Patricia M. Knight

Surface properties of intraocular lens materials and their influence on in vitro cell adhesion.

ABSTRACT An in vitro model to assess lens epithelial cell adhesion to a variety of intraocular lens materials was developed. Rabbit anterior lens capsules Were isolated and cultured in serum‐containing medium. Test surfaces included poly(methyl methacrylate), two new silicones (SLM‐1/UV, SLM‐2/UV) two hydrogels (HEMA, Lidofilcon A), and polytetrafluoroethylene(PTFE). Following the application and culturing of cells on the test surfaces, adherent cells were removed by trypsinization and counted at eight and 24 hours. The material surfaces were characterized by electron spectroscopy for chemical analysis and scanning electron microscopy. The captive bubble technique was also used to assess interfacial free energy. More cells adhered to PMMA than to the other materials tested (P < .01). The two silicones, HEMA, and PTFE did not differ significantly from each other; Lidofilcon A had the lowest cell adhesion of all materials tested. Cell adhesion results were related to the interfacial free energy of each material. Materials of low (< 5 ergs/cm2) or high (>40 ergs/cm2) interfacial free energies had lower cell adhesion than materials of intermediate free energies (5 to 40 ergs/cm2) which exhibited the highest cell adhesion.

Assessment of the long-term corneal response to hydrogel intrastromal lenses implanted in monkey eyes for up to five years.

ABSTRACT The biocompatibility of hydrogel intracorneal lenses (ICLs) implanted in monkey eyes was evaluated for periods ranging up to five years. Seventy‐three plus or minus powered ICLs made of Lidofilcon A (68% water) or Lidofilcon B (79% water) were implanted following lamellar dissection with a microkeratome. Ten sham surgical procedures were performed without ICL implantation as controls. Eyes were followed for up to five years by slitlamp biomicroscopy and specular microscopy. Light and transmission electron microscopic evaluations of enucleated eyes were performed at various intervals. Minimal tissue reaction was noted; both hydrogel materials appeared to be equally well tolerated. Failures usually occurred as a result of microkeratome problems encountered during surgery. Histopathological changes to the cornea included epithelial thinning anterior to the thickest portion of the ICL, fibroblastic activity along the ICL‐stromal interface, and deposition of an amorphous extracellular material adjacent to the ICL. These observations did not appear to be clinically significant as the eyes were quiet by slitlamp examination. Removal of three ICLs eight to ten months prior to enucleation restored the normal histological characteristics of the cornea. The endothelial cell density of ICL‐implanted eyes decreased by 4.3% (n =17) six months after surgery but remained stable thereafter. The variation in endothelial cell area and percentage of hexagonal cells did not change over 50 months. The results appear to demonstrate that high water content synthetic ICLs can be well tolerated in the monkey cornea for up to five years.

Contact-angle analysis of intraocular lenses.

Purpose: To present contact‐angle measurements of commercially available intraocular lenses (IOLs) in air and in water to facilitate the understanding of how various OLs might interact in different environments. Setting: Laboratory. Methods: Five commercially available IOLs were studied: AMO® DuraLens® PS‐59NB™, AMO PhacoFlex® SI‐26NB™, AMO PhacoFlex II® SI‐30NB®, Chiron® ChiroFlex® C10UB, and Alcon® AcrySof® MA60BM. The AMO soft acrylic model AR40™, currently under clinical study, was also evaluated. Contact‐angle measurements were made in air and in water using sessile drop and captive bubble methods. Results: The sessile drop method indicated that all materials were hydrophobic in air. The captive bubble method differentiated materials based on their polar and dispersive forces. Conclusion: Contact‐angle measurements differed depending on the test conditions. Proper choice of contact‐angle measurement method can generate useful information about a material surface and its potential biomaterial interactions.

