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Posterior capsule opacification and lens epithelial cell layer formation: Hydroview hydrogel versus AcrySof acrylic intraocular lenses
Posterior capsule opacification and lens epithelial cell layer formation: Hydroview hydrogel versus AcrySof acrylic intraocular lenses Antony Scaramuzza, MB, BS (Hons 1), Glen T. Fernando, MB, BS (Hons 1), Basil B. Crayford, MMed, FRACO ABSTRACT Purpose: To quantitatively compare the incidence of visually significant posterior capsule opacification (PCO) and lens epithelial cell (LEC) layer formation on the anterior surface of Hydroview姞 hydrogel and AcrySof姞 acrylic foldable intraocular lenses (IOLs) after implantation. Setting: Single-surgeon ophthalmology practice, Orange Base Hospital, and Dudley Private Hospital, Orange, New South Wales, Australia. Methods: This retrospective study comprised 166 eyes of 150 patients (after exclusions) who had cataract extraction and insertion of a foldable IOL in the capsular bag by a single surgeon using a standardized phacoemulsification technique from December 1997 to September 1998. The mean follow-up was 13.1 months (range 6.0 to 23.6 months). The eyes were divided into 2 groups based on the type of IOL implanted: Storz Hydroview H60M (81 eyes) or Alcon AcrySof MA30BA (85 eyes). A neodymium:YAG posterior capsule laser capsulotomy (PC YAG) was performed for an objective decrease in Snellen best corrected visual acuity (BCVA) of more than 1 line, significant visual symptoms, or both. This was used as a measure of visually significant PCO. An Nd:YAG anterior surface clearance (ASC YAG) was done for LEC layer formation anterior to the IOL to better visualize or facilitate treatment of PCO. The rates of PC YAG and ASC YAG after Hydroview and AcrySof IOL implantation were statistically compared. Results: Forty-five eyes (55.6%) in the Hydroview IOL group and 3 eyes (3.5%) in the AcrySof IOL group required a PC YAG; the risk difference was 52.0% (P ⬍ .001). An ASC YAG was required in 27 eyes (33.3%) in the Hydroview group and 1 eye (1.2%) in the AcrySof group; the risk difference was 32.2% (P ⬍ .001). Survival analysis demonstrated that the only independent predictor of the incidence of PC YAG and ASC YAG over time was IOL type, with the Hydroview IOL group having a statistically significantly higher incidence of both procedures. Conclusion: There was a greater incidence of visually significant PCO and LEC layer formation on the anterior surface of Hydroview IOLs than of AcrySof IOLs. J Cataract Refract Surg 2001; 27:1047–1054 © 2001 ASCRS and ESCRS
© 2001 ASCRS and ESCRS Published by Elsevier Science Inc.
0886-3350/01/$–see front matter PII S0886-3350(01)00829-4
INCREASED PCO AND LECS WITH HYDROVIEW IOLS
P
osterior capsule opacification (PCO) continues to be a major complication of modern cataract surgery with intraocular lens (IOL) implantation. It has significant associated social and economic consequences. A 1998 metaanalysis1 found that visually significant PCO develops in 11.8% of patients by 1 year after cataract surgery and posterior chamber IOL (PC IOL) implantation (phacoemulsification or extracapsular cataract extraction [ECCE] with various IOL models), rising to 28.4% at 5 years postoperatively. Posterior capsule opacification develops from residual lens epithelial cells (LECs) that undergo proliferation, migration, metaplasia, and opacification2,3 in the capsular bag after cataract extraction. The pathogenesis of this process has not been fully elucidated, and there is much encouraging research on the pathophysiology and molecular biology of LECs.4 Posterior capsule opacification can result in significant visual symptoms including decreased visual acuity, impaired contrast sensitivity, and increased glare.5,6 Mechanical traction from PCO can also cause IOL malpositioning.2 Several factors have been identified as being potentially important in the development of PCO. These include concomitant ocular pathology,7 surgical technique and thorough cortical cleanup,8,9 and IOL material,10,11 design,12–17 and placement.18 The treatment of PCO by neodymium:YAG (Nd: YAG) laser capsulotomy is effective and relatively easy. There are, however, several serious complications including cystoid macular edema, retinal detachment, and a postprocedure increase in intraocular pressure.19 –23 Intraocular lens damage and decentration can also occur.20,24 –26 These potentially sight-threatening complications, as well as the financial cost of large numbers of Nd:YAG laser capsulotomies, must be considered. Furthermore, modern ECCE can be used worldwide only when PCO has been minimized given the poor access to laser capsulotomy in developing countries. Accepted for publication October 25, 2000. From a single-surgeon ophthalmology practice, Orange Base Hospital, and Dudley Private Hospital, Orange, New South Wales, Australia. None of the authors has a financial or proprietary interest in any material or method mentioned. Reprint requests to Dr. Basil B. Crayford, Dudley Specialist Medical Centre, 271 March Street, Orange, 2800, New South Wales, Australia. E-mail: [email protected]. 1048
Lens epithelial cell layer formation on the anterior IOL surface has been described and is believed to result from LEC proliferation and migration from the anterior capsule beyond the capsulorhexis margin.27–30 Koch and coauthors31 recently studied surgically excised samples of this membrane with the scanning electron microscope and found it to be multilayered and consisting of LECs that had differentiated into fibroblast-like cells with associated extracellular matrix, fibrinous collagen, and basal lamina-like material. An LEC layer anterior to the IOL can result in visual symptoms and has been successfully treated with the Nd:YAG laser.31 Higher-than-expected PCO and LEC layer formation rates were noted in more patients receiving a Hydroview威 hydrogel IOL (model H60M, Storz) than in those receiving an AcrySof威 acrylic lens (model MA30BA, Alcon) implanted by the same surgeon using the same technique at the same institutions over the same period. Thus, this study was undertaken to compare PCO formation with the Hydroview and AcrySof IOL using the rate of Nd:YAG posterior capsule laser capsulotomies (PC YAG). In addition, the presence of LEC layer formation on the anterior surface of the IOL was compared using the rate of Nd:YAG laser anterior surface clearance (ASC YAG). The surgeon (B.C.) ultimately stopped implanting the Hydroview H60M, not only because of these issues but also because of visually significant calcification of the IOL optic.32
