Loop memory of haptic materials in posterior chamber intraocular lenses

PURPOSE: To compare the shape recovery ratios after compression of haptic materials used in the manufacture of intraocular lenses (IOLs). SETTING: Center for Research on Ocular Therapeutics and Biodevices, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA. METHODS: The loop memory of 40 silicone-optic posterior chamber IOLs was studied. All the IOLs had modified-C haptics made of poly(methyl methacrylate) (PMMA; n = 10), polyimide (n = 10), polyvinylidene fluoride (PVDF; n = 10), and polypropylene (PP; n = 10). After the overall diameter of each lens was measured (day 0), the lenses were inserted into plastic wells (9.5 mm in diameter) and immersed in water (37 degrees C) for 1 month. They were then placed on an open plate and allowed to reexpand for 2 months. Overall diameter measurements were performed within 5 minutes of the IOLs' removal from the wells and at subsequent time points (days 14, 28, 30, 60, 74, 88, and 95). RESULTS: The loop memory of each lens was expressed as the difference between the initial overall diameter measurement (pretest) and the measurement at each time point; the lower the value, the higher the memory. The overall difference among the 4 groups was statistically significant at each time point (P < or = .001). From days 30 to 95, silicone-PMMA, silicone-elastimide, and silicone-PVDF IOLs had similar loop memory mean values, which were significantly lower than the mean value of silicone-PP IOLs (P <.05). The latter design tended to be deformed after removal from the wells, with increased optic-haptic angulation.CONCLUSION: Studying the loop memory of haptic materials (PMMA, polyimide, PVDF, and PP) used in the manufacture of posterior chamber IOLs can help surgeons choose an appropriate IOL for each patient.     

Comparison of the biomechanical behavior of foldable intraocular lenses

PURPOSE: To compare a standardized battery of biomechanical laboratory tests to assess the performance of popular foldable intraocular lenses (IOLs). SETTING: Biomedical testing facilities, Alcon Research, Ltd., Fort Worth, Texas, USA. METHODS: Using industry-standard biomechanical testing techniques, 1- and 3-piece foldable IOLs (Alcon AcrySof MA60BM, MA30BA, SA30AL, SA60AT; Allergan Sensar AR40, PhacoFlex II SI-40NB; Bausch & Lomb Soflex LI61U; Pharmacia & Upjohn CeeOn 920) and a 1-piece all-poly(methyl methacrylate) (PMMA) IOL (Alcon MZ30BD) were tested under identical conditions with regard to (1) tensile/elastic properties by comparing haptic pull strength and haptic elongation and (2) compression properties by comparing haptic compression forces, haptic compression force decay over time, and axial displacement. All tests were performed with the IOLs submersed in a controlled-temperature water bath (mean 35 degrees C +/- 2 degrees C [SD]). RESULTS: For all IOLs, the ultimate elongation and pull strength of the haptics before failure was highest with the Alcon SA30AL and SA60AT. Similarly, the force required to compress haptics to a prescribed 10.0 mm diameter was least with the SA30AL and the SA60AT lenses. These 1-piece lenses also showed the least decay of residual compression force as a function of time. Optic displacement along the optical axis with haptic compression to 10.0 mm was least with the Alcon 1-piece IOLs and the all-PMMA control IOL. CONCLUSION: AcrySof 1-piece SA30AL and SA60AT IOLs demonstrated superior biomechanical characteristics over other foldable IOL designs.     

Complement activation by surface modified poly(methyl methacrylate) intraocular lenses

The complement activation potential of surface modified (passivated) poly(methyl methacrylate) (PMMA) intraocular lenses (IOLs) with polypropylene loops was compared to that of standard PMMA IOLs with polypropylene loops. Both lens types were incubated in human sera for six hours and then the C3a and C5a levels were measured by radioimmunoassay. Sera incubated with either IOL type generated significantly higher levels of C3a and C5a than control sera incubated without any IOL. The amount of C3a and C5a generated by the passivated PMMA IOLs was comparable to the levels generated by the standard PMMA IOLs. The results of this study show that surface passivated PMMA IOLs with polypropylene loops activated complement to the same level as standard PMMA IOLs with polypropylene loops.     

In vitro adhesion of Pseudomonas aeruginosa and Staphylococcus aureus to surface passivated poly(methyl methacrylate) intraocular lenses.

Bacterial attachment to intraocular lenses (IOLs) can be a cause of infectious endophthalmitis following cataract surgery. In this study, Pseudomonas aeruginosa and Staphylococcus aureus adhered in vitro to untreated poly(methyl methacrylate) (PMMA) and to surface passivated PMMA lenses. The IOLs were placed in bacterial suspensions (1 x 10(7) cfu/ml) in vitro. Significantly fewer S. aureus attached (P < .05) to the normal PMMA IOLs (4,535 +/- [SD] 3,052 bacteria/mm2) and to passivated PMMA IOLs (8,720 +/- 10,040 bacteria/mm2) than did P. aeruginosa (normal PMMA: 67,808 +/- 45,070 bacteria/mm2, passivated PMMA: 85,795 +/- 70,647 bacteria/mm2). The differences in bacterial attachment to surface passivated IOLs and to untreated PMMA lenses were not significant.     

