Ultrastructural investigation demonstrating reduced cell adhesion on heparin-surface-modified intraocular lenses

Physicochemical and surface properties of acrylic intraocular lenses and their clinical significance

To analyze and compare several commercially available acrylic intraocular lenses (IOLs) with particular regard to their clinical significance, we examined the physicochemical and surface properties of four currently available acrylic IOLs using static water contact angle, atomic force microscopy (AFM), Raman spectroscopy, and differential scanning calorimetry (DSC) measurements. The hydrophobic acrylic IOLs, ZA9003, and MA60BM, had contact angles ranging from 77.9° ± 0.65° to 84.4° ± 0.09°. The contact angles in the hydrophilic acrylic (970C) and heparin-surface-modified (HSM) hydrophilic acrylic IOLs (BioVue) were 61.8° ± 0.45° and 69.7° ± 0.76°, respectively. The roughness of the IOL optic surface differed depending on the type of IOL (p < 0.001). The surface roughness of BioVue had the lowest value: 5.87 ± 1.26 nm. This suggests that the BioVue IOL may lead to reduced cellular adhesion compared to the unmodified IOLs. All IOLs including those composed of acrylic optic materials from different manufacturers showed distinct Raman spectra peaks. The glass transition temperatures (T_g) for the hydrophobic acrylic IOLs were between 12.5 and 13.8 °C. These results suggest that the intraoperative and postoperative behavior of an IOL can be predicted. This information is also expected to contribute greatly to the industrial production of reliable biocompatible IOLs.

Effect of heparin coating of a foldable intraocular lens on inflammation and capsular bag performance after cataract surgery

PURPOSE

To evaluate the effect of a heparin-coated foldable intraocular lens (IOL) on postoperative flare in high-risk patients.

SETTING

Vienna Institute for Research in Ocular Surgery, Department of Ophthalmology, Hanusch Hospital, Vienna, Austria.

DESIGN

Randomized clinical trial.

METHODS

This study included patients with diabetes mellitus (DM), pseudoexfoliation syndrome (PXF), or both scheduled for cataract surgery in both eyes. One eye received a coated IOL (Polylens EC-1YH PAL) and the other eye, an uncoated control IOL (Polylens EC-1Y PAL). Aqueous flare measurements were taken using a laser flare meter (FM-600, Kowa) preoperatively and 1 hour, 1 day, 3 weeks, and 3 months postoperatively. Visual acuity and anterior (ACO) and posterior (PCO) capsule opacification were assessed, and IOL centration and tilt were measured with a Purkinje meter.

RESULTS

Eighty eyes of 40 patients were included in the study; 64 eyes of 32 patients completed the study. The mean flare values (photons/ms) preoperatively and 1 hour, 1 day, 3 weeks, and 3 months postoperatively were 6.98 ± 3.71 (SD), 19.14 ± 18.90, 16.62 ± 25.33, 10.33 ± 9.70, 8.74 ± 4.64, respectively, with the coated IOL and 8.65 ± 5.73, 22.08 ± 16.23, 13.44 ± 13.71, 7.50 ± 4.11, and 7.03 ± 3.70, respectively, with the control IOL. No significant differences were found in flare, visual acuity, ACO, PCO, tilt, or centration between the coated IOL and the control IOL at any timepoint.

CONCLUSION

No significant differences in flare or capsule performance were found between the coated IOL and control IOL.

Inflammatory cell adhesion and surface defects on heparin-surface-modified poly(methyl methacrylate) intraocular lenses in diabetic patients

PURPOSE

To evaluate the incidence of surface scratches on heparin-surface-modified (HSM) poly(methyl methacrylate) (PMMA) intraocular lenses (IOLs) and the possible influence of these alterations on the biocompatibility of HSM PMMA.

SETTING

University Eye Clinic of Trieste, Trieste, Italy.

