Failure of a discontinuous bend to prevent lens epithelial cell migration in vitro

Intraocular Lenses: Overview of Designs, Materials, and Pathophysiologic Features

This article provides an overview of intraocular lenses (IOLs) currently used in cataract surgery. Aspects presented include design features related to IOL construction and sites of fixation; optic, filter, and haptic materials; as well as pathophysiologic features of uveal biocompatibility, capsular biocompatibility, and postoperative IOL opacification. This overview also includes supplementary (add-on; piggyback) lenses implanted in eyes that are already pseudophakic and considerations on IOLs used in the pediatric population. Different IOLs are made available to surgeons each year, including lenses with increasingly complex design characteristics owing to advancements in manufacturing and surgical techniques.

Edge profile of commercially available square-edged intraocular lenses: Part 2

PURPOSE

To analyze the sharpness of the posterior optic edge and edge thickness of intraocular lenses (IOLs) marketed with a square-edged profile.

SETTING

University of Brighton and Brighton and Sussex University Hospitals NHS Trust, Brighton, England.

DESIGN

Laboratory study.

METHODS

Fourteen square-edged 20.0 diopter IOLs were analyzed, including 9 hydrophobic IOLs (AF-1, AF-1 iSert, Clareon, EyeCee One Crystal, CT Lucia, Envista, EyeCee One, Vivinex iSert, and RayOne Hydrophobic) and 5 hydrophilic IOLs (Asphira, CT Asphina, Incise, Synthesis, and RayOne Hydrophilic). All the IOLs were scanned following a previously published standardized technique using environmental scanning electron microscopy. The posterior optic edges were scanned at a magnification of ×500 and ×200 to measure the radius of curvature of the posterior optic edges and the optic edge thickness.

RESULTS

The radius of curvature of the posterior optic edges ranged from 4.6 to 20.6 μm. Except for the Incise IOL (7.7 μm), all hydrophilic IOLs (Synthesis [10.6 μm], Asphira [13.7 μm], RayOne Hydrophilic [14.0 μm], CT Asphina [13.7 μm]) had a radius of curvature greater than 10.0 μm. For the hydrophobic IOLs, the radius of curvature was less than 10.0 μm for the Clareon (7.9 μm), EyeCee One Crystal (4.7 μm), Vivinex iSert (7.6 μm), and CT Lucia (4.6 μm), and greater than 10.0 μm for the Envista (19.7 μm), EyeCee One (13.7 μm), AF-1 iSert (19.7 μm), AF-1 (19.7 μm) and the RayOne Hydrophobic (20.6 μm). The Vivinex iSert (150.5 μm) and the Incise (218.2 μm) were the thinnest IOLs, and the RayOne Hydrophobic (375.8 μm) and RayOne Hydrophilic IOLs (477.1 μm) were the thickest of the hydrophobic and hydrophilic IOLs, respectively.

CONCLUSIONS

Commercially marketed square-edged IOLs still differed in the sharpness of the posterior optic edge. More hydrophobic IOLs have rounder edges than those studied 10 years ago. Variations in the edge profile of hydrophobic IOLs were greater compared with the hydrophilic IOLs.

Prevention of postoperative capsular bag opacification using intraocular lenses and endocapsular devices maintaining an open or expanded capsular bag

Postoperative capsule opacification is a multifactorial physiological consequence of cataract surgery that remains the most common complication of this procedure. A literature review that included several intraocular lenses (IOLs) and endocapsular devices studied in our laboratory found that devices maintaining the capsular bag in an open or expanded state were associated with improved bag clarity. This observed effect likely occurs secondary to the complex interactions of myriad mechanisms, which include formation of a barrier to lens epithelial cell (LEC) migration, mechanical compression of residual LECs, mechanical stretch at the level of the capsule equator, maintenance of overall bag contour, and enhanced endocapsular circulation of aqueous humor. We review the designs of endocapsular devices and IOLs that minimize the degree of postoperative capsule opacification by preventing capsular bag collapse and discuss the underlying mechanisms that contribute to this phenomenon.

FINANCIAL DISCLOSURE

None of the authors has a financial or proprietary interest in any material or method mentioned.

