Sandwich theory: bioactivity-based explanation for posterior capsule opacification.

PURPOSE: To present a bioactivity-based explanation for posterior capsule opacification (PCO) formation after cataract surgery. SETTING: Central Hospital, Vaasa, Finland. METHODS: The sandwich theory was based on findings in a keratoprosthesis study in which bioactivity of the prosthesis seemed to prevent epithelial downgrowth and clinical findings of the behavior of the AcrySof intraocular lens (IOL). The theory was formulated to explain PCO formation after cataract surgery with posterior chamber IOL implantation. RESULTS: If the IOL were of a bioactive material, it would allow a single lens epithelial cell to bond both to the IOL and the posterior capsule. This would produce a sandwich pattern including the IOL, the cell monolayer, and the posterior capsule. The sealed sandwich structure might prevent further epithelial ingrowth and PCO. CONCLUSION: The degree of IOL bioactivity could explain the difference in PCO and the neodymium:YAG rates with different IOL materials. In theory, a bioactive IOL would prevent PCO better than poly(methyl methacrylate) and silicone IOLs, which have good biocompatibility but are bioinert.

Evaluation of a 3-piece silicone intraocular lens with poly(methyl methacrylate) haptics.

PURPOSE: To evaluate the safety and performance of a foldable silicone intraocular lens (IOL) in small incision phacoemulsification surgery. SETTING: Vaasa Central Hospital, Vaasa, Finland. METHODS: Phacoemulsification with primary implantation of a posterior chamber IOL was performed in 50 patients. All eyes were implanted with a CeeOn IOL (model 920, Pharmacia & Upjohn) with a silicone optic and poly(methyl methacrylate) haptics. The ease of folding, implanting, and unfolding the IOL in the bag were recorded. Visual acuity, postoperative complications, optic decentration, and optic tilt were measured at 5 postoperative visits. The IOLs were evaluated for haze and discoloration and the IOL surface, for inflammatory or pigment deposits. Follow-up was 12 months. RESULTS: In 44 of 50 cases, folding the IOL was easy, and in 46 of 50, unfolding the IOL was controlled. The mean follow-up was 11.45 months +/- 0.52 (SD). No postoperative complications occurred, and 96% of patients achieved a best corrected visual acuity (BCVA) of 0.5 or better and 56%, a BCVA of 1.0 or better. The IOL decentration was less than 0.25 mm in 89% of cases, and there was no optic tilt. The neodymium:YAG laser capsulotomy rate was 11%. CONCLUSION: Good visual outcome and excellent centration were achieved with the CeeOn model 920 IOL. It is therefore suitable for small incision cataract surgery. Because of the IOL's smooth, polished surface, the choice of instruments for folding and implantation is important.

Intraocular lens bioactivity tested using rabbit corneal tissue cultures.

PURPOSE: To evaluate the effects of different intraocular lens (IOL) materials on epithelial cell growth to test the sandwich theory; i.e., a bioactivity-based explanation of posterior capsule opacification (PCO) after cataract surgery. SETTING: Central Hospital, Vaasa, and Institute of Dentistry and Turku Center for Biomaterials, University of Turku, Finland. METHODS: Rabbit corneal tissue cultures were set up on poly(methyl methacrylate) (PMMA), heparin-surface-modified (HSM) PMMA, silicone, acrylate, and hydrogel IOLs for 1 week. The tissue consisted of intact epithelium and half the thickness of the corneal stroma, which was placed against the IOL. The growth of the epithelium was examined by light microscopy to evaluate the attachment of the corneal explant to the IOL surface. RESULTS: All tissue samples grew well under the culture conditions. When grown on PMMA, HSM PMMA, silicone, and hydrogel, the tissue did not attach to the IOL or the epithelium grew around the explant, suggesting that the attachment of the stroma to the IOL was poor or nonexistent. Some explants on acrylate IOLs attached directly to the IOL surface with no epithelial ingrowth between the stroma and the IOL. CONCLUSIONS: This tissue culture method can be used to examine the behavior of corneal tissue in contact with different IOL materials. The results suggest that the acrylate IOL may have bioactive properties. This, with the lens optic's square edge, may hinder lens epithelial cell proliferation and thus prevent PCO.

Adhesion of soluble fibronectin, laminin, and collagen type IV to intraocular lens materials.

PURPOSE: To evaluate soluble fibronectin, laminin, and collagen IV adhesion to poly(methyl methacrylate) (PMMA), heparin-surface-modified (HSM) PMMA, silicone, acrylate, and hydrogel intraocular lenses (IOLs). SETTING: Department of Medical Biochemistry, University of Oulu, Oulu, Finland. METHODS: Seventy-five IOLs were incubated for 24 hours at 37 degrees C with radioactive iodine labeled soluble fibronectin, laminin, or collagen type IV. Twenty-five IOLs were analyzed for each protein, 5 of each type. The amount of absorbed protein was measured with a gamma counter and expressed as counts per minute (cpm). RESULTS: Fibronectin bound best to the acrylate IOL; the differences between the acrylate and the other materials, except PMMA, were significant (P < .01 to .001; PMMA P = .31). Although significantly more laminin bound to acrylate than to PMMA, HSM PMMA, or silicone (P < .05 to .001), hydrogel had the highest overall binding of this protein (P < .001 to .0001). Hydrogel also had significantly higher binding of type IV collagen than the other IOLs (P < .01 to .0001). CONCLUSIONS: It can be hypothesized that if an IOL has more fibronectin bound to it, the IOL can also attach to the capsule better as it consists mainly of collagen. The stronger binding of fibronectin and laminin to acrylate IOLs could be an explanation for the better adhesion of the acrylate IOL to the anterior and posterior capsules and thus for the lower rate of posterior capsule opacification.