Patients and Methods This retrospective study comprised 289 consecutive eyes of 246 patients who had cataract extraction and IOL implantation in the capsular bag from December 1997 to September 1998. The surgery was performed by a single experienced surgeon (B.C.) using the same technique at 2 hospitals in the same town. A retrobulbar block was used routinely except in patients on warfarin, who received topical or general anesthesia. Preoperative mydriasis was achieved with topical tropicamide 1%, phenylephrine 10%, and cyclopentolate 1%. A 2.6 mm stepped temporal clear corneal section was made followed by a continuous curvilinear capsulorhexis (CCC) slightly smaller than the IOL optic diameter using a 25 gauge cystotome and forceps. Hy-
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drodissection with intraocular balanced salt solution (BSS威) was performed. In-the-bag phacoemulsification was by the divide-and-conquer technique using the Storz Millennium威 or Alcon Universal威 unit. Combined irrigation/aspiration was then performed for thorough cortical removal before routine posterior capsule polishing. The corneal section was subsequently widened using a 4.0 mm keratome. Sodium hyaluronate 1.6% (Amvisc Plus威) or sodium hyaluronate 3.0%– chondroitin sulfate 4.0% (Viscoat威) was used and later removed. A foldable PC IOL was placed in the capsular bag. Miosis was induced intraoperatively with acetylcholine chloride 1% (Miochol威). The section was not sutured routinely. Subconjunctival betamethasone acetate, betamethasone sodium phosphate (Celestone Chronodose威), and gentamicin were used in all cases. The eye was then irrigated with half-strength povidone– iodine (Betadine威) and BSS. Postoperatively, patients received a single oral dose of acetazolamide (Diamox威) followed by topical gentamicin sulfate (Genoptic威) and dexamethasone (Maxidex威) eyedrops tapered over 3 weeks. Patients were evaluated 1 day, 1 week, and 1 and 6 months postoperatively. Those with symptoms or another cause for follow-up were seen as needed. The medical records of each patient were reviewed and the following data recorded: sex, date of birth, date of surgery, affected eye, hospital at which surgery was performed, IOL type, IOL power, preoperative and postoperative Snellen best corrected visual acuities (BCVAs), PC YAG date and energy, ASC YAG date and energy, BCVA before and after Nd:YAG, date last seen, surgical complications, and coexisting ocular pathology. Exclusion criteria included a surgical complication, ECCE other than phacoemulsification, scleral section, traumatic or congenital cataract, combined phacotrabeculectomy, previous retinal laser treatment, retinopathy or maculopathy, diabetic retinopathy (greater than nonproliferative), late glaucoma expected to affect visual acuity, corneal disease or previous penetrating keratoplasty, and implantation of an IOL other than a Hydroview H60M or AcrySof MA30BA. Patients with a follow-up of fewer than 6 months were also excluded. The remaining 166 eyes of 150 patients were divided into 2 groups based on the type of IOL implanted: Hydroview H60M (81 eyes of 76 patients) or Alcon AcrySof MA30BA (85 eyes of 79 patients). A subgroup
of 5 patients had a Hydroview IOL implanted in 1 eye and an AcrySof IOL in the fellow eye during the study. The Hydroview H60M IOL consists of a foldable 6.0 mm diameter equiconvex hydrogel copolymer (2hydroxyhexyl methacrylate/6-hydroxyethyl methacrylate) optic linked by an interpenetrating polymer network to modified C-loop poly(methyl methacrylate) (PMMA) haptics with an overall diameter of 12.5 mm. It is hydrophilic (18% water by weight in vivo). The AcrySof MA30BA IOL consists of a foldable 5.5 mm diameter square-edged biconcave copolymer (2-phenylethyl acrylate/2-phenylethyl methacrylate) optic attached to angulated (5 degrees) modified C-loop PMMA haptics with an overall diameter of 12.5 mm. The AcrySof IOL is hydrophobic. A PC YAG was performed for an objective decrease in BCVA by more than 1 line as documented by a clinical assistant and for subjective visual complaints including haze, glare, and visual difficulty in low-lighting conditions where PCO was found to be the cause by dilated fundoscopy. The decision to perform a PC YAG was made by the operating surgeon in all cases. As all patients were followed in the surgeon’s private rooms, they all had equal access to laser facilities. An Alcon Nd:YAG laser (model 3000LE) was used, and the total energy (millijoules), number of pulses, and energy per pulse were recorded. Mydriasis was achieved with topical tropicamide 1% (Mydriacyl威) and phenylephrine 10%. Apraclonidine hydrochloride (Iopidine威) was instilled as a single dose, and topical fluorometholone 0.1% (FML威) was used 3 times daily for 1 week after the Nd:YAG procedure. Patients were reviewed routinely 2 weeks after the PC YAG procedure, at which time BCVA and the adequacy of the capsulotomy were assessed. An ASC YAG for an LEC layer on the anterior IOL surface was done in cases in which a PC YAG was not possible because of poor visualization of the PCO or to facilitate a PC YAG. The total energy (millijoules), number of pulses, and energy per pulse were recorded. Statistical analysis of the data was performed using Stata威 software (version 6.0, StataCorp). Snellen visual acuities were converted to decimals. The initial characteristics of the Hydroview IOL and AcrySof IOL groups were compared to test for selection bias. This included calculating the mean and standard deviation (SD) for age, length of follow-up, preoperative and postoperative
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BCVAs, and power of the implanted IOL in each group. The P value for the difference between the 2 groups in each variable was calculated using independent t tests. The patients’ sex and location of surgery were expressed as proportions for each IOL group, and chi-square analysis was used to calculate the P value for the difference between groups. Survival analysis techniques (Cox proportional hazards and Kaplan-Meier) were used to compare the PC YAG and ASC YAG rates between the Hydroview and AcrySof groups and to identify the factors influencing the rates. The mean and standard deviation for the time from IOL implantation to PC YAG and ASC YAG as well as Nd:YAG laser energy were calculated for each IOL group. The P value for the difference between the 2 groups in each variable was calculated using independent t tests. The difference in Snellen BCVA before and after PC YAG (with or without ASC YAG) was also calculated in each group and compared.