METHODS

Twenty-six diabetic patients had phacoemulsification and implantation of an HSM PMMA IOL (809C, Pharmacia & Upjohn). Patients with proliferative diabetic retinopathy or iridopathy were excluded from the study. On postoperative days 7, 30, 90, and 180, specular microscopy was performed to study and photograph the anterior IOL surface. The presence of scratches on the anterior IOL surface was assessed and the inflammatory cell reaction noted and graded using a semiquantitative scale. Finally, the location of the inflammatory cells in relation to the surface scratches was established.

RESULTS

Scratches and other surface defects were found in 88.4% of cases. All patients had small cells on the IOL surface 7 days after surgery. At 30 days, small cells were observed in 88.4% of cases. The inflammatory cells were mainly located inside the scratches rather than throughout the IOL surface.

CONCLUSIONS

This in vivo cytology study provides further evidence of the effectiveness of heparin surface modification in improving the biocompatibility of PMMA. In diabetic patients, inflammatory cells adhered to the exposed PMMA surface more than to the HSM surface, suggesting that the use of HSM PMMA in patients with conditions predisposing them to increased postoperative blood-aqueous barrier breakdown is beneficial.

Posterior capsular opacification with hydrogel, polymethylmethacrylate, and silicone intraocular lenses: two-year results of a randomized prospective trial

PURPOSE

To compare the visual outcome, percentage of posterior capsular opacification, and laser capsulotomy rates with polymethylmethacrylate, silicone, and hydrogel intraocular lens implants at 1 and 2 years postoperatively.

METHODS

Ninety-three eyes of 93 patients were randomized to receive a polymethylmethacrylate, silicone, or hydrogel intraocular lens implant. A standardized surgical protocol was followed by a single surgeon using phacoemulsification with capsulorhexis; any patients with surgical complications were excluded, and all patients received standardized medication and follow-up. Patients were examined at days 1 and 7, months 1, 3, and 6, and years 1 and 2 after surgery. At each assessment, best-corrected logMAR visual acuity and Pelli-Robson contrast sensitivity were measured. Posterior capsular opacification was objectively assessed by digital retroillumination imaging with the use of a dedicated software program and calculated as the percentage area of opacified capsule. Laser capsulotomy was performed if the eye had lost 2 lines of visual acuity with a clinically opaque capsule.

RESULTS

At 2 years postoperatively, the mean percentage area of posterior capsular opacification for hydrogel lenses was 63%; for polymethylmethacrylate, 46%; and for silicone, 17%. Hydrogel intraocular lenses were associated with 17% more posterior capsule opacification than were polymethylmethacrylate lenses (95% confidence interval, 1-33; P =. 037) and 45% more than were silicone lenses (95% confidence interval, 33-58; P <.0001) at 2 years. Polymethylmethacrylate lenses had 28% more posterior capsule opacification than silicone lenses (95% confidence interval, 13-43; P <.0001) at 2 years. Twenty-eight percent of patients with hydrogel intraocular lenses required an Nd:YAG laser posterior capsulotomy at 2 years, compared with 14% with polymethylmethacrylate, whereas no patients with silicone lenses needed a capsulotomy (P =.014). Visual acuity was not significantly different among the three groups, but patients with silicone intraocular lenses had significantly better contrast sensitivity than those with hydrogel lenses (P =.046).

CONCLUSIONS

Intraocular lenses made of this specific hydrogel were associated with a significantly higher degree of posterior capsular opacification and more laser capsulotomies than polymethylmethacrylate and silicone intraocular lenses.

