Evaluating and defining the sharpnessof intraocular lenses: Microedge structureof commercially available square-edged

hydrophilic intraocular lensesLiliana Werner, MD, PhD, Manfred Tetz, MD, Ines Feldmann, Dip Ing (FH), Michael Bucker, Dr Ing

PURPOSE: To evaluate the microstructure of the edges of currently available hydrophilic acrylicintraocular lenses (IOLs) in terms of their deviation from an ‘‘ideal’’ square as a follow-up of pre-liminary in vitro studies of experimental poly(methyl methacrylate) IOLs and commercially availablefoldable hydrophobic IOLs.

SETTING: Berlin Eye Research Institute, Berlin, Germany.

METHODS: Twenty-four designs of hydrophilic acrylic IOLs were used in this study. For eachdesign, a C20.0 diopter (D) IOL and a C0.0 D IOL (or the lowest available plus dioptric power)were evaluated. The IOL edge was imaged under low-vacuum (0.7 torr), high-magnification scan-ning electron microscopy (SEM) using an environmental microscope and standardized technique.The photographs were imported to a digital computer program, and the area above the posterior–lateral edge, representing the deviation from a perfect square, was measured in square microns.

RESULTS: Currently available hydrophilic acrylic IOLs labeled as square edged had an area ofdeviation from a perfect square ranging from 60.84 to 871.51 mm2 for the C20.0 D IOLs andfrom 35.52 to 826.55 mm2 for the low-diopter IOLs. Although some differences in edge finishingbetween the IOLs analyzed were observed, edge surfaces of hydrophilic acrylic IOLs appeared over-all smooth under environmental SEM.

CONCLUSIONS: Analysis of the microstructure of the optic edge of currently available square-edgedhydrophilic acrylic IOLs showed a large variation of the deviation area from a perfect square.

J Cataract Refract Surg 2009; 35:556–566 Q 2009 ASCRS and ESCRS

LABORATORY SCIENCE

Posterior chamber intraocular lenses (IOLs) witha square posterior optic edge have been associatedwith better posterior capsule opacification (PCO)prevention than round-edged IOLs, regardless of thematerial used in their manufacture.1–5

Tetz andWildeck6made the first attempt to evaluateand quantify the edge structure of IOLs at the micro-scopic level. They experimentally evaluated the opti-mum microedge profile of an IOL to prevent lensepithelial cell (LEC)migration in culture. Experimentalpoly(methyl methacrylate) (PMMA) IOLs with differ-ent edge profiles were imaged under scanning electronmicroscopy (SEM), and the area above the edge, repre-senting the deviation from an ideal square, was calcu-lated with a digital system (Evaluation of PosteriorCapsule Opacification systemdEPCO 2000 program.Available at: http://www.epco2000.de. AccessedDecember 9, 2008).7 In the second part of that study,8

Q 2009 ASCRS and ESCRS

Published by Elsevier Inc.

556

we used an improvedmethodology to evaluate the op-tic microedge structure of currently available hydro-phobic IOLs marketed as square-edged IOLs. In thecurrent study, we used the same methodology to eval-uate the microedge structure of currently availablesquare-edged hydrophilic acrylic IOLs. EnvironmentalSEM (ESEM) was used because most hydrophilicacrylic IOLs have a water content in the vicinity of26% and their edges may therefore be significantlymodified during the vacuum required in standardSEM procedures.

MATERIALS AND METHODS

Commercially available hydrophilic acrylic IOLs were ob-tained for use in this study through letters sent to majorIOLmanufacturers. All IOLs aremarketed as having a squareoptic edge for PCO prevention. Two IOLs of each designwere evaluated: a C20.0 diopter (D) and a C0.0 D (when

0886-3350/09/$dsee front matter

doi:10.1016/j.jcrs.2008.11.042

557LABORATORY SCIENCE: MICROEDGE STRUCTURE OF SQUARE-EDGED HYDROPHILIC IOLs

available) model of a particular design. If a C0.0 D modelwas not available, the lowest dioptric power for that partic-ular design was used.