Results Table 1 shows the initial group characteristics. The mean patient age was 78.4 years ⫾ 7.5 (SD) in the Hydroview IOL group and 78.0 ⫾ 8.5 years in the AcrySof IOL group. The mean follow-up was 12.5 months (range 6.0 to 19.3 months) and 13.6 months (range 6.0 to 23.6 months), respectively. The between-group differences in age and follow-up were not statistically sig-
nificant. There was no statistically significant difference between groups in sex, preoperative BCVA, or postoperative BCVA. The differences in IOL power (diopters [D]) and location of initial surgery were statistically different between the 2 groups (Table 1). AcrySof IOLs were of higher power and were more frequently implanted at 1 hospital than Hydroview IOLs. A PC YAG was performed in 45 eyes (55.6%) in the Hydroview group and 3 eyes (3.5%) in the AcrySof group. This represents a risk difference of 52.0% (95% confidence interval [CI], 40.5-63.5; P ⬍ .001) (Figure 1). An ASC YAG was performed in 27 eyes (33.3%) in the Hydroview group and 1 eye (1.2%) in the AcrySof group. This represents a risk difference of 32.2% (95% CI, 21.6-42.7; P ⬍ .001) (Figure 2). Survival analysis using Cox proportional hazards demonstrated that the only independent predictor of time to PC YAG was IOL type, with the Hydroview associated with a hazard ratio of 20.0 requiring a PC YAG compared to the AcrySof group (backward-elimination and forced-entry methods) (P ⬍ .001). The Kaplan-Meier method also demonstrated that the Hydroview group had a statistically significantly greater incidence of PC YAG over time than the AcrySof group (P ⬍ .001, log rank test) (Figure 3). Statistical analysis of the incidence of ASC YAG over time in the 2 groups was limited because only 1 patient in the AcrySof group required the procedure compared to 27 in the Hydroview group. However, analysis demonstrated that this
Table 1. Initial group characteristics and P values for the differences between groups in each variable. Hydroview Group
AcrySof Group
Variable
Mean ⴞ SD
Proportion
Mean ⴞ SD
Proportion
P Value
Age (years)
78.4 ⫾ 7.5
—
78.0 ⫾ 8.5
—
.709*
Follow-up (months)
12.5 ⫾ 3.6
—
13.6 ⫾ 4.8
—
.085*
—
.380*
Preop BCVA Postop BCVA
0.51 ⫾ 0.17 0.88 ⫾ 0.22
—
0.83 ⫾ 0.29
—
.212*
20.9 ⫾ 2.0
—
22.2 ⫾ 2.3
—
.003*
Sex (male)
—
23/81
—
32/85
.206†
Hospital (Dudley Private)
—
47/81
—
64/85
.018†
IOL power (D)
—
0.48 ⫾ 0.23
BCVA ⫽ best corrected visual acuity *t test † Chi-square test
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Figure 1. (Scaramuzza) Comparison of the percentage of PC YAG
Figure 2. (Scaramuzza) Comparison of the percentage of ASC
procedures by IOL group (P ⬍ .001).
YAG procedures by IOL group (P ⬍ .001).
difference was statistically significant with regard to IOL type (P ⬍ .001, log rank test) (Figure 4). The mean interval from IOL implantation to PC YAG was 9.2 ⫾ 3.7 months in the Hydroview group and 12.3 ⫾ 6.8 months in the AcrySof group. The difference between groups was not statistically significant (P ⫽ .194, independent t test). The mean Nd:YAG laser powers required to perform the PC YAG were similar in both groups: 74.3 ⫾ 46.6 mJ, Hydroview group; 74.3 ⫾ 68.4 mJ, AcrySof group. The interval from implantation to ASC YAG was a mean of 8.7 ⫾ 3.6 months in the Hydroview group and 7 months in the 1 eye in the AcrySof group that required the procedure. The Nd:YAG laser power required to perform the ASC YAG procedure was a mean of 80.1 ⫾ 47.7 mJ in the Hydroview group and 79 mJ in the 1 eye in the AcrySof group. There was a statistically significant improvement in the Snellen BCVA after PC YAG (with or without
ASC YAG) in the Hydroview group (P ⫽ .001, paired t test) but not in the AcrySof group (P ⫽ .096, paired t test). The subgroup of 5 patients who received a Hydroview IOL in 1 eye and an AcrySof IOL in the fellow eye was not analyzed statistically because of the small number of samples. In this subgroup, 4 eyes (80%) with a Hydroview IOL and 1 eye (20%) with an AcrySof IOL required a PC YAG. An ASC YAG was performed in 2 eyes (40%) with a Hydroview IOL and 1 eye (20%) with an AcrySof IOL.
