Biologic Keratoprosthesis Materials

Abstract

The keratoprosthesis (KPro; “artificial cornea”) offers patients with cornea blindness, the hope of visual recovery. The first KPro designs entailed placing an optically clear material through an opaque cornea. Although introduced over 200 years ago, the basic concept is retained in many of the modern KPro designs. The Boston KPro, employs a polymethylmethacrylate (PMMA) (inert plastic) optic stabilized between a front and back plate. With over 2000 implanted world-wide to date, the Boston KPro has an excellent retention rate in patients who have failed prior penetrating keratoplasties, but lack chemical injuries or auto-immune cicatricial diseases, such as Stevens-Johnson syndrome or pemphigoid. From the Boston KPro multicenter study, the patient population who had a primary diagnosis of graft rejection retained the KPro in 97% of the eyes with a mean follow-up of 8.5 months.1 However, patients with cicatricial autoimmune disease had a retention rate of 83% and those with chemical injuries as a primary diagnosis had an 89% retention rate. Over a longer follow-up period, the retention rate decreases further for patients with autoimmune diseases and chemical injuries.2,3 For this subset of desperate patients, we continue to search for methods of increasing the retention rate of a KPro. Some KPro models differ from early designs by surrounding a central optic with a carrier or haptic that is intended to “biointegrate” with the cornea. In theory, the KPro could potentially integrate with the cornea epithelium, stroma, endothelium, or a combination of the corneal layers. Most of the “biointegratable” KPro research has focused on integration with either the cornea epithelium or the stomal keratocytes. Integration with the cornea epithelium may offer the advantage of a barrier to infection, but it would offer little structural support. Given that the stroma comprises about 90% of the cornea thickness, a type of stromal adhesion may increase the structural integrity of a KPro. Bio-integratable KPro designs can be separated into autologous biologic models and other models derived from biologic materials. These models include biologic haptics, coatings, and scaffolds. This paper will review both the clinical use of and the research on biologic KPro models.