Improvement of the osteo-odonto-keratoprosthesis according to Strampelli: influence of diameter of PMMA cylinder on visual field.

Abstract

In surgical management of severe corneal scarring, the osteo-odonto-keratoprosthesis (OOKP) according to Strampelli is recognised as the best choice. Nevertheless, the patients are handicapped by a restricted visual field. Enlarging the optical cylinder diameter should allow better rehabilitation of the patients. A mathematical model to calculate the theoretical maximum visual field according to the length and the diameter of the cylinder of a keratoprosthesis was developed. The theoretical values were compared with our findings in three OOKP patients operated on in our hospital. The theoretical extent of the visual field with a cylinder of 8 mm length is 55 deg if the diameter is 3 mm and 62 deg if the diameter is 3.5 mm. The visual fields of our OOKP patients in both types of keratoprosthesis are, however, below the theoretically calculated values. Implantation of a prosthesis with a diameter of 3 mm produced horizontal visual fields of 30 and 36 deg in two patients. In one patient with a prosthesis diameter of 3.5 mm the field was 53 deg. The diameter of the visual field increases with the diameter and decreases with increasing length of the optical cylinder. In OOKP the implantation of a PMMA cylinder with a diameter of 3.5 mm is possible. The enlargement of the diameter of the optical cylinder leads to significant enlargement of the visual field. The size of the cylinder is limited by the diameter of the available root of the tooth.