Figure 3. (Scaramuzza) Kaplan-Meier survival estimates for PC
Figure 4. (Scaramuzza) Kaplan-Meier survival estimates for ASC
YAG by IOL type (P ⬍ .001).
YAG by IOL type (P ⬍ .001).
Discussion The currently widely accepted surgical technique for preventing PCO was used in all cases in this study. Despite the use of a CCC2 with a diameter slightly smaller than the IOL optic,33 routine capsule polishing,34 and implantation of a biconvex IOL,12 all of
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which have been shown to reduce PCO rates, we still encountered PCO in our patients. There was a significantly greater increase in the incidence of PCO and anterior LEC layer formation in patients who received a Storz Hydroview H60M hydrogel IOL than in those who received an Alcon AcrySof MA30BA acrylic IOL. The increase was measured in terms of the rate of PC YAG and ASC YAG procedures performed in each group. The difference in the incidence of PCO development may be a result of differences in IOL design. Although both lenses are biconvex, the AcrySof has a square-edged optic. This edge design has been associated with a decreased PCO rate as is creates a discontinuous bend in the capsule, inhibiting LEC migration.14,35 In a comparative study, Ursell et al.10 concluded that the lower PCO rate achieved with AcrySof IOLs is more likely caused by IOL material than IOL design. Given the marked difference in PCO development between the 2 IOL groups in our study, it is likely that IOL material plays an important role. The AcrySof IOL has been shown to adhere strongly to a collagen film,36 thereby adhering to the lens capsule. This may provide a mechanical barrier to cell migration—the “no space–no cells” phenomenon.2 Menapace37 found a high rate of PCO with the taco-style Iogel威 hydrogel (polymacon/38% hydrated polyHEMA) IOL. In addition to the lack of adhesiveness to the capsular bag, Menapace postulates the increase in PCO is the result of the permeability of the hydrogel material, which allows continuous translental supply of nutrients to the epithelial cells. An IOL’s biomaterial also influences the complex proteinaceous and cellular biofilm that deposits on the surface the first day after implantation.10 This biofilm and the IOL material may determine future tissue reactions to the IOL. Hydrogel materials appear to be well tolerated in the eye.38,39 They are very biocompatible, causing minimal disruption of the blood–aqueous barrier (BAB).40,41 It has been suggested that the reduced BAB damage is associated with increased LEC proliferation, leading to anterior surface LECs and PCO.42 Koch and coauthors31 suggest that the high biocompatibility and hydrophilic nature of the Hydroview hydrogel IOL could be the cause of the high incidence of anterior LEC layer formation in these eyes. The incidence of LEC layer 1052
formation in the Hydroview IOL group in our study (33.3%) correlates well with that in Koch and coauthor’s study in which a layer developed in 33.16% of eyes with a Hydroview IOL. Potential selection bias and confounding factors between our 2 groups were minimized by using a consecutive series of patients belonging to a single surgeon (B.C.) who had no inherent bias regarding IOL type and was not expecting clinical abnormality at the time of IOL implantation. This is supported by our results, which show no statistically significant difference in the initial characteristics of the 2 groups except for hospital and IOL power. The difference in IOL power may be because the Hydroview H60M IOL has a lower A-constant than the AcrySof MA30BA IOL (118.3 and 118.9, respectively).43 Our survival analysis results, however, confirm that neither factor had a statistically significant effect on the rate of PCO development or anterior surface LEC layer formation. Although the surgeon did not expect the observed outcome when the IOLs were implanted, the higher PC YAG and ASC YAG rates in eyes with a Hydroview IOL was suspected by the surgeon during the follow-up, prompting this study. Potential weaknesses in our study include the use of a retrospective study design over a relatively short follow-up (mean 13.1 months) at a single center. However, the follow-up was longer (although not statistically significant) in the AcrySof group, favoring the Hydroview group. Medium- and long-term follow-up will be important in confirming the trends observed in these 2 groups. In our study, Nd:YAG laser capsulotomy was used as an indirect measure of PCO. Although several direct objective measures of PCO have been described, the use of capsulotomy as a proxy measure of visually significant PCO is well accepted in the absence of more sophisticated techniques.1 Furthermore, consistency was achieved in our study by using data from the patients of a single surgeon over a relatively narrow time frame. The rate of PC YAG in the AcrySof IOL group was 3.5%, which is comparable to rates observed by other authors.44 This suggests that the higher PC YAG rate in our Hydroview group was a result of the lens rather than the surgeon’s decision to use the Nd:YAG laser. Other objective measures of vision such as contrast sensitivity and glare testing could have been used. It is widely recognized that although some patients have se-
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vere objective PCO but no visual complaints, the converse is also true. It is the symptomatic group that requires a capsulotomy. Contrast sensitivity testing may be a more sensitive indicator of visual significance than Snellen acuity. Despite this, we were able to demonstrate a statistically significant improvement in Snellen BCVA after PC YAG in the Hydroview group. The improvement in Snellen BCVA in the AcrySof IOL group did not reach statistical significance, most likely because of the small number of PC YAG procedures performed in this group. In summary, the Hydroview IOL was associated with a higher rate of visually significant PCO and anterior IOL surface LEC layer formation than the AcrySof IOL. We attribute much of this difference to the nature of the hydrogel material. However, other characteristics of the Hydroview IOL, including the lack of a squareedged optic, reduced adhesiveness to the capsular bag, and high permeability, may also be involved. Further studies are required to determine the relative importance of these variables and to identify other potential confounding factors such as optic design and size, haptic quality, and the angle between haptic and optic. At the time this paper was written, approximately 417 000 Hydroview IOLs had been sold worldwide (personal communication, Laurie Curtin, Bausch & Lomb Surgical, March 3, 2000). In view of the results of our series of patients and the widespread use of this IOL, we believe that multicenter collaboration is needed to further investigate the unexpected increased rate of PCO and LEC layer formation anterior to the IOL with the Storz Hydroview H60M hydrogel IOL.
