Assessing intraocular lens calcification in an animal model

Purpose: To describe an animal model used to evaluate the propensity of var ious biomaterials to calcify intraocularly. Setting. Research Department, Allergan Inc., Irvine, California, USA. Methods. Intraocular lens (IOL) optic materials were implanted intramuscula rly and/or subcutaneously in rabbits for up to 90 days. The materials inclu ded silicone, poly(methyl methacrylate) (PMMA), hydroxyethyl methacrylate h ydrogel, and several hydrophobic acrylic materials. Scanning electron micro scopy (SEM) and energy dispersive x-ray spectroscopy (EDS) were used to det ect calcification demonstrated by characteristic discrete nodules containin g both calcium and phosphate. Histological methods were used to evaluate ti ssue 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 fo r SEM/EDS analysis. Results: No calcification was noted in the intramuscularly or subcutaneousl y implanted silicone, PMMA, and acrylic optic materials. Calcification was noted on the intramuscularly, subcutaneously, and intraocularly implanted e xperimental acrylic and the intramuscularly implanted hydrogel material; th e calcification was more extensive on the hydrogel, Signs that suggested in traocular calcification were first noted on the experimental IOLs at 4 mont hs, but calcification was not confirmed until 10 months. Conclusions: Material calcification occurred more quickly in an intramuscul ar or subcutaneous environment than in an intraocular environment. Intramus cular and subcutaneous implantation appears to be an excellent model for sc reening materials for calcification potential. However, calcification is bo th host environment and material dependent. Using intramuscular or subcutan eous implantation in animal models to predict intraocular calcification in humans must be done with caution.