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Effect of intraocular lens design on neodymium:YAG laser capsttlotomy rates
Effect of intraocular lens design on neodymium:YAG laser capsul otomy rates Jay C. Erie, MD, Paul W Hardwig, MD, David 0. Hodge
ABSTRACT Purpose: To compare the effect of 2 poly(methyl methacrylate) (PMMA), 1-piece, biconvex intraocular lens (IOL) designs on the cumulative frequency of neodymium:YAG (Nd :YAG) laser posterior capsulotomy. Setting: Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota, USA. Methods: This retrospective study evaluated 369 eyes that had phacoemulsification with continuous curvilinear capsulorhexis (CCC) and IOL implantation in the capsular bag . Patients were placed in 1 of 2 groups based on the 1-piece, biconvex PMMA IOL design: large IOL, with a lens diameter of 13.50 to 13.75 mm, optic size of 6.5 mm, and 10 degree haptic angulation; small capsular IOL, with a lens diameter of 12.0 to 12.5 mm, optic size of 5.5 mm, and 2 degree haptic angulation. Results: Using Kaplan-Meier analysis, the frequency of Nd:YAG laser posterior capsulotomy 1, 2, and 3 years after cataract surgery was 1.6, 12.3, and 26.5%, respectively, in the large IOL group and 3.4, 9.5, and 23.5% , respectively, in the small capsular IOL group. The cumulative frequency of Nd:YAG laser capsulotomy was not statistically different between the 2 groups. Conclusion: After phacoemulsification and CCC, there was no significant difference in the Nd:YAG laser capsulotomy rate in eyes with a small , capsular design, 1-piece, biconvex PMMA IOL and those with a larger, angulated , 1-piece, biconvex PMMA IOL. J Cataract Refract Surg 1998; 24:1239-1242
P
osterior capsule opacification (PCO) is a common complication of cataract extraction with intraocular lens (IOL) implantation, approaching 50% in early investigations of poly(methyl methacrylate) (PMMA) 10Ls. 1-4 Studies have shown that the amount of PCO can vary considerably with the design and configura-
From the Department of Ophthalmology (Erie, Hardwig) and Section ofBiostatistics (Hodge), Mayo Clinic and Mayo Foundation, Rochester, Minnesota, USA. Reprint requests to jay C. Erie, MD, Mayo Clinic, Department of Ophthalmology, 200 First Street SW, Rochester, Minnesota 55905, USA.
tion of the PMMA IOL.4-7 Since these studies, significant modifications in PMMA IOL design have occurred as a result of new technology and the introduction of surgical techniques such as phacoemulsification and continuous curvilinear capsulorhexis (CCC). These modifications in PMMA IOL design include a change to a 1-piece, biconvex, PMMA IOL, a trend toward downsizing the total diameter to 12.0 to 12.5 mm and the optic size to 5.5 mm, and a reduction in haptic angulation to near planar. It is thought that this new generation of PMMA IOLs, designed for in-the-bag implantation after CCC, provides a better physiologic match between anatomy and IOL. Information on the possible impact of this IOL design change on the
J CATARACT REFRACT SURG-VOL 24, SEPTEMBER 1998
1239
EFFECT OF IOL DESIGN ON ND:YAG RATES
neodymium:YAG (Nd:YAG) laser posterior capsulotomy rate is limited. 8·9 We studied the effect of 2 posterior chamber PMMA IOL designs on the frequency ofNd:YAG laser capsulotomy for PCO after phacoemulsification and CCC.