Environmental SEM analyses were performed by an expe-rienced technician (I.F.) at the Federal Institute for MaterialsResearch and Testing, Berlin, Germany. Each IOL was care-fully removed from its original fluid-containing packagingwith a toothless forceps and rinsed with distilled water.This was done by grasping the IOL by the haptics to avoidalterations to the optic component. Care was taken to iden-tify the anterior and posterior surfaces of the IOL, which inmany instances, especially for the 1-piece designs, requiredthe help of the corresponding manufacturers. The IOLswere carefully mounted on an ESEM support containinga central groove; the manipulations were done under a grossmicroscope. A small portion of the optic component was fitto the groove, and the IOL was fixated to the support verti-cally with a piece of black adhesive tape. For some IOLs, 1of the haptics had to be cut for stable mounting to obtainhigh-quality perpendicular scans of the IOL optic edge(Figure 1). The support containing the IOL was then fit toan ESEM (XL 30 ESEM, FEI Co.). During the ESEM examina-tion, the analysis of each optic edge was done from a perpen-dicular view under a pressure of 0.7 torr, a temperature of20�C, and an accelerating voltage of 15.0 kV. This ESEM tech-nique does not require previous coating of the IOLs. The per-pendicularity of the specimenwas adjusted with a geometricscale on the computer monitor screen of the ESEM. Photo-graphs of the optic edge of each IOL from a perpendicularview were obtained at 3 magnifications: �100, �250, and�1000. The first 2 magnifications were used to documentthe overall orientation of the specimen, and the �1000 mag-nification photographs were used for the microedge analysis(Figure 2). The mean time between opening of the IOL pack-age and complete ESEM photography was 20 minutes.

All of the following procedures were then performed bythe same observer (L.W.) following a protocol established

Submitted: September 2, 2008.Final revision submitted: November 14, 2008.Accepted: November 24, 2008.

From the Berlin Eye Research Institute (Werner, Tetz) and theFederal Institute for Materials Research and Testing (Feldmann,Bucker), Berlin, Germany; John A. Moran Eye Center (Werner),University of Utah, Salt Lake City, Utah, USA.

No author has a financial or proprietary interest in any material ormethod mentioned.

Supported by a 2007 Research Grant from the European Society ofCataract & Refractive Surgeons.

Presented in part at the XXVI Congress of the European Society ofCataract & Refractive Surgeons, Berlin, Germany, September 2008.

Matthias Muller, PhD, and Stephanie Kronenberg, MS, Berlin EyeResearch Institute, assisted with the overall organization of thestudy.

Corresponding author: Liliana Werner, MD, PhD, Berlin EyeResearch Institute, Alt-Moabit 98/99, D-10559, Berlin, Germany.E-mail: werner.liliana@gmail.com.

J CATARACT REFRACT SURG

in a previous study.8 Basically, the ESEM photographs ob-tained from each IOL were saved as electronic high-resolu-tion JPEG files. They were then imported into theAutoCAD LT 2000 system (Autodesk), a software programcommonly used in engineering and architecture for area cal-culations. The first step was to adjust the scale of the photo-graph into the program by using the reference barincorporated in each ESEM photograph on the bottom. Afterthe scale on each photograph was confirmed by measuringthe reference bar and the corresponding value was obtained,a reference circle of known radius divided in 4 quadrantsby 2 perpendicular lines passing through its center wasprojected onto the photograph. The position of the circlewas adjusted so that the end of both perpendicular lineswould touch the lateral and posterior IOL optic edges. Thecomputer mouse was used to delineate the area of the lat-eral–posterior IOL edge deviating from a perfect square, de-fined by the 2 perpendicular lines inside the reference circle.The measurement of the area was then calculated by the pro-gram and provided in square microns. This was done usingreference circles with 2 radii: 40.0 mm and 60.0 mm (Figure 2,C andD). Theminimum radius size of 40.0 mmwas chosen asa function of the size of the human LEC, which in vivo wasshown to have a size range of 8.0 to 21.0 mm in diameter,but with larger lengths.9

Data were entered into Excel worksheets, and statisticalanalyses were performed using the data-analysis tools incor-porated into the Excel program (Microsoft Office 2003, Mi-crosoft Corp.) by using the F-test for variances, 2-sample ttest, analysis of variance (ANOVA), and Kruskal-Wallistest. A P value less than 0.05 was considered statisticallysignificant.

RESULTS

Table 1 shows characteristics of the IOLs used in thisstudy, including the values of the area representingthe deviation from an ideal square measured in eachIOL with the AutoCAD system. Figures 3 to 7 showSEM photographs of the lateral–posterior edge of theIOLs used in this study, incorporated into the

Figure 1. Mounting of the IOLs before ESEM examination. The ar-row indicates the viewing direction in the ESEM (Acri.Tec Acri.Lyc523D, C0 D, SN 10955H5404004).

