Prosthesis in a pocket

The KeraKlear (KeraMed) artificial cornea, a new foldable keratoprosthesis designed for implantation into an intrastromal pocket, is a safe and effective option in eyes with blinding ocular surface disease that are unsuitable for penetrating keratoplasty, according to A John Kanellopoulos MD, Clinical Professor of Ophthalmology, New York University School of Medicine, USA. “This is an implantable keratoprosthesis that does not penetrate the cornea, so it reduces the risk of intraocular infection and haemorrhage. It also leaves open the options of performing a penetrating keratoplasty or implantation of a Boston keratoprosthesis at a later time,” he told the 20th ESCRS Winter Meeting in Athens, Greece. The hydrophilic acrylic material of the KeraKlear keratoprostheses received its CE mark in 2009, although the implant is not as yet FDA approved. The device has a diameter of 7.0mm with a 3.5mm central optic. It also has fenestrations on its periphery to allow the passage of fluid and nutrients. Implantation of the keratoprosthesis involves first creating an intrastromal pocket with a femtosecond laser followed by a partial thickness central 3.5mm diameter trephination. The implant is then inserted through the trephination and its edges are manipulated into the laser created pocket with a forceps, Dr Kanellopoulos explained. The pocket creation and trephination removes only around five per cent of the corneal volume and requires four sutures at most for secure placement. By comparison, the Boston keratoprosthesis requires 8.0mm diameter full thickness trephination and 16 to 24 sutures to secure the implant’s donor cornea vehicle. In a study involving 11 patients with severe ocular surface disease who underwent implantation of the KeraKlear keratoprosthesis, visual acuity improved from light perception to 20/100-20/80 within the first postoperative week. In addition, the central cornea remained clear and vision remained stable throughout four years of follow-up. The conditions affecting the patients included alkali burn, ocular cicatricial pemphigoid, and aniridia. In all patients the recovery of visual acuity was limited by coexisting macular disease and/or advanced glaucoma. There was one case of corneal melt, but no cases of extrusion. Dr Kanellopoulos noted that corneal melt has also been one of the main complications in patients undergoing implantation of the Boston keratoprosthesis. He now performs corneal crosslinking (CXL) on the carrier donor tissue of the Boston keratoprostheses and on the corneal pocket tissue prior to implantation of the KeraKlear device. “CXL pre-treatment of the host cornea can reduce the possibility of future corneal melt and make the implant fit more tightly in the pocket,” he added. A John Kanellopoulos: ajk@brilliantvision.com