Patients and Methods This retrospective study comprised 369 patients who had cataract extraction by phacoemulsification with CCC and IOL implantation in the capsular bag. The surgeries were performed by 1 of 2 surgeons (J.C.E., P.WH.) from January 1, 1990, through December 31, 1993, using a similar technique and modified retrobulbar anesthesia. After a scleral groove and shelving of the wound, a viscoelastic material was inserted into the anterior chamber and a CCC performed with a forceps. The nucleus was hydrodissected and removed by phacoemulsification and the divide and conquer technique. The remaining cortex was removed with an automated irrigation/aspiration handpiece. Mter viscoelastic material was injected into the capsular bag, the posterior chamber IOL was placed directly in the bag. The viscoelastic material was removed and the wound dosed with a running or interrupted 10-0 nylon suture. All patients received a subconjunctival injection of dexamethasone phosphate 0.1 o/o (Decadron®). Patients were excluded from the study if they had cataract extraction by means other than CCC with phacoemulsification, had an incomplete CCC with tear(s) of the anterior capsule, had additional procedures at the time of the cataract surgery, did not have the IOL placed within the capsular bag, had complications with posterior capsule rupture or vitreous loss, or received a foldable IOL. The decision to perform an Nd:YAG laser capsulotomy was based on subjective patient complaints of visual loss coupled with objective findings of significant PCO caused by posterior capsule fibrosis, Elschnig pearls, or both as seen on dilated biomicroscopy. Patients were divided into 2 groups according to the type of IOL implanted: a large IOL group with a 10 degree angulated, 6.5 mm optic, 13.50 to 13.75 mm diameter, 1-piece biconvex PMMA IOL (Storz 650 CUV or Pharmacia 720); a small capsular IOL group with a 1240
2 degree angulated, 5.5 mm optic, 12.0 to 12.5 mm diameter, 1-piece biconvex PMMA IOL (Storz 359 or Pharmacia 815). The 2 IOL types within each group were of the same design except for a small difference in lens diameter (0.25 to 0.50 mm). Both groups were age matched as it has been reported that PCO increases in younger patients. 10 The cumulative frequency ofNd:YAG laser capsulotomy was calculated using Kaplan-Meier survival analysis to eliminate the influence of different lengths of follow-up. The difference in the Nd:YAG posterior capsulotomy rate between the 2 groups was calculated using the log-rank test. Differences between the large and small capsular IOL groups with respect to sex were evaluated using the chi-square test for independence. 11
Results Table 1 shows the IOL characteristics of patients in each group. The percentage of Nd:YAG laser posterior capsulotomy using the Kaplan-Meier method 1, 2, and 3 years after cataract surgery was 1.6, 12.3, and 26.5%, respectively, in the large IOL group and 3.4, 9.5, and 23.5%, respectively, in the small capsular IOL group (Figure 1). The cumulative frequency ofNd:YAG laser capsulotomy was not statistically different between the 2 groups. Data power calculations predicted an 80% power to detect an 11 o/o difference in the 3 year Nd:YAG rate between the 2 groups. There was no significant difference between sexes.
Table 1. Patient characteristics. Group Large IOL
SmaiiiOL
198
171
80
77
118
94
Mean
66 :±: 15
67 :±: 13
Range
17-93
16-93
Mean
41
31
Range
6-77
6-64
Characteristic Number of patients Sex Male Female Age (years)
Follow-up (months)
J CATARACT REFRACT SURG--VOL 24, SEPTEMBER 1998
EFFECT OF IOL DESIGN ON ND:YAG RATES 100
~ ~
---- Small "capsular" IOL -
80
LargeiOL
c:
CD :I
C"
g CD
> ~ :; E :I
(.')
60 40 20
0
2
0
3
Years Figure 1. (Erie) Cumulative frequency of Nd:YAG laser capsulotomy after cataract surgery.
Discussion Advances in cataract surgery techniques such as phacoemulsification, hydrodissection, CCC, and various types of small incision surgery have led to significant modifications in IOL design. The change in 1-piece, biconvex, PMMA IOLs to a downsized diameter of 12.0 to 12.5 mm and optic size of 5.5 mm, along with a reduction in haptic angulation in the anterior-posterior plane to near planar, has resulted in a new generation of lenses designed specifically for inthe-bag implantation after CCC. Apple, 12 who termed this IOL design capsular, documented and summarized the advantages of capsular IOLs, basing his observations on clinicopathological and experimental studies. The small capsular IOL design is a reasonable choice for surgeons who desire to continue using an open-loop PMMA IOL, want an IOL that is relatively easy to insert, and are not ready to make the transition to a foldable IOL. Our study suggests that cataract surgery using phacoemulsification with CCC and a small capsular design, biconvex, PMMA IOL has no significant effect on the subsequent need for Nd:YAG laser capsulotomy when compared with a biconvex PMMA IOL with a larger diameter and optic size and increased haptic angulation to 10 degrees. Given our data power calculations, an observable difference of more than 11% in the 3 year Nd:YAG rate between the 2 IOL groups would have been detected by our study. Studies 1·4·5•7•8 have shown a reduction in the epithelial pearl form of PCO in IOLs that enhance contact between the posterior surface of the IOL optic and the anterior surface of the posterior capsule. This contact
