Long-Term Biocompatibility of PEG/PAA Hydrogel by Intrastromal Implantation in Rabbit Cornea

Abstract

Purpose: : To assess the long-term biocompatibility of the polyethylene glycol and polyacrylic acid (PEG/PAA) interpenetrating network hydrogel designed for artificial cornea and intrastromal lens.

Methods: : A microkeratome was used to create a stromal flap (12-mm diameter, 3-mm hinge) at a depth of 250 µm. The hydrogel (6-mm diameter, 30-40 µm thick) was implanted in the stroma of ten rabbits for 2, 6, 9, 12, and 16 months. After implantation, eyes were treated with 1% prednisolone and topical antibiotics for five days. Eyes were examined bi-weekly or monthly and evaluated with conventional histology and immunohistochemistry after enucleation.

Results: : At two months, all corneas remained clear without infection; however, complications arose in four of six rabbits receiving the implant for six months or longer. Polymer extrusion occurred in one case. The other three developed focal epithelial defects over the implant edge. One of these also developed diffuse corneal opacity with neovascularization. In eyes with identified complications, macrophages were found at the polymer edge and the posterior stroma underneath the implant. Histological evaluation showed no epithelial ingrowth at the flap edge.

Conclusions: : Intrastromal implantation of PEG/PAA led to long-term complications in the rabbit cornea. Our collaborators at Singapore Eye Research Institute, however, implanted the same hydrogel samples in rabbits with smaller, 3-mm wide stromal pockets and applied steroids for one month following surgery. Corneas were clear for up to one year. Therefore, the biocompatibility may be dependent on the size of the incision and/or duration of steroid treatment.

Keywords: keratoprostheses • refractive surgery: other technologies