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rhexis size and posterior capsule opacification. J Cataract Refract Surg 1996; 22:98 –103 Rentsch FJ, Bauer W. Langzeitergebnisse nach Entfernung des Linsenepithels bei der extrakapsula¨ren Kataraktextraktion mit Phakoemulsifikation. In: Rochels R, Duncker G, Hartmann C, eds, 9. Kongress der Deutschsprachigen Gesellschaft fu¨r Intraokularlinsen Implantation, 1995, Kiel. Berlin, Springer, 1996; 399 – 407 Peng Q, Visessook N, Apple DJ, et al. Surgical prevention of posterior capsule opacification. Part 3: intraocular lens optic barrier effect as a second line of defense. J Cataract Refract Surg 2000; 26:198 –213 Nagata T, Minakata A, Watanabe I. Adhesiveness of AcrySof to a collagen film. J Cataract Refract Surg 1998; 24:367–370 Menapace R. Posterior capsule opacification and capsulotomy rates with taco-style hydrogel intraocular lenses. J Cataract Refract Surg 1996; 22:1318 –1330 Schauersberger J, Kruger A, Abela C, et al. Course of postoperative inflammation after implantation of 4 types of foldable intraocular lenses. J Cataract Refract Surg 1999; 25:1116 –1120 Chehade M, Elder, MJ. Intraocular lens materials and styles: a review. Aust NZ J Ophthalmol 1997; 25:255– 263 Packard RBS, Garner A, Arnott EJ. Poly-HEMA as a material for intraocular lens implantation: a preliminary report. Br J Ophthalmol 1981; 65:585–587 Barrett G, Constable IJ. Corneal endothelial loss with new intraocular lenses. Am J Ophthalmol 1984; 98:157– 165 Hollick EJ, Spalton DJ, Ursell PG. Surface cytologic features on intraocular lenses: can increased biocompatibility have disadvantages? Arch Ophthalmol 1999; 117:872– 878 Holladay JT. International Intraocular Lens & Implant Registry 2000. J Cataract Refract Surg 2000; 26:118 – 134 Hayashi H, Hayashi K, Nakao F, Hayashi F. Quantitative comparison of posterior capsule opacification after polymethylmethacrylate, silicone, and soft acrylic intraocular lens implantation. Arch Ophthalmol 1998; 116:1579 –1582
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0886-3350/01/$–see front matter PII S0886-3350(01)00829-4
INCREASED PCO AND LECS WITH HYDROVIEW IOLS
P
osterior capsule opacification (PCO) continues to be a major complication of modern cataract surgery with intraocular lens (IOL) implantation. It has significant associated social and economic consequences. A 1998 metaanalysis1 found that visually significant PCO develops in 11.8% of patients by 1 year after cataract surgery and posterior chamber IOL (PC IOL) implantation (phacoemulsification or extracapsular cataract extraction [ECCE] with various IOL models), rising to 28.4% at 5 years postoperatively. Posterior capsule opacification develops from residual lens epithelial cells (LECs) that undergo proliferation, migration, metaplasia, and opacification2,3 in the capsular bag after cataract extraction. The pathogenesis of this process has not been fully elucidated, and there is much encouraging research on the pathophysiology and molecular biology of LECs.4 Posterior capsule opacification can result in significant visual symptoms including decreased visual acuity, impaired contrast sensitivity, and increased glare.5,6 Mechanical traction from PCO can also cause IOL malpositioning.2 Several factors have been identified as being potentially important in the development of PCO. These include concomitant ocular pathology,7 surgical technique and thorough cortical cleanup,8,9 and IOL material,10,11 design,12–17 and placement.18 The treatment of PCO by neodymium:YAG (Nd: YAG) laser capsulotomy is effective and relatively easy. There are, however, several serious complications including cystoid macular edema, retinal detachment, and a postprocedure increase in intraocular pressure.19 –23 Intraocular lens damage and decentration can also occur.20,24 –26 These potentially sight-threatening complications, as well as the financial cost of large numbers of Nd:YAG laser capsulotomies, must be considered. Furthermore, modern ECCE can be used worldwide only when PCO has been minimized given the poor access to laser capsulotomy in developing countries. Accepted for publication October 25, 2000. From a single-surgeon ophthalmology practice, Orange Base Hospital, and Dudley Private Hospital, Orange, New South Wales, Australia. None of the authors has a financial or proprietary interest in any material or method mentioned. Reprint requests to Dr. Basil B. Crayford, Dudley Specialist Medical Centre, 271 March Street, Orange, 2800, New South Wales, Australia. E-mail: [email protected]. 1048
Lens epithelial cell layer formation on the anterior IOL surface has been described and is believed to result from LEC proliferation and migration from the anterior capsule beyond the capsulorhexis margin.27–30 Koch and coauthors31 recently studied surgically excised samples of this membrane with the scanning electron microscope and found it to be multilayered and consisting of LECs that had differentiated into fibroblast-like cells with associated extracellular matrix, fibrinous collagen, and basal lamina-like material. An LEC layer anterior to the IOL can result in visual symptoms and has been successfully treated with the Nd:YAG laser.31 Higher-than-expected PCO and LEC layer formation rates were noted in more patients receiving a Hydroview威 hydrogel IOL (model H60M, Storz) than in those receiving an AcrySof威 acrylic lens (model MA30BA, Alcon) implanted by the same surgeon using the same technique at the same institutions over the same period. Thus, this study was undertaken to compare PCO formation with the Hydroview and AcrySof IOL using the rate of Nd:YAG posterior capsule laser capsulotomies (PC YAG). In addition, the presence of LEC layer formation on the anterior surface of the IOL was compared using the rate of Nd:YAG laser anterior surface clearance (ASC YAG). The surgeon (B.C.) ultimately stopped implanting the Hydroview H60M, not only because of these issues but also because of visually significant calcification of the IOL optic.32