creates a mechanical barrier effect that inhibits migration of lens epithelial cells onto the posterior capsule. Laboratory studies suggest that optic and overall lens diameters have a limited effect on the amount of contact between the IOL and posterior capsule. 4·13 Our clinical study found no difference in the Nd:YAG laser capsulotomy rate between the small capsular IOL and the larger IOL, corroborating this observation. In contrast, 1 recent clinical study9 suggests that smaller IOLs lead to a lower incidence of PC0. 9 Small capsular IOLs also have reduced haptic angulation, which facilitates insertion of the IOL through a tunnel incision into the capsular bag. In contrast, highly angulated IOLs can be more difficult to insert through a tunnel incision into the capsular bag. Conceptually, reducing the haptic angulation would reduce the posterior positioning of the optic, decreasing the contact with the posterior capsule and thus possibly increasing the incidence of the epithelial form of PC0. 4·7•13 Clinically, we did not detect a difference between the 2 groups with respect to the degree of contact between the posterior capsule and the posterior surface of the optic. Our study did show, however, that reducing haptic angulation from 10 to 2 degrees had no significant effect on the subsequent Nd:YAG laser capsulotomy rate. Our study did not distinguish between the epithelial pearl form of PCO and the fibrosis form. The fibrosis form may be more difficult to prevent, and the advantage of the IOrs barrier effect in preventing this type of PCO is less clear. A recent study of PMMA IOLs comparing a biconvex with a convex-plano design suggests that increased contact between the optic and posterior capsule may increase the incidence of PCO after phacoemulsification and CCC. 14 A multifactorial pathogenesis of PCO is suggested by the marked variation in the incidence of this problem among surgeons, whose individual technique is idiosyncratic and whose IOL selection is personalized. Resolution of PCO might be limited by current technologies and may require the impetus of improved surgical technique and further refinements in IOL design.
References 1. Sterling S, Wood TO. Effect of intraocular lens convexity on posterior capsule opacification. J Cataract Refract Surg 1986; 12:655-657
J CATARACf REFRACf SURG-VOL 24, SEPTEMBER 1998
1241
EFFECT OF IOL DESIGN ON ND:YAG RATES
2. Lindstrom RL, Harris WS. Management of the posterior capsule following posterior chamber lens implantation. Am Intra-Ocular Implant Soc J 1980; 6:255-258 3. Percival SPB, Setty SS. Analysis of the need for secondary capsulotomy during a five-year follow-up. J Cataract Refract Surg 1988; 14:379-382 4. Apple DJ, Solomon KD, Tetz MR, et al. Posterior capsule opacification. Surv Ophthalmol 1992; 37:73116 5. Born CP, Ryan DK. Effect of intraocular lens optic design on posterior capsular opacification. J Cataract Refract Surg 1990; 16:188-192 6. Frezwtti R, Caporossi A. Pathogenesis of posterior capsular opacification. Part I: epidemiological and clinicostatistical data. J Cataract Refract Surg 1990; 16:347352 7. Downing JE. Long-term discission rate after placing posterior chamber lenses with the convex surface posterior. J Cataract Refract Surg 1986; 12:651-654 8. Martin RG, Sanders DR, Souchek J, et al. Effect of posterior chamber intraocular lens design and surgical placement on postoperative outcome. J Cataract Refract Surg 1992; 18:333-341 9. Mamalis N, Crandall AS, Linebarger E, et al. Effect of intraocular lens size on posterior capsule opacification
1242
10.
11.
12. 13.
14.
after phacoemulsification. J Cataract Refract Surg 1995; 21:99-102 Jamal SA, Solomon LD. Risk factors for posterior capsular pearling after uncomplicated extracapsular cataract extraction and plano-convex posterior chamber lens implantation. J Cataract Refract Surg 1993; 19:333338 Mantel N. Synthetic retrospective studies and related topics. Biometrics 1973; 29:479-486 Apple DJ. Intraocular lens biocompatibility (guest editorial). J Cataract Refract Surg 1992; 18:217-218 Wesendahl TA, Hunold W, Auffarth GU, Apple DJ. Kontacktbereich von Kundinse und Hinterkapsel; Systematische untersuchung unterschiedlicher Haptikparameter. Ophthalmologe 1994; 91:680-684 Yamada K, Nagamoto T, Yozawa H, et al. Effect of intraocular design on posterior capsule opacification after continuous curvilinear capsulorhexis. J Cataract Refract Surg 1995; 21:697-700
Supported in part by an unrestricted grant from Research to Prevent Blindness, Inc., New York, New York, and Mayo Foundation, Rochester, Minnesota, USA. None of the authors has a commercial or proprietary interest in any product or instrument mentioned.