Phacoemulsification and modern cataract surgery

The techniques and results of cataract surgery have changed dramatically during the past three decades. In the USA, we have moved from intracapsular cataract extraction as the preferred technique to almost exclusively extracapsular techniques. Smaller incisions have become the standard, with phacoemulsification now being the method of choice for most surgeons. Along with these advances have come improved intraocular lens materials and designs, especially well suited for use with smaller incisions. Phacoemulsification as a method to remove the cataractous lens was first proposed more than 20 years ago. Advances in techniques and equipment have led to a dramatic increase in the popularity of phacoemulsification with increased safety and efficiency. Viscoelastic agents have been developed synchronously with modern phacoemulsification techniques, playing an integral role in the success of this new technology. Improved surgical techniques for removing the anterior lens capsule have decreased the incidence of both intraoperative and postoperative capsular complications. Nucleus removal, formerly performed primarily in the anterior chamber, is now performed in the posterior chamber, decreasing damage to the corneal endothelium. Improved wound construction allows many wounds to be left unsutured, and smaller wounds allow shorter recovery time and greater intraoperative control and safety. Intraocular lenses can have smaller optic sizes and still maintain accurate centration. Foldable intraocular lenses can take advantage of the smaller incision, even further shortening the time to visual recovery. Continual evolution of this technology promises to further improve patient outcomes after cataract surgery.

Adhesion mechanisms of human lens epithelial cells on 4 intraocular lens materials

PURPOSE

To evaluate lens epithelial cell (LEC) adhesion on different intraocular lens (IOL) materials with particular attention to the distribution of proteins located in the focal contacts.

SETTING

Center of Biotechnological and Clinical Research in Ophthalmology, University of Bologna, Italy.

METHODS

The IOL materials tested were poly(methyl methacrylate) (PMMA), heparin-surface-modified PMMA (HSM PMMA), polyHEMA, and silicone. Primary cultures of human LECs were established from human anterior capsules obtained during cataract surgery. The mean number of cells attached per square millimeter was calculated for each material after 24 and 72 hours. Transmission electron microscopy and immunocytochemical analysis were performed to detect the proteins actin, vinculin, and talin.

RESULTS

Mean adhesiveness of human LECs increased over time with PMMA and decreased with the other materials. At 72 hours, mean LECs ranged from 54.8 cells/mm2 +/- 12.8 (SD) on PMMA to 2.1 +/- 0.7 cells/mm2 on silicone. The means for HSM PMMA and polyHEMA fell in between. The cytoskeletal proteins were arranged to produce focal contacts in only the LECs cultured on PMMA. The LECs cultured on polyHEMA, HSM PMMA, and silicone attached but failed to develop focal contacts or stress fibers.

CONCLUSION

This study confirms the multifactorial pathogenesis of posterior capsule opacification and suggests its incidence will be reduced by improving surgical techniques and using IOL surfaces that discourage cell adhesion.

Intraocular lens materials and styles: a review

Biomaterial science has lead to the development of a variety of foldable intraocular lens (IOL) biomaterials. This literature review examines these lenses from both a basic science and a clinical perspective. By most parameters, hydrogel, soft acrylic and silicone IOL are better than polymethylmethacrylate (PMMA) lenses. Plate haptic silicone IOL have the lowest incidence of cystoid macula oedema and posterior capsule opacification, but these lenses require an intact anterior capsularhexis and posterior capsule. Yttrium aluminium garnet (YAG) laser capsulotomy must be delayed at least 3 months to avoid posterior lens dislocation. Silicone has the lowest threshold for YAG laser damage of all IOL materials and also adheres irreversibly to silicone oil with subsequent optical impairment. Three piece silicone IOL with polypropylene haptics have a higher incidence of decentration, pigment adherence and capsule opacification compared with PMMA haptics. Hydrogel lenses are very biocompatible and resistant to YAG laser damage, but pigment adheres to the surface more readily than PMMA. Soft acrylic IOL unfold slowly, resulting in controlled insertion, but it is possible to crack the lens and some lenses develop glistenings due to water accumulation. There are significant socioeconomic implications to the large differences in posterior capsule opacification rates between the various biomaterials and the lens styles.

Postoperative cellular reaction on various intraocular lens materials

PURPOSE

The presence of cellular deposits on the surface of intraocular lenses (IOLs) is a manifestation of: (1) the breakdown of the blood-aqueous barrier produced by surgery; and (2) foreign body reaction induced by lens implantation. The purpose of this study was to assess the presence of cellular deposits on the surfaces of various IOL materials.