Evaluating and defining the sharpness of intraocular lenses: microedge structure of commercially available square-edged hydrophilic intraocular lenses

PURPOSE

To evaluate the microstructure of the edges of currently available hydrophilic acrylic intraocular lenses (IOLs) in terms of their deviation from an "ideal" square as a follow-up of preliminary in vitro studies of experimental poly(methyl methacrylate) IOLs and commercially available foldable hydrophobic IOLs.

SETTING

Berlin Eye Research Institute, Berlin, Germany.

METHODS

Twenty-four designs of hydrophilic acrylic IOLs were used in this study. For each design, a +20.0 diopter (D) IOL and a +0.0 D IOL (or the lowest available plus dioptric power) were evaluated. The IOL edge was imaged under low-vacuum (0.7 torr), high-magnification scanning 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 of deviation from a perfect square ranging from 60.84 to 871.51 microm(2) for the +20.0 D IOLs and from 35.52 to 826.55 microm(2) for the low-diopter IOLs. Although some differences in edge finishing between the IOLs analyzed were observed, edge surfaces of hydrophilic acrylic IOLs appeared overall smooth under environmental SEM.

CONCLUSIONS

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

Prevention of lens epithelial cell growth in vitro using mibefradil-containing PLGA micro particles

The prevention of the posterior capsule opacification is still unsolved. To interfere with proliferating cells the T-type calcium channel antagonist Mibefradil was immobilized in poly-lactic-co-glycolic-acid micro particles which were fixed at a capsular tension ring and tested in a human organ culture model as well as in human lens cells HLE-B3 in vitro. It is feasible to get a release significantly affecting cell viability and growth evaluated by MTT test and cell cycle analysis. In addition, Bionas^® sensor chips were used for time-dependent adhesion experiments in living lens cells. Interestingly, the concentration of Mibefradil which inhibited subconfluent cells is not effective in confluent cells. This is an important feature for the protection of the intact tissue in the eye.

Edge profile of commercially available square-edged intraocular lenses

PURPOSE

To analyze the sharpness of the posterior optic edge profile and edge thickness of intraocular lenses (IOLs) marketed with a square-edged profile.

SETTING

Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom.

METHODS

Seventeen square-edged 20.0 diopter IOLs of different manufacture, design, and material were selected. After the environmental scanning electron microscopy technique was standardized, repeatability of the technique was tested. Posterior optic edges of all IOLs were scanned at a magnification of x 500. Local radii of curvature of the posterior optic edges were measured by purpose-designed software. Optic edge thickness was also measured from the electron micrographs.

RESULTS

The repeatability of the scanning technique was excellent (+/-0.10 microm). The radius of curvature of posterior optic edges ranged from 7.6 to 23.1 microm. Hydrophilic acrylic IOLs (except the HumanOptics MC Microlens 611 MI-B and 1CU) had radii of curvatures more than 10.0 microm of the posterior optic edge compared with hydrophobic acrylic and silicone IOLs (<10.0 microm) except the Hoya AF-1 (19.9 microm). Alcon AcrySof single-piece (SN60WF), HumanOptics 1CU, and AMO Clariflex CLRFLXC IOLs had the thinnest optic edges in the hydrophobic, hydrophilic, and silicone groups, respectively.

CONCLUSIONS

Commercially marketed square-edged IOLs differed in the sharpness of the posterior optic edge. Hydrophobic acrylic and silicone IOLs have sharper posterior optic square edge than most hydrophilic acrylic IOLs. This probably reflects difference in manufacturing techniques. Differences in posterior optic edge profile may explain variation in posterior capsule opacification performance with different IOLs and materials.

Contact inhibition of migrating lens epithelial cells at the capsular bend created by a sharp-edged intraocular lens after cataract surgery

PURPOSE

To investigate whether the lens epithelial cells (LECs) at the capsular bend created by a sharp-edged intraocular lens (IOL) are in the G(0) phase of the cell cycle.

SETTING

Nishi Eye Hospital, Osaka, Japan.

