Long–term Corneal Biocompatibility To Pfpe Polymers – Histological Findings

Abstract

Abstract: : Purpose: Perfluoropolyether (PFPE) polymers are candidates for corneal inlays for refractive correction as they offer suitable chemical stability, transparency, porosity and surface characteristics. This study focused on long–term morphological corneal changes after implantation of a PFPE inlay.Methods: PFPE was cast into lenticules 4.25mm in diameter and 100 microns thick centrally, with a 8.8mm radius of curvature. A LASIK–style corneal flap 80–120 microns deep was cut in the cornea of one eye of 15 rabbits using a microkeratome. An PFPE lenticule was placed under the corneal flap in 10 animals, with 5 being maintained as sham wounds. Animals were maintained for either 6, 12 and 24 months. The corneal tissue response to the surgery and implanted lenticule were regularly assessed by biomicroscopy. Optical clarity of the inlays was evaluated using back scattering with biomicroscopy. Animals were terminated at predetermined timepoints and tissue examined under light and electron microscopy. Results: Clinically, the operated eyes in all animals were quiet with corneal tissue anterior and posterior to the corneal flap remaining clear. Two animals with implanted corneas were discontinued; one on day 244 due to a small split in the inlay, one on day 523 due to protrusion of the inlay edge. Excluding these, the study included 3 animals at each of the 6 and 12 month timepoints (n=2 implanted, n=1 sham) and 7 animals at 24 months (n=4 implanted, n=3 shams). All inlays maintained a high level of optical clarity as evaluated by backscattering. Histologically, epithelium of the sham–wounded corneas over the corneal flap was 5 layers thick with cuboidal basal cells. In each case, an intact lenticule was present beneath a LASIK flap composed of stromal tissue with an adherent stratified epithelium (5 layers thick with cuboidal basal cells). Stromal tissue anterior and posterior to the lenticule appeared normal with slight accumulation of keratocytes in places along the lenticule surface although this did not increase with time and there was no evidence of fibrous capsule formation. Conclusions: The PFPE lenticules showed excellent long–term biocompatibility and optical clarity following implantation as a corneal inlay in the rabbit cornea.

Keywords: cornea: clinical science • clinical (human) or epidemiologic studies: outcomes/complications