Patients and Methods This retrospective study comprised 289 consecutive eyes of 246 patients who had cataract extraction and IOL implantation in the capsular bag from December 1997 to September 1998. The surgery was performed by a single experienced surgeon (B.C.) using the same technique at 2 hospitals in the same town. A retrobulbar block was used routinely except in patients on warfarin, who received topical or general anesthesia. Preoperative mydriasis was achieved with topical tropicamide 1%, phenylephrine 10%, and cyclopentolate 1%. A 2.6 mm stepped temporal clear corneal section was made followed by a continuous curvilinear capsulorhexis (CCC) slightly smaller than the IOL optic diameter using a 25 gauge cystotome and forceps. Hy-
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drodissection with intraocular balanced salt solution (BSS威) was performed. In-the-bag phacoemulsification was by the divide-and-conquer technique using the Storz Millennium威 or Alcon Universal威 unit. Combined irrigation/aspiration was then performed for thorough cortical removal before routine posterior capsule polishing. The corneal section was subsequently widened using a 4.0 mm keratome. Sodium hyaluronate 1.6% (Amvisc Plus威) or sodium hyaluronate 3.0%– chondroitin sulfate 4.0% (Viscoat威) was used and later removed. A foldable PC IOL was placed in the capsular bag. Miosis was induced intraoperatively with acetylcholine chloride 1% (Miochol威). The section was not sutured routinely. Subconjunctival betamethasone acetate, betamethasone sodium phosphate (Celestone Chronodose威), and gentamicin were used in all cases. The eye was then irrigated with half-strength povidone– iodine (Betadine威) and BSS. Postoperatively, patients received a single oral dose of acetazolamide (Diamox威) followed by topical gentamicin sulfate (Genoptic威) and dexamethasone (Maxidex威) eyedrops tapered over 3 weeks. Patients were evaluated 1 day, 1 week, and 1 and 6 months postoperatively. Those with symptoms or another cause for follow-up were seen as needed. The medical records of each patient were reviewed and the following data recorded: sex, date of birth, date of surgery, affected eye, hospital at which surgery was performed, IOL type, IOL power, preoperative and postoperative Snellen best corrected visual acuities (BCVAs), PC YAG date and energy, ASC YAG date and energy, BCVA before and after Nd:YAG, date last seen, surgical complications, and coexisting ocular pathology. Exclusion criteria included a surgical complication, ECCE other than phacoemulsification, scleral section, traumatic or congenital cataract, combined phacotrabeculectomy, previous retinal laser treatment, retinopathy or maculopathy, diabetic retinopathy (greater than nonproliferative), late glaucoma expected to affect visual acuity, corneal disease or previous penetrating keratoplasty, and implantation of an IOL other than a Hydroview H60M or AcrySof MA30BA. Patients with a follow-up of fewer than 6 months were also excluded. The remaining 166 eyes of 150 patients were divided into 2 groups based on the type of IOL implanted: Hydroview H60M (81 eyes of 76 patients) or Alcon AcrySof MA30BA (85 eyes of 79 patients). A subgroup
of 5 patients had a Hydroview IOL implanted in 1 eye and an AcrySof IOL in the fellow eye during the study. The Hydroview H60M IOL consists of a foldable 6.0 mm diameter equiconvex hydrogel copolymer (2hydroxyhexyl methacrylate/6-hydroxyethyl methacrylate) optic linked by an interpenetrating polymer network to modified C-loop poly(methyl methacrylate) (PMMA) haptics with an overall diameter of 12.5 mm. It is hydrophilic (18% water by weight in vivo). The AcrySof MA30BA IOL consists of a foldable 5.5 mm diameter square-edged biconcave copolymer (2-phenylethyl acrylate/2-phenylethyl methacrylate) optic attached to angulated (5 degrees) modified C-loop PMMA haptics with an overall diameter of 12.5 mm. The AcrySof IOL is hydrophobic. A PC YAG was performed for an objective decrease in BCVA by more than 1 line as documented by a clinical assistant and for subjective visual complaints including haze, glare, and visual difficulty in low-lighting conditions where PCO was found to be the cause by dilated fundoscopy. The decision to perform a PC YAG was made by the operating surgeon in all cases. As all patients were followed in the surgeon’s private rooms, they all had equal access to laser facilities. An Alcon Nd:YAG laser (model 3000LE) was used, and the total energy (millijoules), number of pulses, and energy per pulse were recorded. Mydriasis was achieved with topical tropicamide 1% (Mydriacyl威) and phenylephrine 10%. Apraclonidine hydrochloride (Iopidine威) was instilled as a single dose, and topical fluorometholone 0.1% (FML威) was used 3 times daily for 1 week after the Nd:YAG procedure. Patients were reviewed routinely 2 weeks after the PC YAG procedure, at which time BCVA and the adequacy of the capsulotomy were assessed. An ASC YAG for an LEC layer on the anterior IOL surface was done in cases in which a PC YAG was not possible because of poor visualization of the PCO or to facilitate a PC YAG. The total energy (millijoules), number of pulses, and energy per pulse were recorded. Statistical analysis of the data was performed using Stata威 software (version 6.0, StataCorp). Snellen visual acuities were converted to decimals. The initial characteristics of the Hydroview IOL and AcrySof IOL groups were compared to test for selection bias. This included calculating the mean and standard deviation (SD) for age, length of follow-up, preoperative and postoperative
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BCVAs, and power of the implanted IOL in each group. The P value for the difference between the 2 groups in each variable was calculated using independent t tests. The patients’ sex and location of surgery were expressed as proportions for each IOL group, and chi-square analysis was used to calculate the P value for the difference between groups. Survival analysis techniques (Cox proportional hazards and Kaplan-Meier) were used to compare the PC YAG and ASC YAG rates between the Hydroview and AcrySof groups and to identify the factors influencing the rates. The mean and standard deviation for the time from IOL implantation to PC YAG and ASC YAG as well as Nd:YAG laser energy were calculated for each IOL group. The P value for the difference between the 2 groups in each variable was calculated using independent t tests. The difference in Snellen BCVA before and after PC YAG (with or without ASC YAG) was also calculated in each group and compared.