METHOD

A CeeOn Edge silicone IOL (AMO) with sharp edges was implanted in 1 eye and a PhacoFlex II silicone IOL (AMO) with rounded edges in the contralateral eye after standard cataract surgery in 6 rabbits. Immunohistochemical staining for the Ki-67 antibody was performed 1 day, 3, 4, and 7 weeks after surgery.

RESULTS

In eyes with the sharp-edged IOL, LECs with thin, elongated nuclei accumulated at, but did not extend beyond, the capsular bend and stained negative for the Ki-67 antibody, indicating that they were in the G(0) phase of the cell cycle. In contrast, in the eye with the round-edged IOL, continuous migration of a predominantly monolayer of LECs over the IOL and onto the posterior capsule occurred. These cells were Ki-67 positive, indicating that they were proliferating.

CONCLUSIONS

Lens epithelial cells at the capsular bend of sharp-edged IOLs were in the G(0) phase of the cell cycle, indicating that they were contact inhibited. These findings support the theory the sharp posterior optic edge of the IOL inhibits LEC migration, reducing formation of posterior capsule opacification. Whether these LECs can reactivate when the capsular bend is eliminated by later formation of a Soemmerring's ring requires further studies.

Fellow-eye comparison of posterior capsule opacification rates after implantation of 1CU accommodating and AcrySof MA30 monofocal intraocular lenses

PURPOSE

To measure posterior capsule opacification (PCO) and neodymium:YAG (Nd:YAG) capsulotomy rates between the AcrySof MA30 intraocular lens (IOL) (Alcon) and the 1CU IOL (HumanOptics) in a fellow-eye comparison.

SETTING

Ophthalmology Department, St. Thomas' Hospital, London, United Kingdom.

METHODS

Thirty patients who had bilateral cataract surgery with a 1CU IOL prospectively randomly allocated to 1 eye and an AcrySof MA30 monofocal IOL to the other eye were examined. Best corrected distance visual acuity was recorded using the Early Treatment Diabetic Retinopathy Study logMAR chart. Digital retroillumination images of the posterior capsule were taken with the pupil dilated and analyzed with POCO software.

RESULTS

Eyes with the 1CU IOL had significantly higher PCO rates than eyes with the MA30 IOL at all time points. By 2 years after surgery, 50% of eyes with a 1CU IOL had required Nd:YAG capsulotomy compared with no eyes with an MA30 IOL. There was no significant difference in visual acuity at any time point when post Nd:YAG capsulotomy was taken in to account.

CONCLUSIONS

The 1CU IOL has 4 broad optic-haptic junctions where the square-edged barrier is breached; this appeared to allow passage of lens epithelial cells, leading to an increase in PCO. However, the increased PCO cannot be attributed to this alone as the 1CU is hydrophilic, a factor known to be associated with higher PCO rates.

[After-cataract following intraocular lens implantation. Part I. Genesis and prevention by optimizing conventional lens implants and surgical techniques]

After-cataract is the most common complication in cataract surgery. Implementing a sharp posterior optic edge has, together with improved cortical aspiration, drastically reduced its rate. The impact of optic design and material has been systematically studied in detail in Vienna in a series of prospectively randomized intra-individual comparison studies using objective evaluation methods. Circular rhexis-optic overlap is essential for the durability of the posterior sharp optic edge barrier effect. Using haptics with a capsular bag design and a slim junction to the optic enhanced it further. The use of fibrosis-inducing optic materials has been shown to prolong the barrier effect, which was decreased after anterior capsule polishing. Although the incidence of clinically significant after-cataract has been significantly reduced by these conventional measures, it still cannot be completely avoided.

Routine posterior optic buttonholing for eradication of posterior capsule opacification in adults: report of 500 consecutive cases

PURPOSE

To study the efficacy of posterior optic buttonholing (POBH) through a primary posterior capsulorhexis (PPCCC) to preserve full capsular transparency, and its potential as a routine alternative to standard in-the-bag implantation of sharp-edged optic intraocular lenses (IOLs).

SETTING

Department of Ophthalmology, Medical University of Vienna, Vienna, Austria.