Adhesion of fibronectin, vitronectin, laminin, and collagen type IV to intraocular lens materials in pseudophakic human autopsy eyes. Part 1: histological sections.

PURPOSE: To evaluate fibronectin, vitronectin, laminin, and collagen type IV adhesion to poly(methyl methacrylate) (PMMA), silicone, hydrophobic soft acrylate, and hydrogel intraocular lenses (IOLs) in pseudophakic human autopsy eyes. SETTING: Center for Research on Ocular Therapeutics and Biodevices, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA. METHODS: Thirty-eight autopsy eyes containing PMMA, silicone, hydrophobic acrylate, or hydrogel IOLs were assessed. Histological sections were prepared from each eye, and immunohistochemical analyses were performed for fibronectin, vitronectin, laminin, and collagen type IV. One hundred fifty-two specimens were analyzed. RESULTS: A sandwich-like structure (anterior or posterior capsule/fibronectin/1 cell layer/fibronectin/IOL surface) was seen in 12 of 14 autopsy eyes with soft acrylate IOLs, 3 of 10 with a PMMA IOL (P =.0094), 1 of 10 with a silicone IOL (P =.0022), and 0 of 4 with a hydrogel IOL (P =. 0041). The thicker fibrocellular tissue on the inner surface of the anterior or posterior capsule that was in contact with silicone IOLs was lined with collagen type IV. Vitronectin and laminin were not found at the fibrocellular tissue-IOL interface in any specimen. CONCLUSIONS: This study seems to confirm the sandwich theory of posterior capsule opacification in eyes with an IOL and suggests that fibronectin may be the major extracellular protein responsible for the attachment of hydrophobic soft acrylate (AcrySof(R)) IOLs to the capsular bag. This may represent a true bioactive bond between the IOL and lens epithelial cells or between the IOL and the capsular bag and may be one reason the PCO and neodymium:YAG capsulotomy rates are lower in eyes with a soft acrylate IOL.

Adhesion of fibronectin, vitronectin, laminin, and collagen type IV to intraocular lens materials in pseudophakic human autopsy eyes. Part 2: explanted intraocular lenses.

PURPOSE: To evaluate fibronectin, vitronectin, laminin, and collagen type IV adhesion to poly(methyl methacrylate) (PMMA), silicone, hydrophobic soft acrylate, and hydrogel intraocular lenses (IOLs) in human pseudophakic autopsy eyes. SETTING: Center for Research on Ocular Therapeutics and Biodevices, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA. METHODS: Thirty-two autopsy eyes containing PMMA, silicone, soft acrylate, or hydrogel IOLs were assessed. The IOLs were explanted from the capsular bag, and both sides of the IOLs were immunohistochemically stained for fibronectin, vitronectin, laminin, or collagen type IV. The number of cells on the IOL surfaces was counted. The capsular bag from 1 eye containing a soft acrylate IOL was examined for fibronectin and vitronectin. RESULTS: Hydrophobic soft acrylate IOLs had significantly more fibronectin adhering to their surfaces than PMMA (P <.01) or silicone (P <.01) IOLs, as well as more vitronectin. Silicone IOLs had more collagen type IV adhesion than the other IOLs (P <.05-.06). Collective protein adhesion differed significantly between soft acrylate IOLs and PMMA and silicone IOLs, but not between PMMA and silicone IOLs. CONCLUSIONS: The greater amount of protein on the hydrophobic soft acrylate (AcrySof(R)) IOLs seems to support an adhesive mechanism for their attachment to the capsular bag. Fibronectin and vitronectin have functional domains to bind them to lens epithelial cells and the collagenous capsule. This kind of attachment could be a true bioactive bond and may be 1 reason the PCO and neodymium:YAG capsulotomy rates are lower in eyes with a soft acrylate IOL.

Titanium and bioactive glass-ceramic coated titanium as materials for keratoprosthesis.

The current problem with keratoprosthesis is the ingrowth of corneal or conjunctival epithelium into the anterior chamber. This may lead to infections and extrusion of the prosthesis as well as to the development of retroprosthetic membrane and secondary glaucoma. Glass-ceramic coated and uncoated titanium has been tested as material for the keratoprosthesis to prevent epithelial ingrowth. Twenty-two Supra-Descemet's membrane keratoprostheses were inserted in the eyes of 22 rabbits for 1, 2, 4, 8, or 12 months. The prosthesis had an optic part made of polymethylmetacrylate (PMMA). The support for the optic part and the flange of the prosthesis were made of titanium. Eleven of the prostheses were coated with glass-ceramic. The histological sections of the enucleated eyes were prepared through the central part of the cornea and the prosthesis using a cutting-grinding method. The histological analysis was made on both halves of the implants separately giving two analysis areas in each eye. All 11 titanium prostheses were retained for the time period planned. Two glass-ceramic coated prostheses were lost at 2 and 4 weeks, respectively. This was caused by difficulties at surgery due to a thick coating. These eyes were excluded from the histological analysis. No significant ingrowth of epithelium was seen in 15/18 (83%) and in 16/22 (73%) of the analysed areas of the glass-ceramic coated and titanium prostheses, respectively. Titanium appears to be a suitable material for the keratoprosthesis. The ingrowth of the epithelium may be hindered further by coating the titanium with bioactive glass-ceramic.