Foldable silicone versus poly(methyl methacrylate) intraocular lenses in combined phacoemulsification and trabeculectomy

PURPOSE: To compare the outcome of phacotrabeculectomy with implantation of poly(methyl methacrylate) (PMMA) or foldable silicone intraocular lenses (IOLs). METHODS: Thirty patients were randomized to receive a 5.5 mm PMMA IOL through a 5.0 mm incision or a foldable silicone IOL (Allergan SI-30) through a 3.2 mm incision. Visual acuity, intraocular pressure (IOP), bleb survival, inflammation, endothelial cell changes, and complications were examined at intervals up to 6 months. RESULTS: There was no difference between the 2 groups in final visual outcome, final IOP control, bleb survival, and endothelial cell changes. Two months after surgery, there was significantly more inflammation in the silicone IOL group than in the PMMA group (P <. 05). The silicone group had a significantly higher combined complication rate including iris capture, choroidal effusion, and epiretinal membrane formation (P <.05). CONCLUSIONS: Foldable silicone IOLs were comparable to conventional PMMA lenses in visual outcome, IOP control, bleb formation, and endothelial changes. However, some silicone lenses are associated with an increased risk of recurrence of inflammation and a higher final complication rate in combined cataract and filtration surgery.     

Implantation of IOLs with different diameters]

The intraocular lenses (IOLs) commonly used today are 13.5 to 14 mm in diameter, and this diameter is considered by some to be unnecessarily large. The size of the crystalline lens and the diagonal width between the ciliary sulcus were measured in rabbit eyes and human eyes. Then, IOLs with a smaller diameter (12.5 mm) were evaluated after implantation into rabbit eyes. The mean diameter of the human crystalline lens was 9.6 mm and its thickness was 4.1 mm. The mean width of the ciliary sulcus was 11.1 mm. The crystalline lenses of rabbits were larger than those of humans. Decentration and posterior capsular opacification score were 0.33 mm and 0.63 in 12.5 mm IOL, and 0.47 mm and 0.61 in 14.0 mm IOL. Indicating that the result of implanting the 12.5 mm IOL was not inferior to that of implanting the conventional 14 mm IOL. The average width of the ciliary sulcus is 11.1 mm, indicating that a 12.5 mm IOL is of a sufficient size to be firmly fixed in this sulcus. In addition, a 12.5 mm IOL is considered to be safer, because larger lenses may lead to erosion or vessel compression that could induce ischemia or neovascularization.     

Risk factors for anterior capsule contraction syndrome with polypropylene or poly(methyl methacrylate) haptics.

PURPOSE: To determine the effect of haptic composition on the development of anterior capsule contraction syndrome (CCS) requiring neodymium: YAG anterior capsulotomy. SETTING: Ophthalmology practice in Lancaster, Pennsylvania, USA. METHODS: This retrospective study covered a 30 month period during which 1 surgeon discontinued implanting AMO SI-30NB intraocular lenses (IOLs) with polypropylene haptics (n = 216) in favor of SI-40NB IOLs with poly(methyl methacrylate) (PMMA) haptics (n = 127). The transition was motivated by the suspicion that the PMMA haptics would maintain the capsulorhexis opening better and reduce the need for an anterior capsulotomy. RESULTS: Three eyes with SI-30NB IOLs (1.4%) required anterior capsulotomies; 2 eyes had preoperative pseudoexfoliation syndrome and required the capsulotomy within 3 months of surgery. Three eyes with SI-40NB IOLs (2.4%) required anterior capsulotomies within 4 months; 2 eyes had preoperative pseudoexfoliation syndrome and 1 had traumatic zonular weakness. The incidence of anterior capsulotomy did not differ significantly between the 2 IOL populations (P > .5), although preoperative pseudoexfoliation syndrome was a significant risk factor in both groups (P < .005). CONCLUSIONS: The polypropylene haptics of the SI-30NB IOL and the PMMA haptics of the SI-40NB IOL did not differ significantly in their ability to prevent CCS requiring anterior capsulotomy. Regardless of IOL haptic composition, eyes with preoperative zonular weakness associated with pseudoexfoliation syndrome or ocular trauma can develop CCS within 3 months of surgery and should, therefore, be followed closely in the early postoperative weeks to minimize the sequelae of anterior capsule fibrosis.     