METHODS

After standard cataract removal, a PPCCC 4.0 to 5.0 mm in diameter was performed and the optic of a 3-piece IOL buttonholed posteriorly. One third of the eyes additionally had extensive anterior capsule polishing. All surgeries were performed under topical anesthesia.

RESULTS

The first 500 consecutive surgeries were evaluated. In 11 eyes, POBH was not performed as planned. In 4 cases, anterior capsulorhexis fixation of the optic was used as an alternative. In the early series, vitreous entanglement was seen in 5 eyes, of which 1 case prompted translimbal anterior vitrectomy. No case of cystoid macula edema was observed. One case of peripheral retinal detachment in a highly-myopic eye 4 months postoperatively appeared to be unrelated to the surgery. All lenses were well-centered without tilt, and both capsule leaves remained clear especially after additional polishing.

CONCLUSION

Posterior optic buttonholing precludes lens epithelial cells from accessing the retrolental space. The sandwiched posterior capsule blocks optic contact and thus fibrosis of the anterior capsule. Posterior optic buttonholing avoids after-cataract independent of optic edge design. Anterior capsule polishing adds to its efficacy by excluding any residual fibrosis. Surgery under topical anesthesia was well-controlled and safe. Posterior optic buttonholing may become a routine alternative to standard in-the-bag IOL implantation when supported by a longer follow-up.

Posterior capsule opacification

PURPOSE OF REVIEW

This paper assesses the factors that contribute to the formation of an effective capsular bend as a deterrent to posterior capsule opacification. Its goal is to assist the practicing ophthalmologist in separating current understanding of this process from various working models previously proposed.

RECENT FINDINGS

While a square-edge design appreciably improves resistance to posterior capsule opacification, significant factors remain under the control of the surgeon. These factors combine to form the physical and psychological barrier of a capsular bend. Innovative digital imaging has shown lens epithelial cell migration, allowing for a more rapid assessment of posterior capsule opacification resistance. A three-piece intraocular lens allows for full 360 degree capsular bend formation surrounding the optic edge; some single-piece designs may inhibit capsular bend formation. Decreasing, but not eliminating, the surviving lens epithelial cell population may diminish capsular bend strength, which may decrease resistance to posterior capsule opacification in the face of a regenerating cortex. All demographic features of clear/refractive lens exchange suggest higher rates of posterior capsule opacification than with standard cataract surgery.

SUMMARY

The quality of capsular bend formation will determine how resistant an intraocular lens will be to posterior capsule opacification as a consequence of regenerating cortex. As refractive lens exchange and new accommodating intraocular lens designs become more popular, the problems of regenerating cortex will increase in magnitude.

Long-term Effect of Sharp Optic Edges of a Polymethyl Methacrylate Intraocular Lens on Posterior Capsule Opacification

PURPOSE

To compare the posterior capsule opacification (PCO) inhibiting effect of a 3-piece polymethyl methacrylate (PMMA) intraocular lens (IOL) with a sharp optic edge design with that of the round-edged version of the same IOL during a 5-year period.

DESIGN

Randomized patient- and examiner-masked clinical trial with intraindividual comparison.

PARTICIPANTS

Thirty-two patients with bilateral age-related cataract (64 eyes).

METHODS

Each study patient had phacoemulsification cataract surgery in both eyes and received a sharp optic edge PMMA IOL in one eye and a round optic edge PMMA IOL in the fellow eye (both by Dr Schmidt in Germany). Follow-up examinations were at 1 week, 1 month, 1 year, 3 years, and 5 years. Digital retroillumination images were taken from each eye. The amount of posterior capsule opacification was assessed objectively by means of automated image analysis software (Automated Quantification of After-Cataract) at 1 year, 3 years, and 5 years after surgery.

MAIN OUTCOME MEASURE

Posterior capsule opacification score: 0-10.

RESULTS

The sharp optic edge IOL showed significantly less regeneratory and fibrotic PCO at 1 year, 3 years, and 5 years after surgery. The mean AQUA PCO score was 5.12 for the round-edge and 2.49 for the sharp-edge IOL (scale, 0-10; P<0.001) at 5 years. The mean difference among patients for the PCO score in the eye implanted with the sharp optic edge versus the score in the eye with the round optic edge was 2.83 at 5 years (95% confidence interval, 1.66-4.00). Due to the large number of neodymium:yttrium-aluminum-garnet laser capsulotomies that were performed (12 in the round-edge group and 4 in the sharp-edge group), there was no significant difference in visual acuity between both groups at any time point.

