Assessing intraocular lens calcification in an animal model

To describe an animal model used to evaluate the propensity of various biomaterials to calcify intraocularly.

Research Department, Allergan Inc., Irvine, California, USA.

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.

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.

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.