- VOL 35, MARCH 2009

558 LABORATORY SCIENCE: MICROEDGE STRUCTURE OF SQUARE-EDGED HYDROPHILIC IOLs

Figure 2. Environmental SEM andAutoCAD analyses of 1 IOL usedin this study (Oculentis L-302-1,C0.0 D, SN 20000135034). A: Per-pendicular view of the optic edgeobtained with a magnification of�100. All IOLs in this study wereoriented with the lateral edge up,and the anterior and posterior sur-faces on the right side and leftside, respectively. The ESEMphotos of �100 and �250 helpedcontrol the orientation of the speci-mens. B: Perpendicular view of theoptic lateral–posterior edge ob-tained with a magnification of�1000. The 20.0 mm bar was usedto adjust the scale of the photo-graph into the AutoCAD program.C and D: AutoCAD screens of theanalyses of the photograph in B us-ing 40.0 mm radius and 60.0 mm ra-dius circles, respectively. Note thatthe magnification of the photo-graphs on the screens was adjustedto incorporate the entire bottomright quadrant of each circle. Thearea in red corresponds to the devi-ation from the ideal square, and itwas measured as 99.44 mm2 and201.50 mm2, respectively.

AutoCAD analysis screen. Some of the IOLs showededges with particular characteristics (eg, sloped lat-eral–posterior edge, aspect with a ‘‘double’’ edge or‘‘enhanced’’ square edge). The arrows in Figure 8show the sites for the area measurement in the �1000magnification photographs of the IOLs with edges ex-hibiting particular characteristics. These were the siteswhere the position of the circles could be adjusted sothat the end of both perpendicular lines would touchthe lateral andposterior IOLoptic edges simultaneously.

With the exception of the Tekia Tek-LensII IOLs, allIOLs usedwere provided inside their original commer-cial packages. Two dioptric powers were analyzed foreach IOL design, with the exception of the Rayner MFLEX630F IOL, forwhichonlyaC19.5Dwasanalyzed.A C15.0 Dmodel and a C25.5 Dmodel were analyzedfor the Tekia Tek-LensII Model 611. A C0.0 D IOL wasnot available for the followingdesigns:Xcelens Idea; Te-kia Tek-LensII model 616; Acri.Tecmodels 47LC, 366D,and37A;Bausch&LombMI60; StaarCQ2015; andRay-ner Superflex 620H. Therefore, in these cases, alterna-tive low-diopter powers were analyzed (Table 1).

The mean area of deviation from a perfect square,measured with the 40.0 mm circle, was 379.01 mm2 G188.26 (SD) (range 60.84 to 871.51 mm2) for the C20.0 DIOLs (n Z 24) and 281.71 G 241 mm2 (range 35.52 to826.55 mm2) for the low-diopter IOLs (n Z 23); the dif-ference was not statistically significant (P Z .12). The

J CATARACT REFRACT SUR

mean area of deviation fromaperfect square,measuredwith the 40.0 mmcircle,was 280.44G 189.85mm2 (range35.52 to 826.55 mm2) for the 1-piece IOLs (n Z 33) and451.51 G 242.29 mm2 (range 130.2 to 871.51 mm2) forthe 3-piece IOLs (nZ 14); thedifferencewas statisticallysignificant (P Z .01). The mean area of deviation froma perfect square for all IOLs in the study (n Z 47) was331.39 G 218.90 mm2 (range 35.52 to 871.51 mm2).

The value measured with the 60.0 mm radius circlewas similar (1.05 times larger or smaller) to the valuemeasured with the 40.0 mm radius circle for IOLs 15and 26. The other IOLs had area values measuredwith the 60.0 mm radius circle that were generally atleast 1.5 times larger than the values measured withthe 40.0 mm radius circle, and this was mostly a func-tion of the convexity of their posterior optic surface.

The ESEM evaluation also allowed for assessment ofthe surface characteristics of the optic edge of the IOLs.Although some differences in edge finishing betweenthe IOLs analyzed were seen, edge surfaces of hydro-philic acrylic IOLs appeared overall smooth underESEM. Mild irregularities were observed on the sur-face of IOLs 1, 15, 25, and 43.

DISCUSSION

According to experimental studies, the preventativePCO effect associated with the square edge may be

G - VOL 35, MARCH 2009

559LABORATORY SCIENCE: MICROEDGE STRUCTURE OF SQUARE-EDGED HYDROPHILIC IOLs

Table 1. Characteristics of IOLs used in this study.