CONCLUSIONS

Compared with the round-edge version, the sharp optic edge design of a 3-piece PMMA IOL led to significantly less PCO at 1 year, 3 years, and 5 years after surgery. However, the sharp optic edge did not lead to complete PCO prevention during this follow-up period. This finding has implications for the design of PMMA IOLs used for cataract surgery, especially in the developing world.

Evaluating and defining the sharpness of intraocular lenses

PURPOSE

To develop a new method for the evaluation of the optic edge design of intraocular lenses (IOLs).

SETTING

Charité Humboldt University and Berlin Eye Research Institute (Beri), Berlin, Germany.

METHODS

Poly(methyl methacrylate) IOLs with 11 edge designs were manufactured. Each lens design was evaluated using EPCO 2000. Also, edge's ability to stop cell growth was observed by placing each IOL into cell culture and observing cell growth over 18 days on average.

RESULTS

Only 3 groups, those with the sharpest edge design, prevented the growth of lens epithelial cells onto the visual axis of the lens. The edge design that effectively stopped cell growth was characterized by an area above the edge of 13.5 microm2 at the most.

CONCLUSION

Results shows that the edge design of IOLs plays an important role in the prevention of posterior capsule opacification. A specific optic edge design was most effective in this prevention.

[Influence of intraocular lens material and design on the development of posterior capsule opacification]

Based on the literature of 1999-2005, we attempted to clarify the influence of material and design of an intraocular lens (IOL) on the development of posterior capsule opacification (PCO) and identify the future problems to be solved. The sharp edge design of an IOL has significantly reduced PCO in recent years. Histopathological studies showed that a sharp capsular bend was formed at the sharp posterior optic edge, and the migration of lens epithelial cells was obviously inhibited at the site. Experimental and clinical studies suggest that the sharper the edge is, the sharper the capsular bend, and the greater the preventive effect, regardless of IOL material. The sharp capsule bend appears to represent a physical hindrance, which may induce contact inhibition of cell movement. How material participates in the preventive effect should be clarified in a future study. Thus, at the moment, the formation of capsular bend at the posterior optic edge appears to be the decisive criterion to evaluate the influence of IOL material and design on the development of PCO. Optimization of design and material of an IOL, which facilitates capsular bend formation as sharply and quickly as possible, may reduce PCO to a clinically negligible level.

Posterior capsule opacification in rabbit eyes implanted with 1-piece and 3-piece hydrophobic acrylic intraocular lenses

PURPOSE

To evaluate the outcome of posterior capsule opacification (PCO) after implantation in rabbit eyes of currently available 3-piece and 1-piece hydrophobic acrylic intraocular lenses (IOLs) with square optic edges.

SETTING

John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA.

METHODS

The 3-piece designs evaluated were the AR40e (Advanced Medical Optics Inc.) and the MA60AC (Alcon, Inc.); the 1-piece designs were the SA60AT and the SA30AT (Alcon, Inc.). Nine lenses of each type were implanted in a randomized manner by the same surgeon in 18 Dutch Belted pigmented rabbits. After a follow-up of 3 weeks, the rabbits were killed and analyses of the enucleated eyes were performed from the posterior or Miyake-Apple view. The intensity of central PCO, peripheral PCO, and Soemmering's ring formation was scored from 0 to 4. The area of Soemmering's ring formation was also scored from 0 to 4 based on the number of quadrants involved. Other parameters analyzed were capsulorhexis coverage of the IOL anterior surface, IOL centration, fixation, and presence of striae. Results from the posterior view were complemented by histopathologic evaluation of the eyes.

RESULTS

No statistically significant difference was found between the 4 groups of IOLs in the parameters analyzed from the posterior view. When cell ingrowth occurred with the 1-piece designs, causing peripheral and central PCO formation, it was more likely to start at the optic-haptic junctions, as observed during the clinical follow-up with slitlamp examination and confirmed by gross and histopathologic analyses of the enucleated eyes.