J CATARACT REFRACT SURG-VOL 24, SEPTEMBER 1998
ABSTRACT Purpose: To compare the effect of 2 poly(methyl methacrylate) (PMMA), 1-piece, biconvex intraocular lens (IOL) designs on the cumulative frequency of neodymium:YAG (Nd :YAG) laser posterior capsulotomy. Setting: Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota, USA. Methods: This retrospective study evaluated 369 eyes that had phacoemulsification with continuous curvilinear capsulorhexis (CCC) and IOL implantation in the capsular bag . Patients were placed in 1 of 2 groups based on the 1-piece, biconvex PMMA IOL design: large IOL, with a lens diameter of 13.50 to 13.75 mm, optic size of 6.5 mm, and 10 degree haptic angulation; small capsular IOL, with a lens diameter of 12.0 to 12.5 mm, optic size of 5.5 mm, and 2 degree haptic angulation. Results: Using Kaplan-Meier analysis, the frequency of Nd:YAG laser posterior capsulotomy 1, 2, and 3 years after cataract surgery was 1.6, 12.3, and 26.5%, respectively, in the large IOL group and 3.4, 9.5, and 23.5% , respectively, in the small capsular IOL group. The cumulative frequency of Nd:YAG laser capsulotomy was not statistically different between the 2 groups. Conclusion: After phacoemulsification and CCC, there was no significant difference in the Nd:YAG laser capsulotomy rate in eyes with a small , capsular design, 1-piece, biconvex PMMA IOL and those with a larger, angulated , 1-piece, biconvex PMMA IOL. J Cataract Refract Surg 1998; 24:1239-1242
P
osterior capsule opacification (PCO) is a common complication of cataract extraction with intraocular lens (IOL) implantation, approaching 50% in early investigations of poly(methyl methacrylate) (PMMA) 10Ls. 1-4 Studies have shown that the amount of PCO can vary considerably with the design and configura-
From the Department of Ophthalmology (Erie, Hardwig) and Section ofBiostatistics (Hodge), Mayo Clinic and Mayo Foundation, Rochester, Minnesota, USA. Reprint requests to jay C. Erie, MD, Mayo Clinic, Department of Ophthalmology, 200 First Street SW, Rochester, Minnesota 55905, USA.
tion of the PMMA IOL.4-7 Since these studies, significant modifications in PMMA IOL design have occurred as a result of new technology and the introduction of surgical techniques such as phacoemulsification and continuous curvilinear capsulorhexis (CCC). These modifications in PMMA IOL design include a change to a 1-piece, biconvex, PMMA IOL, a trend toward downsizing the total diameter to 12.0 to 12.5 mm and the optic size to 5.5 mm, and a reduction in haptic angulation to near planar. It is thought that this new generation of PMMA IOLs, designed for in-the-bag implantation after CCC, provides a better physiologic match between anatomy and IOL. Information on the possible impact of this IOL design change on the
J CATARACT REFRACT SURG-VOL 24, SEPTEMBER 1998
1239
EFFECT OF IOL DESIGN ON ND:YAG RATES
neodymium:YAG (Nd:YAG) laser posterior capsulotomy rate is limited. 8·9 We studied the effect of 2 posterior chamber PMMA IOL designs on the frequency ofNd:YAG laser capsulotomy for PCO after phacoemulsification and CCC.