IOL* Manufacturer ModelDioptricPower

IDNumber Design Optic Type Area 40 Area 60

1 Oculentis L-301-1 C0.0 SN 20000077779 1 piece withclosed loops

Monofocal 121.96 197.00

2 Oculentis L-301-1 C20.0 SN 20000128526 1 piece withclosed loops

Monofocal 261.50 635.71

3 Oculentis L-302-1 C0.0 SN 20000135034 1 piecewith loops

Monofocal 99.44 201.50

4 Oculentis L-302-1 C20.0 SN 20000135096 1 piecewith loops

Monofocal 224.54 556.30

5 Oculentis L-303 C0.0 SN 20000072587 1 piece,plate type

Monofocal 112.91 305.60

6 Oculentis L-303 C20.0 SN 20000134169 1 piece,plate type

Monofocal 183.25 373.90

7 Oculentis L-402 C0.0 SN 20000094130 3 piece Monofocal 130.20 259.168 Oculentis L-402 C20.0 SN 20000134754 3 piece Monofocal 363.13 799.899 Oculentis LS-502-1 C0.0 SN 20000102168 1 piece

with loopsMonofocal

(blue-light filter)95.39 228.26

10 Oculentis LS-502-1 C20.0 SN 20000121888 1 piecewith loops

Monofocal(blue-light filter)

300.58 657.60

11 Xcelens Idea C5.0 SN 609261181547012 1 piecewith loops

Monofocal 408.02 890.41

12 Xcelens Idea C20.0 SN 605231177555016 1 piecewith loops

Monofocal 753.78 1653.22

13 Morcher 92S C0.0 SN 1293098 1 piecewith loops

Monofocal 826.55 1579.81

14 Morcher 92S C20.0 SN 1338748 1 piecewith loops

Monofocal 317.99 374.74

15 Dr. Schmidt (MicroCryl)MC X11 ASP

C0.0 Lot 563225-096 1 piece,plate type

Monofocal,aspheric

35.52 33.89

16 Dr. Schmidt (MicroCryl)MC X11 ASP

C20.0 Lot 022287-875 1 piece,plate type

Monofocal,aspheric

60.84 259.43

17 Tekia Tek-LensII 616 C6.0 SN G12210905 3 piece Monofocal 316.64 673.6318 Tekia Tek-LensII 611 C15.0 SN F11230078 3 piece Monofocal 188.85 429.2519 Tekia Tek-LensII 611 C25.5 SN F11230118 3 piece Monofocal 372.86 841.2820 Acri.Tec Acri.Lyc 44S C0.0 SN 23377H5710601 1 piece,

plate typeMonofocal 122.32 343.51

21 Acri.Tec Acri.Lyc 44S C20.0 SN 20787H8077404 1 piece,plate type

Monofocal 221.49 569.16

22 Acri.Tec Acri.Lyc 47S C0.0 SN 14457H5306905 1 piecewith loops

Monofocal 108.29 221.28

23 Acri.Tec Acri.Lyc 47S C20.0 SN 15477H5302113 1 piecewith loops

Monofocal 382.26 838.30

24 Acri.Tec Acri.Lyc 47LC C1.0 SN 23587H5753201 1 piecewith loops

Monofocal,aspheric

90.61 173.87

25 Acri.Tec Acri.Lyc 47LC C20.0 SN 19167H5635214 1 piecewith loops

Monofocal,aspheric

255.22 490.73

26 Acri.Tec Acri.LISA 366D C1.0 SN 23087H5766302 1 piece,plate type

Bifocal,aspheric

65.06 68.89

27 Acri.Tec Acri.LISA 366D C20.0 SN 17127H5450812 1 piece,plate type

Bifocal,aspheric

329.79 716.74

28 Acri.Tec Acri.Lyc 523D C0.0 SN 10955H5404004 3 piece Bifocal, aspheric 794.60 1782.3329 Acri.Tec Acri.Lyc 523D C20.0 SN 09306H8101504 3 piece Bifocal, aspheric 871.51 1796.7030 Acri.Tec Acri.Lyc 527D C0.0 SN 10955H5403905 3 piece Bifocal, aspheric 805.26 1798.0931 Acri.Tec Acri.Lyc 527D C20.0 SN 13026H5413905 3 piece Bifocal, aspheric 687.32 1509.70

J CATARACT REFRACT SURG - VOL 35, MARCH 2009

560 LABORATORY SCIENCE: MICROEDGE STRUCTURE OF SQUARE-EDGED HYDROPHILIC IOLs

Table 1 (Cont. )

IOL* Manufacturer ModelDioptricPower

IDNumber Design Optic Type Area 40 Area 60

32 Acri.Tec Acri.Lyc 37A C10.0 SN 15547H5553003 1 piecewith loops

Monofocal,aspheric

246.96 468.65

33 Acri.Tec Acri.Lyc 37A C20.0 SN 01737H9058813 1 piecewith loops

Monofocal,aspheric

288.73 679.58

34 Bausch & Lomb Akreos Adapt C0.0 SN 5719701019 1 piece, plate typewith 4 loops

Monofocal 275.80 468.41

35 Bausch & Lomb Akreos Adapt C20.0 SN 5716686029 1 piece, plate typewith 4 loops

Monofocal 263.33 463.01

36 Bausch & Lomb MI60 C20.0 SN 1726014038 1 piece, plate typewith 4 loops

Monofocal,aspheric

474.32 561.89

37 Bausch & Lomb MI60 C10.0 SN 1620514001 1 piece, plate typewith 4 loops

Monofocal,aspheric

311.04 425.14

38 Staar CQ2015 (Collamer) C10.5 SN B183414 3 piece Monofocal 331.66 488.8039 Staar CQ2015 (Collamer) C20.0 SN B192129 3 piece Monofocal 398.28 725.4240 Rayner Superflex 620H C1.0 Lot 107E 75983 46 1 piece