Results Table 1 shows the initial group characteristics. The mean patient age was 78.4 years ⫾ 7.5 (SD) in the Hydroview IOL group and 78.0 ⫾ 8.5 years in the AcrySof IOL group. The mean follow-up was 12.5 months (range 6.0 to 19.3 months) and 13.6 months (range 6.0 to 23.6 months), respectively. The between-group differences in age and follow-up were not statistically sig-
nificant. There was no statistically significant difference between groups in sex, preoperative BCVA, or postoperative BCVA. The differences in IOL power (diopters [D]) and location of initial surgery were statistically different between the 2 groups (Table 1). AcrySof IOLs were of higher power and were more frequently implanted at 1 hospital than Hydroview IOLs. A PC YAG was performed in 45 eyes (55.6%) in the Hydroview group and 3 eyes (3.5%) in the AcrySof group. This represents a risk difference of 52.0% (95% confidence interval [CI], 40.5-63.5; P ⬍ .001) (Figure 1). An ASC YAG was performed in 27 eyes (33.3%) in the Hydroview group and 1 eye (1.2%) in the AcrySof group. This represents a risk difference of 32.2% (95% CI, 21.6-42.7; P ⬍ .001) (Figure 2). Survival analysis using Cox proportional hazards demonstrated that the only independent predictor of time to PC YAG was IOL type, with the Hydroview associated with a hazard ratio of 20.0 requiring a PC YAG compared to the AcrySof group (backward-elimination and forced-entry methods) (P ⬍ .001). The Kaplan-Meier method also demonstrated that the Hydroview group had a statistically significantly greater incidence of PC YAG over time than the AcrySof group (P ⬍ .001, log rank test) (Figure 3). Statistical analysis of the incidence of ASC YAG over time in the 2 groups was limited because only 1 patient in the AcrySof group required the procedure compared to 27 in the Hydroview group. However, analysis demonstrated that this
Table 1. Initial group characteristics and P values for the differences between groups in each variable. Hydroview Group
AcrySof Group
Variable
Mean ⴞ SD
Proportion
Mean ⴞ SD
Proportion
P Value
Age (years)
78.4 ⫾ 7.5
—
78.0 ⫾ 8.5
—
.709*
Follow-up (months)
12.5 ⫾ 3.6
—
13.6 ⫾ 4.8
—
.085*
—
.380*
Preop BCVA Postop BCVA
0.51 ⫾ 0.17 0.88 ⫾ 0.22
—
0.83 ⫾ 0.29
—
.212*
20.9 ⫾ 2.0
—
22.2 ⫾ 2.3
—
.003*
Sex (male)
—
23/81
—
32/85
.206†
Hospital (Dudley Private)
—
47/81
—
64/85
.018†
IOL power (D)
—
0.48 ⫾ 0.23
BCVA ⫽ best corrected visual acuity *t test † Chi-square test
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Figure 1. (Scaramuzza) Comparison of the percentage of PC YAG
Figure 2. (Scaramuzza) Comparison of the percentage of ASC
procedures by IOL group (P ⬍ .001).
YAG procedures by IOL group (P ⬍ .001).
difference was statistically significant with regard to IOL type (P ⬍ .001, log rank test) (Figure 4). The mean interval from IOL implantation to PC YAG was 9.2 ⫾ 3.7 months in the Hydroview group and 12.3 ⫾ 6.8 months in the AcrySof group. The difference between groups was not statistically significant (P ⫽ .194, independent t test). The mean Nd:YAG laser powers required to perform the PC YAG were similar in both groups: 74.3 ⫾ 46.6 mJ, Hydroview group; 74.3 ⫾ 68.4 mJ, AcrySof group. The interval from implantation to ASC YAG was a mean of 8.7 ⫾ 3.6 months in the Hydroview group and 7 months in the 1 eye in the AcrySof group that required the procedure. The Nd:YAG laser power required to perform the ASC YAG procedure was a mean of 80.1 ⫾ 47.7 mJ in the Hydroview group and 79 mJ in the 1 eye in the AcrySof group. There was a statistically significant improvement in the Snellen BCVA after PC YAG (with or without
ASC YAG) in the Hydroview group (P ⫽ .001, paired t test) but not in the AcrySof group (P ⫽ .096, paired t test). The subgroup of 5 patients who received a Hydroview IOL in 1 eye and an AcrySof IOL in the fellow eye was not analyzed statistically because of the small number of samples. In this subgroup, 4 eyes (80%) with a Hydroview IOL and 1 eye (20%) with an AcrySof IOL required a PC YAG. An ASC YAG was performed in 2 eyes (40%) with a Hydroview IOL and 1 eye (20%) with an AcrySof IOL.
Figure 3. (Scaramuzza) Kaplan-Meier survival estimates for PC
Figure 4. (Scaramuzza) Kaplan-Meier survival estimates for ASC
YAG by IOL type (P ⬍ .001).
YAG by IOL type (P ⬍ .001).