Patients and Methods This retrospective study comprised 369 patients who had cataract extraction by phacoemulsification with CCC and IOL implantation in the capsular bag. The surgeries were performed by 1 of 2 surgeons (J.C.E., P.WH.) from January 1, 1990, through December 31, 1993, using a similar technique and modified retrobulbar anesthesia. After a scleral groove and shelving of the wound, a viscoelastic material was inserted into the anterior chamber and a CCC performed with a forceps. The nucleus was hydrodissected and removed by phacoemulsification and the divide and conquer technique. The remaining cortex was removed with an automated irrigation/aspiration handpiece. Mter viscoelastic material was injected into the capsular bag, the posterior chamber IOL was placed directly in the bag. The viscoelastic material was removed and the wound dosed with a running or interrupted 10-0 nylon suture. All patients received a subconjunctival injection of dexamethasone phosphate 0.1 o/o (Decadron®). Patients were excluded from the study if they had cataract extraction by means other than CCC with phacoemulsification, had an incomplete CCC with tear(s) of the anterior capsule, had additional procedures at the time of the cataract surgery, did not have the IOL placed within the capsular bag, had complications with posterior capsule rupture or vitreous loss, or received a foldable IOL. The decision to perform an Nd:YAG laser capsulotomy was based on subjective patient complaints of visual loss coupled with objective findings of significant PCO caused by posterior capsule fibrosis, Elschnig pearls, or both as seen on dilated biomicroscopy. Patients were divided into 2 groups according to the type of IOL implanted: a large IOL group with a 10 degree angulated, 6.5 mm optic, 13.50 to 13.75 mm diameter, 1-piece biconvex PMMA IOL (Storz 650 CUV or Pharmacia 720); a small capsular IOL group with a 1240
2 degree angulated, 5.5 mm optic, 12.0 to 12.5 mm diameter, 1-piece biconvex PMMA IOL (Storz 359 or Pharmacia 815). The 2 IOL types within each group were of the same design except for a small difference in lens diameter (0.25 to 0.50 mm). Both groups were age matched as it has been reported that PCO increases in younger patients. 10 The cumulative frequency ofNd:YAG laser capsulotomy was calculated using Kaplan-Meier survival analysis to eliminate the influence of different lengths of follow-up. The difference in the Nd:YAG posterior capsulotomy rate between the 2 groups was calculated using the log-rank test. Differences between the large and small capsular IOL groups with respect to sex were evaluated using the chi-square test for independence. 11
Results Table 1 shows the IOL characteristics of patients in each group. The percentage of Nd:YAG laser posterior capsulotomy using the Kaplan-Meier method 1, 2, and 3 years after cataract surgery was 1.6, 12.3, and 26.5%, respectively, in the large IOL group and 3.4, 9.5, and 23.5%, respectively, in the small capsular IOL group (Figure 1). The cumulative frequency ofNd:YAG laser capsulotomy was not statistically different between the 2 groups. Data power calculations predicted an 80% power to detect an 11 o/o difference in the 3 year Nd:YAG rate between the 2 groups. There was no significant difference between sexes.
Table 1. Patient characteristics. Group Large IOL
SmaiiiOL
198
171
80
77
118
94
Mean
66 :±: 15
67 :±: 13
Range
17-93
16-93
Mean
41
31
Range
6-77
6-64
Characteristic Number of patients Sex Male Female Age (years)
Follow-up (months)
J CATARACT REFRACT SURG--VOL 24, SEPTEMBER 1998
EFFECT OF IOL DESIGN ON ND:YAG RATES 100
~ ~
---- Small "capsular" IOL -
80
LargeiOL
c:
CD :I
C"
g CD
> ~ :; E :I
(.')
60 40 20
0
2
0
3
Years Figure 1. (Erie) Cumulative frequency of Nd:YAG laser capsulotomy after cataract surgery.
Discussion Advances in cataract surgery techniques such as phacoemulsification, hydrodissection, CCC, and various types of small incision surgery have led to significant modifications in IOL design. The change in 1-piece, biconvex, PMMA IOLs to a downsized diameter of 12.0 to 12.5 mm and optic size of 5.5 mm, along with a reduction in haptic angulation in the anterior-posterior plane to near planar, has resulted in a new generation of lenses designed specifically for inthe-bag implantation after CCC. Apple, 12 who termed this IOL design capsular, documented and summarized the advantages of capsular IOLs, basing his observations on clinicopathological and experimental studies. The small capsular IOL design is a reasonable choice for surgeons who desire to continue using an open-loop PMMA IOL, want an IOL that is relatively easy to insert, and are not ready to make the transition to a foldable IOL. Our study suggests that cataract surgery using phacoemulsification with CCC and a small capsular design, biconvex, PMMA IOL has no significant effect on the subsequent need for Nd:YAG laser capsulotomy when compared with a biconvex PMMA IOL with a larger diameter and optic size and increased haptic angulation to 10 degrees. Given our data power calculations, an observable difference of more than 11% in the 3 year Nd:YAG rate between the 2 IOL groups would have been detected by our study. Studies 1·4·5•7•8 have shown a reduction in the epithelial pearl form of PCO in IOLs that enhance contact between the posterior surface of the IOL optic and the anterior surface of the posterior capsule. This contact