with closed loopsMonofocal 266.95 538.63

41 Rayner Superflex 620H C20.0 Lot 107E 76002 58 1 piecewith closed loops

Monofocal 343.96 427.69

42 Rayner M FLEX 630F C19.5 Lot 107E 76564 02 1 piecewith closed loops

Multifocal 262.76 431.67

43 Technomed EasyCare 600 C0.0 SN F03100002 3 piece Monofocal 195.85 461.2344 Technomed EasyCare 600 C20.0 SN H09120005 3 piece Monofocal 414.82 842.3945 Technomed EasAcryl 100 Plus C0.0 SN 349061 1 piece

with loopsMonofocal 529.54 922.83

46 Technomed EasAcryl 100 Plus C20.0 SN 793781 1 piecewith loops

Monofocal 613.82 1211.69

47 Tekia Tek-LensII 616 C20.0 S/O F320818, SN 22 3 piece Monofocal 450.27 927.99

IOL Z intraocular lens*The IOLs were numbered according to the order they were received at the Berlin Eye Research Institute.

due to a mechanical barrier effect,10,11 the contact in-hibition of migrating LECs at the capsular bend cre-ated by the edge,12,13 the higher pressures exerted byIOLs with a square-edged optic profile on the poste-rior capsule,14,15 or different combinations of all3 factors.

In the first part of this study,6 the optimum micro-edge design feature of an IOL to prevent LEC migra-tion was evaluated in an in vitro setting. Plano C0.0D PMMA IOLs with 11 defined edge designs werespecially manufactured. To obtain different edge de-signs, the IOLs were removed from the tumble-polish-ing machine at different times. To evaluate the opticedges, standardized SEM pictures were taken from 1IOL in each groupwith an enlargement of�500. A dig-ital computer system (EPCO 2000 program)7 was usedto evaluate the area above the edges on the SEM pho-tographs. To achieve this, the area had to be defined asthe deviation from an ideal rectangular projection. Theedge’s ability to stop cell growth was observed byplacing each IOL into cell culture and observing bo-vine LEC growth over 18 days on average. Only 3

J CATARACT REFRACT SUR

groups of IOLs, those with the sharpest edge design,prevented the growth of LECs on the visual axis ofthe IOL.

In the second part of the study,8 we used the Auto-CAD program to calculate the area of deviation froman ideal square formed by the lateral–posterior edgesof currently available, square edge, hydrophobicIOLs. Measurement with this program was easy be-cause it allowed great flexibility in the adjustment ofthe measurement scale and also on the projection ofstructures of known dimensions onto the photo-graphs. Projection of the 2 circles of known radius,with 2 perpendicular lines crossing their centers,helped standardize the measurements. Indeed, oneach �1000 SEM photograph used, there was only 1site for each circle where the 2 lines touched the lateraland posterior edges of the IOL. Considering the mea-surements done with the 40.0 mm radius circle, themean values for hydrophobic acrylic IOLs (n Z 19)and silicone IOLs (n Z 11) were 183.38 G 82.18 mm2

and 74.39 G 88.54 mm2, respectively (all dioptricpowers evaluated included).

G - VOL 35, MARCH 2009

561LABORATORY SCIENCE: MICROEDGE STRUCTURE OF SQUARE-EDGED HYDROPHILIC IOLs

Figure 3. AutoCAD screens of theanalyses (40.0 mm radius circle) ofESEM photographs obtained fromthe Oculentis study IOLs (IOLnumbers correspond to those inTable 1).

