The "Aachen" keratoprosthesis: a new approach towards successful keratoprosthesis-surgery

Background. None of the keratoprostheses available today is absolutely succ essful in the long term, neither the problems of extrusion, retroprosthetic membrane formation and intraocular pressure rise are yet solved. A new typ e of keratoprosthesis is required which can show improved ingrowth characte ristics and allow Intraocular pressure measurements. In order to possibly m eet the above mentioned requirements we developed a flexible silicone kerat oprosthesis with scleral fixation and chemical surface modification. Methods. The one-piece keratoprosthesis is made of silicone rubber. Its opt ical zone has a diameter of 11 mm and is 0.3 mm thick. The surface-modified haptic consists of a scleral rim and eight branches for scleral fixation. A ridge at the back of the keratoprosthesis fitting into the trephination h ole shall avoid leakage and retroprosthetic membrane formation. Optical and mechanical qualities are characterised by tensile tests, spectrophotometry and topography. Results. A method for keratoprosthesis-production was established. The opti cal quality of the device was improved by submicron lathing of the mould. S pectrophotometry showed high visible and ultraviolet light transmission of the silicone. Mechanical tests with silicone samples revealed high tensile strength and elongation at break. The mechanical properties were not impair ed by surface modification. Conclusions. The production of a flexible silicone keratoprosthesis with hi gh optical and mechanical properties was established. Its use both for the treatment of permanently opacified corneas and as temporary keratoprosthesi s seems to be possible.