creates a mechanical barrier effect that inhibits migration of lens epithelial cells onto the posterior capsule. Laboratory studies suggest that optic and overall lens diameters have a limited effect on the amount of contact between the IOL and posterior capsule. 4·13 Our clinical study found no difference in the Nd:YAG laser capsulotomy rate between the small capsular IOL and the larger IOL, corroborating this observation. In contrast, 1 recent clinical study9 suggests that smaller IOLs lead to a lower incidence of PC0. 9 Small capsular IOLs also have reduced haptic angulation, which facilitates insertion of the IOL through a tunnel incision into the capsular bag. In contrast, highly angulated IOLs can be more difficult to insert through a tunnel incision into the capsular bag. Conceptually, reducing the haptic angulation would reduce the posterior positioning of the optic, decreasing the contact with the posterior capsule and thus possibly increasing the incidence of the epithelial form of PC0. 4·7•13 Clinically, we did not detect a difference between the 2 groups with respect to the degree of contact between the posterior capsule and the posterior surface of the optic. Our study did show, however, that reducing haptic angulation from 10 to 2 degrees had no significant effect on the subsequent Nd:YAG laser capsulotomy rate. Our study did not distinguish between the epithelial pearl form of PCO and the fibrosis form. The fibrosis form may be more difficult to prevent, and the advantage of the IOrs barrier effect in preventing this type of PCO is less clear. A recent study of PMMA IOLs comparing a biconvex with a convex-plano design suggests that increased contact between the optic and posterior capsule may increase the incidence of PCO after phacoemulsification and CCC. 14 A multifactorial pathogenesis of PCO is suggested by the marked variation in the incidence of this problem among surgeons, whose individual technique is idiosyncratic and whose IOL selection is personalized. Resolution of PCO might be limited by current technologies and may require the impetus of improved surgical technique and further refinements in IOL design.
References 1. Sterling S, Wood TO. Effect of intraocular lens convexity on posterior capsule opacification. J Cataract Refract Surg 1986; 12:655-657
J CATARACf REFRACf SURG-VOL 24, SEPTEMBER 1998
1241
EFFECT OF IOL DESIGN ON ND:YAG RATES
2. Lindstrom RL, Harris WS. Management of the posterior capsule following posterior chamber lens implantation. Am Intra-Ocular Implant Soc J 1980; 6:255-258 3. Percival SPB, Setty SS. Analysis of the need for secondary capsulotomy during a five-year follow-up. J Cataract Refract Surg 1988; 14:379-382 4. Apple DJ, Solomon KD, Tetz MR, et al. Posterior capsule opacification. Surv Ophthalmol 1992; 37:73116 5. Born CP, Ryan DK. Effect of intraocular lens optic design on posterior capsular opacification. J Cataract Refract Surg 1990; 16:188-192 6. Frezwtti R, Caporossi A. Pathogenesis of posterior capsular opacification. Part I: epidemiological and clinicostatistical data. J Cataract Refract Surg 1990; 16:347352 7. Downing JE. Long-term discission rate after placing posterior chamber lenses with the convex surface posterior. J Cataract Refract Surg 1986; 12:651-654 8. Martin RG, Sanders DR, Souchek J, et al. Effect of posterior chamber intraocular lens design and surgical placement on postoperative outcome. J Cataract Refract Surg 1992; 18:333-341 9. Mamalis N, Crandall AS, Linebarger E, et al. Effect of intraocular lens size on posterior capsule opacification
1242
10.
11.
12. 13.
14.
after phacoemulsification. J Cataract Refract Surg 1995; 21:99-102 Jamal SA, Solomon LD. Risk factors for posterior capsular pearling after uncomplicated extracapsular cataract extraction and plano-convex posterior chamber lens implantation. J Cataract Refract Surg 1993; 19:333338 Mantel N. Synthetic retrospective studies and related topics. Biometrics 1973; 29:479-486 Apple DJ. Intraocular lens biocompatibility (guest editorial). J Cataract Refract Surg 1992; 18:217-218 Wesendahl TA, Hunold W, Auffarth GU, Apple DJ. Kontacktbereich von Kundinse und Hinterkapsel; Systematische untersuchung unterschiedlicher Haptikparameter. Ophthalmologe 1994; 91:680-684 Yamada K, Nagamoto T, Yozawa H, et al. Effect of intraocular design on posterior capsule opacification after continuous curvilinear capsulorhexis. J Cataract Refract Surg 1995; 21:697-700
Supported in part by an unrestricted grant from Research to Prevent Blindness, Inc., New York, New York, and Mayo Foundation, Rochester, Minnesota, USA. None of the authors has a commercial or proprietary interest in any product or instrument mentioned.
J CATARACT REFRACT SURG-VOL 24, SEPTEMBER 1998