Discussion The currently widely accepted surgical technique for preventing PCO was used in all cases in this study. Despite the use of a CCC2 with a diameter slightly smaller than the IOL optic,33 routine capsule polishing,34 and implantation of a biconvex IOL,12 all of
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which have been shown to reduce PCO rates, we still encountered PCO in our patients. There was a significantly greater increase in the incidence of PCO and anterior LEC layer formation in patients who received a Storz Hydroview H60M hydrogel IOL than in those who received an Alcon AcrySof MA30BA acrylic IOL. The increase was measured in terms of the rate of PC YAG and ASC YAG procedures performed in each group. The difference in the incidence of PCO development may be a result of differences in IOL design. Although both lenses are biconvex, the AcrySof has a square-edged optic. This edge design has been associated with a decreased PCO rate as is creates a discontinuous bend in the capsule, inhibiting LEC migration.14,35 In a comparative study, Ursell et al.10 concluded that the lower PCO rate achieved with AcrySof IOLs is more likely caused by IOL material than IOL design. Given the marked difference in PCO development between the 2 IOL groups in our study, it is likely that IOL material plays an important role. The AcrySof IOL has been shown to adhere strongly to a collagen film,36 thereby adhering to the lens capsule. This may provide a mechanical barrier to cell migration—the “no space–no cells” phenomenon.2 Menapace37 found a high rate of PCO with the taco-style Iogel威 hydrogel (polymacon/38% hydrated polyHEMA) IOL. In addition to the lack of adhesiveness to the capsular bag, Menapace postulates the increase in PCO is the result of the permeability of the hydrogel material, which allows continuous translental supply of nutrients to the epithelial cells. An IOL’s biomaterial also influences the complex proteinaceous and cellular biofilm that deposits on the surface the first day after implantation.10 This biofilm and the IOL material may determine future tissue reactions to the IOL. Hydrogel materials appear to be well tolerated in the eye.38,39 They are very biocompatible, causing minimal disruption of the blood–aqueous barrier (BAB).40,41 It has been suggested that the reduced BAB damage is associated with increased LEC proliferation, leading to anterior surface LECs and PCO.42 Koch and coauthors31 suggest that the high biocompatibility and hydrophilic nature of the Hydroview hydrogel IOL could be the cause of the high incidence of anterior LEC layer formation in these eyes. The incidence of LEC layer 1052
formation in the Hydroview IOL group in our study (33.3%) correlates well with that in Koch and coauthor’s study in which a layer developed in 33.16% of eyes with a Hydroview IOL. Potential selection bias and confounding factors between our 2 groups were minimized by using a consecutive series of patients belonging to a single surgeon (B.C.) who had no inherent bias regarding IOL type and was not expecting clinical abnormality at the time of IOL implantation. This is supported by our results, which show no statistically significant difference in the initial characteristics of the 2 groups except for hospital and IOL power. The difference in IOL power may be because the Hydroview H60M IOL has a lower A-constant than the AcrySof MA30BA IOL (118.3 and 118.9, respectively).43 Our survival analysis results, however, confirm that neither factor had a statistically significant effect on the rate of PCO development or anterior surface LEC layer formation. Although the surgeon did not expect the observed outcome when the IOLs were implanted, the higher PC YAG and ASC YAG rates in eyes with a Hydroview IOL was suspected by the surgeon during the follow-up, prompting this study. Potential weaknesses in our study include the use of a retrospective study design over a relatively short follow-up (mean 13.1 months) at a single center. However, the follow-up was longer (although not statistically significant) in the AcrySof group, favoring the Hydroview group. Medium- and long-term follow-up will be important in confirming the trends observed in these 2 groups. In our study, Nd:YAG laser capsulotomy was used as an indirect measure of PCO. Although several direct objective measures of PCO have been described, the use of capsulotomy as a proxy measure of visually significant PCO is well accepted in the absence of more sophisticated techniques.1 Furthermore, consistency was achieved in our study by using data from the patients of a single surgeon over a relatively narrow time frame. The rate of PC YAG in the AcrySof IOL group was 3.5%, which is comparable to rates observed by other authors.44 This suggests that the higher PC YAG rate in our Hydroview group was a result of the lens rather than the surgeon’s decision to use the Nd:YAG laser. Other objective measures of vision such as contrast sensitivity and glare testing could have been used. It is widely recognized that although some patients have se-
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vere objective PCO but no visual complaints, the converse is also true. It is the symptomatic group that requires a capsulotomy. Contrast sensitivity testing may be a more sensitive indicator of visual significance than Snellen acuity. Despite this, we were able to demonstrate a statistically significant improvement in Snellen BCVA after PC YAG in the Hydroview group. The improvement in Snellen BCVA in the AcrySof IOL group did not reach statistical significance, most likely because of the small number of PC YAG procedures performed in this group. In summary, the Hydroview IOL was associated with a higher rate of visually significant PCO and anterior IOL surface LEC layer formation than the AcrySof IOL. We attribute much of this difference to the nature of the hydrogel material. However, other characteristics of the Hydroview IOL, including the lack of a squareedged optic, reduced adhesiveness to the capsular bag, and high permeability, may also be involved. Further studies are required to determine the relative importance of these variables and to identify other potential confounding factors such as optic design and size, haptic quality, and the angle between haptic and optic. At the time this paper was written, approximately 417 000 Hydroview IOLs had been sold worldwide (personal communication, Laurie Curtin, Bausch & Lomb Surgical, March 3, 2000). In view of the results of our series of patients and the widespread use of this IOL, we believe that multicenter collaboration is needed to further investigate the unexpected increased rate of PCO and LEC layer formation anterior to the IOL with the Storz Hydroview H60M hydrogel IOL.
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