CONCLUSIONS

The square, truncated optic edge is the most important IOL design feature for PCO prevention. The optic-haptic junctions of the 1-piece designs appear to be sites where the barrier effect of the truncated optic edge is less effective.

Long-term efficacy of adding a sharp posterior optic edge to a three-piece silicone intraocular lens on capsule opacification: five-year results of a randomized study

PURPOSE

To compare the intensity of capsule opacification with the sharp and the round optic edge variant of an open-loop hydrophobic silicone intraocular lens (IOL).

DESIGN

Randomized, controlled, double-blind clinical trial with intraindividual comparison.

METHODS

Fifty-one patients with bilateral age-related cataract were included (102 eyes). Each patient had had cataract surgery in both eyes and received a Microsil IOL with a sharp optic edge design (model S) in one eye and a Microsil IOL with a round optic edge design (model R) in the fellow eye. Both IOLs had an identical haptic design (nonangulated polymethylmethacrylate) and silicone optic material. The patients were examined at the slit lamp, best-corrected visual acuity was assessed, and standardized high-resolution digital retroillumination images of the posterior capsule were taken 5 years after surgery. The intensity of regeneratory posterior capsule opacification (rPCO), fibrotic PCO (fPCO), and anterior capsule opacification (ACO) was assessed subjectively at the slit lamp, and of rPCO, objectively using automated image analysis software (AQUA). The need for an Nd:YAG laser capsulotomy (Nd:YAG-LCT) was noted.

RESULTS

The mean AQUA PCO score was 1.2 for the model S and 2.4 for the model R lens (P = .001). The model S lens also led to less peripheral fPCO (P = .003). Concerning ACO, there was no significant difference between both IOL groups (P = .72). Whereas no capsulotomy was required with the model S, four cases (16%) had been performed in the model R group.

CONCLUSION

Five years postoperatively, the sharp-edged silicone IOL showed less rPCO and fPCO than the round-edged IOL. However, regarding ACO, there was no significant difference between both IOL styles.

Comparison of posterior capsule opacification rates between hydrophilic and hydrophobic single-piece acrylic intraocular lenses

PURPOSE

To determine the effect of intraocular lens (IOL) material on the development of posterior capsule opacification (PCO) at 1 year.

SETTING

Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom.

METHODS

One hundred six eyes of 53 patients with bilateral cataract and no other ocular comorbidity were prospectively randomized to receive a hydrophobic acrylic or hydrophilic acrylic single-piece IOL in the first eye to have surgery. The alternate IOL was implanted in the fellow eye 4 to 6 weeks later. All surgery was performed by a single surgeon. Postoperative follow-up was 1 day, 1 and 6 months, and 1 year. At each visit, the best corrected high- and low-contrast visual acuities were assessed and a high-intensity digital retroillumination photograph was taken. Posterior capsule opacification was assessed from the digital images by a single operator using a dedicated software program and calculated as the percentage area of opacified capsule.

RESULTS

One year postoperatively, the median percentage area of PCO was 50.3% in the hydrophilic IOL group and 4.9% in the hydrophobic IOL group (P<.001). The difference in PCO was not accounted for by loss of contact between the capsulorhexis and IOL surface. Further analysis showed that lens epithelial cells tended to invade the posterior capsule at the haptic-optic junction. This was more marked in the hydrophilic IOL group.

CONCLUSIONS

The rate of PCO was significantly higher with the hydrophilic IOL. However, the results cannot be attributed to the IOL material alone as they show the importance of both IOL material and design.

Three-year follow-up of posterior capsule opacification with two different silicone intraocular lenses

PURPOSE

To compare posterior capsule opacification (PCO) after cataract surgery with implantation of two silicone intraocular lenses (IOLs) with different designs.

METHODS

We carried out a prospective, clinical study of 116 patients randomized to standardized phacoemulsification with implantation of CeeOn Edge (n = 57) or SI40NB (n = 59) IOLs. The follow-up period was 3 years. To evaluate PCO morphologically, digital images were obtained and analysed using evaluation of posterior capsule opacification computer software (epco). The neodymium:YAG (Nd:YAG) capsulotomy rate was recorded.