Evaluation of the biocompatibility and fixation of a new silicone intraocular lens in the feline model

ABSTRACT The biocompatibility and fixation of a new silicone intraocular lens was evaluated in the cat eye. Following extracapsular lens extraction, 14 cats were implanted with a silicone lens (SLM 2/UV type) with polypropylene modified J loops in one eye and a poly(methyl methacrylate) (PMMA) lens (Perspex CQ of a similar design in the fellow eye. Half the lenses were placed in the ciliary sulcus and half in the capsular bag. The eyes were evaluated for up to one year. Neither lens material showed any signs of toxicity clinically or histopathologically. Both lenses achieved stable fixation in the capsular bag; however, some inflammatory reaction and lens dislocation were noted with sulcus placement of both lens types. The amount of proteinaceous and cellular debris on the explanted silicone lenses was significantly less than that on the PMMA lenses as assessed with methylene blue staining. All retrieved lenses were optically clear and no significant change in the lens surface morphology, clarity and/or optical properties was observed.

Evaluation of the chemical, optical, and mechanical properties of elastomeric intraocular lens materials and their clinical significance

ABSTRACT The current trend toward small incision cataract surgery has resulted in the use of elastomers as intraocular lens materials. Little has been published on appropriate methods of evaluating biomaterials intended for implantation in the eye. We present a methodology for such a study and report the results for two elastomeric silicone intraocular lens materials. The chemical, optical, and mechanical properties of the two materials were evaluated, as was their stability to hydrolytic and ultraviolet degradation. Qualitative correlations between these properties and clinical requirements are discussed. Both silicone materials possessed the necessary properties for use as small incision intraocular lenses.

Assessing intraocular lens calcification in an animal model

Purpose: To describe an animal model used to evaluate the propensity of various biomaterials to calcify intraocularly. Setting: Research Department, Allergan Inc., Irvine, California, USA. Methods: Intraocular lens (IOL) optic materials were implanted intramuscularly and/or subcutaneously in rabbits for up to 90 days. The materials included silicone, poly(methyl methacrylate) (PMMA), hydroxyethyl methacrylate hydrogel, and several hydrophobic acrylic materials. Scanning electron microscopy (SEM) and energy dispersive x‐ray spectroscopy (EDS) were used to detect calcification demonstrated by characteristic discrete nodules containing both calcium and phosphate. Histological methods were used to evaluate tissue reactivity. Disc lenses fabricated from the experimental material were also bilaterally implanted in rabbit eyes that were monitored by slitlamp biomicroscopy. The lenses were explanted at 1, 2, 5.5, 10, and 20 months for SEM/EDS analysis. Results: No calcification was noted in the intramuscularly or subcutaneously implanted silicone, PMMA, and acrylic optic materials. Calcification was noted on the intramuscularly, subcutaneously, and intraocularly implanted experimental acrylic and the intramuscularly implanted hydrogel material; the calcification was more extensive on the hydrogel. Signs that suggested intraocular calcification were first noted on the experimental IOLs at 4 months, but calcification was not confirmed until 10 months. Conclusions: Material calcification occurred more quickly in an intramuscular or subcutaneous environment than in an intraocular environment. Intramuscular and subcutaneous implantation appears to be an excellent model for screening materials for calcification potential. However, calcification is both host environment and material dependent. Using intramuscular or subcutaneous implantation in animal models to predict intraocular calcification in humans must be done with caution.

Hydrolysis of a Neutral Hydrogel and Biomolecule Attachment to Increase Cell Adhesion and Migration

Tissue epikeratophakia is a surgical procedure where a processed human corneal tissue is implanted onto the surface of a recipient cornea for refractive correction. The procedure was originally described by Barraquerl and clinical trials were conducted in the United States under the tradename KeratoLensTM. The surgical procedure involves removal of the surface epithelium, creating a peripheral mid-depth pocket in the recipient cornea, and tucking in and suturing the periphery of the rehydrated tissue lens. After implantation the tissue graft must reepithelialize and clear before the final visual outcome can be determined.