In the current study, we used the same protocol as inthe second part to evaluate hydrophilic acrylic de-signs, with the only difference being that ESEM wasused to evaluate the IOLs under low vacuum condi-tions, preventing dehydration. We found that thearea measurement values of hydrophilic acrylicIOLs, as a group, were higher than the values reportedfor hydrophobic acrylic or silicone IOLs (mean 331.39G 218.90 mm2; n Z 47 IOLs). The area value of the ref-erence square-edged IOL used in the second part ofthis study was 34.0 mm2.8 Seven silicone IOLs hadarea values that were close to that of the referenceIOL, while this was observed with only 1 hydrophilicacrylic IOL in the current study. The ANOVA andKruskal-Wallis tests give a P value of less than 0.001to the comparison of the area values of the 19 hydro-phobic acrylic, 11 silicone, and 47 hydrophilic acrylicIOLs measured using the same standardized tech-nique in the second part and the current study. Theseconclusions may, however, be limited by the fact thatthe IOLs were analyzed in 2 different microscopic set-tings, the number of IOLs analyzed for each material

J CATARACT REFRACT S

was different, and there are other designs availableon the market that were not represented in this seriesof studies.

Nanavaty et al.16 also performed a study compar-ing the edge profile of commercially availablesquare-edged IOLs. Their study included 17 square-edged designs of C20.0 D, with 5 hydrophobicacrylic, 7 hydrophilic acrylic, and 5 silicone IOLs.The IOLs were evaluated under ESEM using thesame temperature and pressure conditions as in thecurrent study. Perpendicular images with amagnifica-tion of �500 were obtained and analyzed by usingpurpose-designed software to produce a line tracingof the edge profile of the IOLs. The sharpness of theedge profile was then quantified by measuring the lo-cal radius of curvature at the point on the posterioredge with the smallest radius. The mean radius ofcurvature in the hydrophobic acrylic, hydrophilicacrylic, and silicone IOL groups was 11.2 G 4.9 mm,16.0 G 3.4 mm, and 8.5 G 0.6 mm, respectively. Al-though these authors used a different quantificationtechnique, a smaller number of designs in each

URG - VOL 35, MARCH 2009

562 LABORATORY SCIENCE: MICROEDGE STRUCTURE OF SQUARE-EDGED HYDROPHILIC IOLs

Figure 4. AutoCAD screens of theanalyses (40.0 mm radius circle) ofESEM photographs obtained fromthe Xcelens (11 and 12), Morcher(13 and 14), and Dr. Schmidt (15and 16) study IOLs (IOL numberscorrespond to those in Table 1).

material group, and only C20.0 D IOLs, their conclu-sions are comparable to ours in that as a group, hy-drophilic acrylic IOLs appear to have relativelyrounder edges than hydrophobic acrylic IOLs and sil-icone IOLs. This is probably due to the manufacturingprocess of hydrophilic acrylic IOLs, which involveslathe cut from dehydrated blocks that are then rehy-drated. Water absorption by the IOL material mayrender the final aspect of the edge rounder as theIOL swells. However, considering the relatively lowerarea values measured for some IOLs in this study (eg,some of the Oculentis, Dr. Schmidt, and Acri.Tec de-signs; Table 1), one may conclude that it is possible tomanufacture hydrophilic acrylic IOLs with sharperedges.

Our results are interesting in the light of clinicalstudies comparing square-edged IOLs manufacturedfrom different materials that report higher rates of

J CATARACT REFRACT SUR

PCO with hydrophilic acrylic IOLs. Kugelberget al.17 evaluated 120 eyes of 120 patients who hadphacoemulsification and were prospectively random-ized to receive a square-edged hydrophobic acrylic(Alcon SA60AT) or a square-edged hydrophilic acrylicIOL (Bausch & Lomb BL27). Both IOLs are 1-piece de-signs with an optic diameter of 6.0 mm and no optic–haptic angulation. At the 1-year follow-up, there wasa statistically significant difference in PCO betweenthe 2 groups, with the hydrophilic acrylic group hav-ing a greater area and severity of PCO as analyzedwith POCOman software.18 At the 2-year follow-upof the same study, patients with the SA60AT hydro-phobic acrylic IOL still had less PCO as well as betterhigh- and low-contrast visual acuity than patients withthe BL27 hydrophilic acrylic IOL.19

Richter-Mueksch et al.20 evaluated the uveal andcapsular biocompatibility of 86 eyes of 78 patients

G - VOL 35, MARCH 2009

563LABORATORY SCIENCE: MICROEDGE STRUCTURE OF SQUARE-EDGED HYDROPHILIC IOLs

with pseudoexfoliation who had cataract surgery. Ina nonrandomized protocol, the eyes received 1 of thefollowing squared-edged IOLs: OphthalMed Injecta-cryl F3000 (hydrophilic acrylic), Alcon AcrySofMA60MB (hydrophobic acrylic), or Pharmacia CeeOn

911 (silicone). Posterior capsule opacification wasstatistically greater in the hydrophilic acrylic group,according to semiquantitative analyses.