RESULTS

At 2 and 3 years, the eyes with SI40NB IOLs had significantly more PCO than those with the CeeOn Edge IOLs (p = 0.00014 and p = 0.002). Nine Nd:YAG capsulotomies were performed in the SI40NB group and none in the CeeOn Edge group. This difference was statistically significant (p = 0.003). In some patients a regression of PCO was noticed and confirmed using epco. Statistically less PCO was noted when the capsulorhexis rim was placed so that it covered all 360 degrees of the optic of the IOL.

CONCLUSIONS

A clinically and statistically significant difference in PCO development between CeeOn Edge and SI40NB IOLs at 2 and 3 years postoperatively was found. These findings support earlier studies indicating that a sharp edge of the optic is a more important factor in IOL design than IOL material in the prevention of PCO.

Anterior capsule relationship of the AcryS of intraocular lens optic and posterior capsule opacification

OBJECTIVE

To evaluate the relationship of the anterior capsule and the AcrySof MA30BA intraocular lens (IOL) and its impact on the development of central posterior capsule opacification (PCO).

DESIGN

Prospective, randomized, controlled trial.

PARTICIPANTS

Two hundred two patients with senile cataracts received an AcrySof IOL between July and December 1998 at Iladevi Cataract and IOL Research Center, Ahmedabad, India.

INTERVENTION

Patients were randomized prospectively to receive 1 of the 3 possibilities of anterior capsule and IOL optic relationship: group 1, total anterior capsule cover (360 degrees ) of the optic; group 2, no anterior capsule cover (360 degrees ) of the optic; group 3, partial anterior capsule cover (<360 degrees ) of the optic. After surgery, slit-lamp video photography was performed every 6 months for 3 years. Analyses of variance and chi-square tests were used to compare treatment groups.

MAIN OUTCOME MEASURES

Incidence of PCO in the 3 groups. The posterior capsule was divided into 3 zones: peripheral, central 3 mm, and midperipheral (the space between the peripheral and the central zones).

RESULTS

The average follow-up was 35.3 +/- 1.52 months in all the groups. At 3 years, the rate of central PCO was 6.4% in group 1, 7.1% in group 2, and 5.9% in group 3 (P = 0.9). Midperipheral PCO was present in 24.2% in group 1, 16% in group 2, and 20.6% in group 3 (P = 0.9). Peripheral PCO was seen in 100% of patients in all groups. The neodynium:yttrium-aluminum-garnet laser (Nd:YAG) posterior capsulotomy rate was 0% in all groups.

CONCLUSIONS

There was no significant difference in the incidence of development of central PCO among the 3 groups. No patient experienced central PCO that required Nd:YAG capsulotomy. When using the AcrySof IOL model MA30BA, the relationship of the anterior capsule and the IOL does not seem to be a factor that relates to the development of central PCO.

Mathematical modeling of the forces between an intraocular lens and the capsule

PURPOSE

To model the pressure relationship between an intraocular lens (IOL) and the capsular bag.

SETTING

Department of Physics, Kings' College, London University, London, United Kingdom.

METHODS

A mathematical model was made of the forces between the capsule and IOL showing that the pressure related to the local radius of curvature of the IOL at any given point. The local radius of curvature for round-edged and square-edged IOLs was measured from electron micrographs of the IOL profiles, and the corresponding pressure profiles were calculated and compared.

RESULTS

The pressure between an IOL and the capsular bag was proportional to the quotient of the tension in the capsule divided by the local radius of curvature of the IOL, with a constant of proportionality that depended on the coefficient of friction between the capsule and IOL. Measuring the local radius of curvature of the 2 IOL types suggested a pressure increase of at least 69% +/- 6% at the optic edge with the square-edged IOL.

CONCLUSIONS

The mathematical model predicted that IOLs with square-edged optic profiles exerts higher pressure on the posterior capsule than IOLs with round-edged optic profiles. The higher pressure may form a physical barrier to lens epithelial cell migration onto the posterior capsule.