In vitro adherence of Staphylococcus epidermidis to polymethyl methacrylate and acrysof intraocular lenses

PURPOSE: To investigate the adherence of one clinically relevant ocular isolate of Staphylococcus epidermidis to polymethyl methacrylate (PMMA) and Acrysof (Alcon Surgical, Fort Worth, TX) intraocular lenses (IOLs). DESIGN: Experimental study. PARTICIPANTS: The authors examined the in vitro adherence of one clinically relevant ocular isolate of S. epidermidis. Adherence was tested on 12 PMMA IOLs and 12 Acrysof IOLs. METHODS: Six IOLs (three of each type) were placed in different test tubes containing bacterial suspension (10(8) cfu/ml) and incubated at 37 degrees C. At different times (3 minutes, 30 minutes, and 90 minutes), each IOL type was removed from the test tube, rinsed in sterile phosphate-buffered saline, and transferred into sterile brain-heart infusion broth. The broth with the IOL was sonicated on low power for 3 minutes to remove adhered bacteria. Two serial 10-fold dilutions of the broth containing the dislodged bacteria were plated on mannitol agar plates. The plates were incubated overnight at 37 degrees C and then bacterial colonies were counted. All assays were performed in triplicate. Additional lenses (three of each type) were incubated with S. epidermidis for different times (3 minutes, 30 minutes, and 90 minutes) and then examined with scanning electron microscopy. MAIN OUTCOME MEASURES: The number of adhered bacteria per area (mm ) of IOL optic was calculated. Statistical analysis included calculation of arithmetic means and 95% confidence intervals (t test). RESULTS: Direct counting of viable adherent bacteria released by sonication showed that the amount of adhered bacteria per area of IOL optic after 3, 30, and 90 minutes' incubation in S. epidermidis suspension was 0.1 x 10(2)/mm2, 3.6 x 10(2)/mm2, and 11 x 10(2)/mm2 (PMMA IOLs), and 4.4 x 10(2)/mm2, 3.1 x 10(2)/mm2, and 2.3 x 10(2)/mm2 (Acrysof IOLs). Direct counting of adherent bacteria in scanning electron microscopy photographs revealed that the total amount of adhered bacteria per area of IOL optic after 3, 30, and 90 minutes' incubation in S. epidermidis suspension was 1.1 x 10(2)/mm2, 4.4 x 10(2)/mm2, and 5.5 x 10(2)/mm2 (PMMA IOLs) and 13 x 10(2)/mm2, 33.9 x 10(2)/mm2, and 72 x 10(2)/mm2 (Acrysof IOLs). CONCLUSIONS: Results suggest that in vitro adherence of S. epidermidis to IOLs is influenced by IOL materials. After 3 minutes' incubation, Acrysof IOLs appeared to be more permissive to S. epidermidis adherence than PMMA IOLs. The difference was statistically significant (P < 0.05). However, at 90 minutes, Acrysof IOLs had a lower viable bacterial count than did the PMMA IOLs. Bacterial adherence appeared to be greater in areas with surface irregularities. Adherence of S. epidermidis to IOLs may play a role in the pathogenesis of some forms of endophthalmitis after cataract surgery.     

Bacterial adhesion to rigid and foldable posterior chamber intraocular lenses: in vitro study

PURPOSE: To determine the in vitro bacterial adherence to intraocular lenses (IOLs) routinely used at 1 center. SETTING: University Hospital of Vienna, Vienna, Austria. METHODS: Four types of rigid IOLs (hydrophobic poly[methyl methacrylate] [PMMA] and hydrophilic heparin-surface-modified PMMA) and 5 types of foldable intraocular lenses (hydrophobic silicone, hydrophobic acrylic, and hydrophilic acrylic) were used in the experiment. Under standardized conditions, the IOLs were contaminated with 2 strains of Staphylococcus epidermidis. A sonication method and impression method were used for quantification. The mean bacterial density per lens type (colony forming units/mm(2)) was compared. RESULTS: With both germs and both quantification methods, more bacteria was found on hydrophobic lenses than on IOLs with hydrophilic surfaces (P =.001). The Alcon AcrySof and Askin UV80F IOLs had the greatest and the Corneal Acrygel and Bausch & Lomb Hydroview IOLs the least affinity to these microorganisms. CONCLUSION: The data suggest that hydrophilic IOLs can help reduce the rate of postoperative endophthalmitis as a result of their surface properties.     

In vitro adhesion of Staphylococcus epidermidis to intraocular lenses

PURPOSE: To compare the in vitro adherence of slime-producing and non-slime-producing Staphylococcus epidermidis to different intraocular lenses (IOLs) to study the organism's contribution to postoperative endophthalmitis. METHODS: Strains of slime-positive (ATCC 35984) and slime-negative (ATCC 12228) S epidermidis were used. The IOLs were made of poly(methyl methacrylate) (PMMA), PMMA with polypropylene haptics, silicone, hydrogel, acrylic, heparin-surface-modified (HSM) PMMA, and fluorine-surface-modified PMMA. The lenses were incubated overnight with bacteria, then sonicated and vortexed to separate the adhered bacteria. Quantitative cultures were performed and the results statistically analyzed. RESULTS: Slime-negative strains of S epidermidis adhered to all IOLs but at a lower level than slime-positive strains. The most adherent lenses were acrylic with the positive strain and PMMA with the negative strain. The least adherent IOLs were PMMA with the positive strain and hydrogel with the negative strain. There were no significant differences between rigid and foldable lenses. Polypropylene was significantly more adherent than PMMA to the slime-positive strain. The acrylic and the HSM PMMA IOLs were significantly more adherent to the positive strain. CONCLUSIONS: In vitro, there were significant differences in bacterial adhesion among IOL materials. Slime-positive strains of S epidermidis were more adherent than slime-negative ones.