In a metaanalysis including 23 prospective random-ized controlled clinical trials,21 the authors concluded

Figure 6. AutoCAD screens of theanalyses (40.0 mm radius circle) ofESEM photos obtained from the Te-kia (17 to 19, 47), and Bausch &Lomb (34 to 37) study IOLs (IOLnumbers correspond to those inTable 1).

Figure 5. AutoCAD screens of theanalyses (40.0 mm radius circle) ofESEM photos obtained from theAcri.Tec study IOLs (IOL numberscorrespond to those in Table 1).

J CATARACT REFRACT SURG - VOL 35, MARCH 2009

564 LABORATORY SCIENCE: MICROEDGE STRUCTURE OF SQUARE-EDGED HYDROPHILIC IOLs

Figure 7. AutoCAD screens of theanalyses (40 mm radius circle) ofESEM photographs obtained fromthe Staar (38 and 39), Rayner (40to 42), and Technomed (43 to 46)study IOLs (IOL numbers corre-spond to those in Table 1).

that hydrophilic acrylic IOLs were significantly associ-ated with higher rates of PCO and neodymium:YAGlaser posterior capsulotomies than IOLs of other mate-rials. However, the majority of the studies included inthe analysis involved hydrophilic acrylic IOLs notmarketed as square-edged IOLs.

Finally, in a prospective randomized study, Heatleyet al.22 evaluated 106 eyes of 53 patients with bilateralcataract. One eye was implanted with an SA60ATIOL and the other, with a Rayner Centerflex 570HIOL (1-piece design with square edges and no optic–haptic angulation). The percentage PCO area, mea-sured with the POCOman system, was higher in thehydrophilic IOL group than in the hydrophobic IOLgroup at 1 month (P!.05), 6 months (P!.001), and12months (P!.001). At 1 year, themedian PCOvalueswere 50.3% in the hydrophilic IOL group and 4.9%in the hydrophobic IOL group. Incorporation of an‘‘enhanced’’ square edge into this IOL design clearlyimproved PCO results, as shown in rabbit and clinicalstudies.11,23 The enhanced square-edged version wasthe one included in our current study. However, mea-surements at that site of the edge were not possiblewith our technique.

In summary, analysis of the microstructure of theoptic edge of currently available, square-edged hydro-philic acrylic IOLs showed a large variation in the de-viation area from a perfect square aswell as values thatwere in mean higher than previously reported valuesfor hydrophobic acrylic and silicone IOLs. This

J CATARACT REFRACT SURG -

suggests that higher rates of PCO in association withsquare-edged hydrophilic acrylic IOLs than withIOLs of other materials, as reported in some studies,may be due to edge differences instead of amaterial ef-fect. Existing and future clinical datawill help us betterunderstand the effect of microedge structure and de-sign on reducing PCO.

REFERENCES1. Buehl W, Findl O, Menapace R, Rainer G, Sacu S, Kiss B,

Petternel V, Georgopoulos M. Effect of an acrylic intraocular

lens with a sharp posterior optic edge on posterior capsule opa-

cification. J Cataract Refract Surg 2002; 28:1105–1111

2. Auffarth GU, Golescu A, Becker KA, Volcker HE. Quantification

of posterior capsule opacification with round and sharp edge in-

traocular lenses. Ophthalmology 2003; 110:772–780

3. Nixon DR. In vivo digital imaging of the square-edged barrier ef-

fect of a silicone intraocular lens. J Cataract Refract Surg 2004;

30:2574–2584

4. Buehl W, Menapace R, Findl O, Neumayer T, Bolz M, Prinz A.

Long-term effect of optic edge design in a silicone intraocular

lens on posterior capsule opacification. Am J Ophthalmol

2007; 143:913–919

5. Kohnen T, Fabian E, Gerl R, Hunold W, Hutz W, Strobel J,

Hoyer H, Mester U. Optic edge design as long-term factor for

posterior capsular opacification rates. Ophthalmology 2008;

115:1308–1314

6. Tetz M, Wildeck A. Evaluating and defining the sharpness of in-

traocular lenses; part 1: influence of optic design on the growth of

the lens epithelial cells in vitro. J Cataract Refract Surg 2005;

31:2172–2179

7. Tetz MR, Auffarth GU, Sperker M, Blum M, Volcker HE. Photo-

graphic image analysis system of posterior capsule opacifica-

tion. J Cataract Refract Surg 1997; 23:1515–1520

VOL 35, MARCH 2009

565LABORATORY SCIENCE: MICROEDGE STRUCTURE OF SQUARE-EDGED HYDROPHILIC IOLs

Figure 8. The ESEM photographs(�100 or �250) showing the sitesof area measurement (arrows) inIOLs exhibiting edges with particu-lar characteristics. A and B: Overallaspect of the edge of IOLs 11 and12. C and D: Overall aspect of theedge of IOLs 28, 29, 30, and 31. Eand F: Overall aspect of the edgeof IOLs 41 and 42.

