Keratoprostheseis (KPRO)
Keratoprosthesis implantation is a procedure that involves full-thickness removal of the cornea and replacement by an artificial cornea. The Boston Type I Keratoprosthesis is currently the most commonly used keratoprosthesis device in the US. It consists of a clear plastic polymethylmethacrylate (PMMA) optic and back plate sandwiched around a corneal graft and secured with a titanium locking ring (Figure 15). After the device is assembled, a partial-thickness trephination is performed on the host cornea. Full-thickness resection of the patient’s cornea is then completed using curved corneal scissors. The keratoprosthesis is then secured to host tissue using interrupted or running sutures. Generally, patients who have a history of multiple failed PKs are candidates for a keratoprosthesis transplant. Other indications include severe keratitis or ocular surface disease resulting from limbal stem cell failure, such as Stevens-Johnson syndrome (Figure 16), ocular cicatricial pemphigoid, aniridia (Figure 17) and chemical injury (1, 13). The Boston Type II Keratoprosthesis is a similar device with a longer optic designed to extend through an opening made in the upper eyelid (Figure 19). It is indicated for the most severe cicatrizing ocular surface diseases.