Evaluation of Two Rabbit Ocular Implantation Models Using Polymethylmethacrylate Intraocular Lenses

Abstract

Polymethylmethacrylate (PMMA) is the standard intraocular lens (IOL) optic material based upon its long history of clinical use, stability and biocompatibility. Regulatory guidelines require IOLs that utilize novel lens material to be evaluated for biocompatibility in a long term (1 year) ocular implant study using an appropriate species and a reference IOL, e.g., PMMA. The purpose of this study was to evaluate the rabbit as a potential model for conducting long-term ocular implant studies that satisfy regulatory biocompatibility guidelines. In this study, lensectomy by phacoemulsification with implantation of PMMA IOLs in the capsular bag was performed on one group of rabbits, while a second group received only implantation of PMMA wafers (3 x 5 x 0.4mm) in the anterior chamber without lensectomy. Animals received ocular examinations at selected intervals during the study, e.g., slit-lamp biomicroscopy. Except for the expected postoperative inflammation, no signs of inflammation were observed in either rabbit model for up to approximately 3 months following implantation of the PMMA IOLs. However, after about 3 postoperative months rabbits with the PMMA IOLs in the capsular bag developed posterior synechiae, posterior capsular opacification (pearls and fibrosis), uveitis, and secondary cataracts. In some rabbits extrusion/displacement of the IOL haptics caused mechanical trauma to the iris with subsequent hyphema. In contrast, the rabbits that were implanted with the PMMA wafers in the anterior chamber did not display any signs of inflammation during a one year study period. Histopathology confirmed the presence of the ocular inflammation which was observed in the rabbits with the IOLs implanted in the capsular bag. These results demonstrate that studies using the rabbit to evaluate IOLs following lensectomy and capsular bag implantation should be limited to a shorter study duration of 6 months or less. In contrast, a longer study duration of up to one-year may be conducted in rabbits following implantation of IOL wafers into the anterior chamber. Fur-thermore, these studies demonstrate that the site of implantation and duration of study can influence results obtained in an ocular biocompatibility study.