This force may lead to greater contact between the IOL and the posterior capsule, thereby creating an effective barrier for migrating lens epithelial cells.
In the present study, the low rate of PCO formation in the hydrophobic IOL could possibly be attributed to the large size of the IOL. In a few studies, a low incidence of PCO was observed when large acrylic IOLs of 6.0 mm were used.39,40 In the present study, upto the 5 years follow-up, the Nd:YAG capsulotomy rate was significantly more with hydrophilic IOLs when compared withhydrophobic IOLs. In a retrospective, longitudinal cohort study over a 5-year period, the authors observed that the hydrophobic acrylic IOL material and the square posterior optic edge (AR40, AR40e (Abbott Medical Optics, Santa Ana, California) were associated with significantly lower ratesof capsulotomies, compared with hydrophilic IOLs (BL27 (Bausch & Lomb, Rochester, New York).41
In the present study, the difference in the PCO values between the 3 IOLs can be explained by their configuration, that is, the optic size, the edge design and the haptic design. Further the results of our study should not be directly compared with other reports. Firstly, the SN60WF IOL has thin optic edges and haptics, which would help in the adhesion of the anterior and posterior capsules, thereby preventing lens epithelial cell migration. Secondly, different methodologies of evaluating PCO may result in different study outcomes,which should be clarified in future studies. Thirdly, we evaluated 6.0 mm optic IOLs. There arevery few studies that evaluated 6.0 mm optic IOLs. Using a single surgeon, standardized surgical techniques, and a prospective clinical study design removes the influence of surgical factors and indicates that the development of PCO is, in all likelihood, due to IOL-related factors.
On comparing 3 different models of single-piece acrylic IOLsof different materials, optic designs and haptic configurations, we concluded that the PCO values of all 3 IOLs were comparable at baseline. Hydrophobic acrylic IOLs with aspheric optics had lower PCO values 5 years postoperatively as compared to the 2 single-piece hydrophilic IOLs. A low incidence of PCO was observed in eyes with anterior capsule cover on the IOL optic with single-piece hydrophobic acrylic IOLS.
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