METHODS

Fifty patients scheduled for cataract surgery were randomized into five groups of ten patients each and received IOLs of the following materials: conventional polymethylmethacrylate (PMMA), surface-passivated PMMA, heparin-surface modified PMMA, poly-hydroxyethylmethacrylate (HEMA) hydrogel and silicone. Patients were examined at 7 days, 30 days, 90 days, and 180 days after surgery. All eyes were observed first via slit-lamp and then using a contact specular microscope for photographic documentation.

RESULTS

Small, spindle-shaped cells were observed on all IOLs in the early postoperative period. Epithelioid cells appeared approximately 30 days after surgery on all PMMA IOLs, but most particularly on conventional PMMA IOLs. No cells were observed on poly-HEMA and silicone IOLs.

CONCLUSIONS

The decreased number of epithelioid cells discovered in the early postoperative period may indicate a reduction in the inflammatory process induced by surgery. The permanence of epithelioid cells on IOL surfaces may be a sign of foreign body reaction. The results of this study indicated that poly-HEMA and silicone IOLs showed fewer cellular deposits than PMMA IOLs, suggesting that they may be better tolerated than PMMA IOLs.

Heparin-surface-modified intraocular lens implantation in eyes with pseudoexfoliation syndrome

Eyes with pseudoexfoliation syndrome have a greater risk of intraoperative and postoperative complications. Clinical and histopathological studies indicate that heparin-surface-modified intraocular lenses (HSM IOLs) can reduce postoperative anterior segment inflammation. Our study evaluated the blood-aqueous barrier permeability in eyes with pseudoexfoliation syndrome and implanted with an HSM IOL. We examined two groups of 20 patients, one comprising patients with pseudoexfoliation syndrome and one a sex- and age-matched control group with senile cataracts. Each group was divided into two subgroups of ten patients each. In one subgroup, an HSM IOL was implanted; in the other, a conventional poly(methyl methacrylate) IOL. We performed a complete ophthalmologic examination and iris angiography preoperatively and at 30, 90, and 180 days after surgery. Fluorophotometry was performed at the 90-day and 180-day postoperative examinations. The patients with pseudoexfoliation syndrome had a higher blood-aqueous barrier permeability than did the control group. Permeability decreased significantly three and six months after surgery, especially in the HSM IOL group.

Reduced bacterial adhesion to heparin-surface-modified intraocular lenses

Bacterial adherence to intraocular lenses (IOLs) could be the cause of endophthalmitis following cataract surgery and lens implantation. There are previous reports that heparin bound to the surface of poly(methyl methacrylate) (PMMA) IOLs reduces cell adhesion. In this study, the in vitro adherence of Staphylococcus epidermidis, Staphylococcus aureus, and Pseudomonas aeruginosa to regular PMMA IOLs and to heparin-surface-modified (HSM) PMMA IOLs was investigated. The three bacterial strains attached in significantly lower numbers to HSM-PMMA IOLs than to PMMA IOLs (P < .01). Heparin in solution also inhibited attachment of Staphylococcus epidermidis to regular PMMA IOLs. Heparin may reduce adherence by placing a highly hydrated layer between the bacteria and the IOL surface. Therefore, the use of HSM-PMMA IOLs could diminish the incidence of endophthalmitis.

The Binkhorst Medal Lecture. Biologic relationship between poly(methyl methacrylate) intraocular lenses and uveal tissue

Implantation of a poly(methyl methacrylate) (PMMA) intraocular lens (IOL) after cataract surgery is associated with breakdown of the blood-ocular barrier and a foreign body inflammatory response. Although the material is biocompatible, it is not inert. The history of PMMA IOL implantation has reflected mechanical, chemical, and immunological interactions between the IOL and ocular tissues. The common link in these events is instability of the blood-ocular barrier. In this lecture, I discuss the nature of these interactions and present evidence that currently investigated methods of surface modification and capsular bag IOL implantation are effective in stabilizing the blood-ocular barrier.