8. Werner L, Muller M, Tetz M. Evaluating and defining the sharp-

ness of intraocular lenses; microedge structure of commercially

available square-edged hydrophobic lenses. J Cataract Refract

Surg 2008; 34:310–317

9. Brown NAP, Bron AJ. An estimate of the human lens epithelial

cell size in vivo. Exp Eye Res 1987; 44:899–906

10. Peng Q, Visessook N, Apple DJ, Pandey SK, Werner L,

Escobar-Gomez M, Schoderbek R, Solomon KD, Guindi A.

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

11. Werner L, Mamalis N, Pandey SK, Izak AM, Nilson CD,

Davis BL, Weight C, Apple DJ. Posterior capsule opacification

in rabbit eyes implanted with hydrophilic acrylic intraocular

lenses with enhanced square edge. J Cataract Refract Surg

2004; 30:2403–2409

12. Nishi O, Nishi K. Preventing posterior capsule opacification by

creating a discontinuous sharp bend in the capsule. J Cataract

Refract Surg 1999; 25:521–526

13. Nishi O, Yamamoto N, Nishi K, Nishi Y. Contact inhibition of

migrating lens epithelial cells at the capsular bend created

J CATARACT REFRACT SUR

by a sharp-edged intraocular lens after cataract surgery. J Cat-

aract Refract Surg 2007; 33:1065–1070

14. Bhermi GS, Spalton DJ, El-Osta AAR, Marshall J. Failure of

a discontinuous bend to prevent lens epithelial cell migration in

vitro. J Cataract Refract Surg 2002; 28:1256–1261

15. Boyce JF, Bhermi GS, Spalton DJ, El-Osta AR. Mathematic

modeling of the forces between an intraocular lens and the cap-

sule. J Cataract Refract Surg 2002; 28:1853–1859

16. Nanavaty MA, Spalton DJ, Boyce J, Brain A, Marshall J. Edge

profile of commercially available square-edged intraocular

lenses. J Cataract Refract Surg 2008; 34:677–686

17. Kugelberg M, Wejde G, Jayaram H, Zetterstrom C. Posterior

capsule opacification after implantation of a hydrophilic or

a hydrophobic acrylic intraocular lens; one-year follow-up. J Cat-

aract Refract Surg 2006; 32:1627–1631

18. Bender L, Spalton DJ, Uyanonvara B, Boyce J, Heatley C,

Jose R, Khan J. POCOman: new system for quantifying poste-

rior capsule opacification. J Cataract Refract Surg 2004;

30:2058–2063

19. Kugelberg M, Wejde G, Jayaram H, Zetterstrom C. Two-year

follow-up of posterior capsule opacification after implantation

G - VOL 35, MARCH 2009

566 LABORATORY SCIENCE: MICROEDGE STRUCTURE OF SQUARE-EDGED HYDROPHILIC IOLs

of a hydrophilic or hydrophobic acrylic intraocular lens. Acta

Ophthalmol (Oxf) 2008; 86:533–536

20. Richter-Mueksch S, Kahraman G, Amon M, Schild-

Burggasser G, Schauersberger J, Abela-Formanek C. Uveal

and capsular biocompatibility after implantation of sharp-edged

hydrophilic acrylic, hydrophobic acrylic, and silicone intraocular

lenses in eyes with pseudoexfoliation syndrome. J Cataract Re-

fract Surg 2007; 33:1414–1418

21. Cheng J-W, Wei R-L, Cai J-P, Xi G-L, Zhu H, Li Y, Ma X-Y.

Efficacy of different intraocular lens materials and optic edge

designs in preventing posterior capsular opacification: a meta-

analysis. Am J Ophthalmol 2007; 143:428–436

22. Heatley CJ, Spalton DJ, Kumar A, Jose R, Boyce J, Bender LE.

Comparison of posterior capsule opacification rates between

hydrophilic and hydrophobic single-piece acrylic intraocular

lenses. J Cataract Refract Surg 2005; 31:718–724

J CATARACT REFRACT SURG

23. Nishi Y, Rabsilber TM, Limberger I-J, Reuland AJ, Auffarth GU.

Influence of 360-degree enhanced optic edge design of a hydro-

philic acrylic intraocular lens on posterior capsule opacification.

J Cataract Refract Surg 2007; 33:227–231

First author:Liliana Werner, MD, PhD

Berlin Eye Research Institute, Berlin,Germany, and John A. Moran EyeCenter, University of Utah, Salt LakeCity, Utah, USA

- VOL 35, MARCH 2009