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

Background: In surgical management of severe corneal scarring, the osteo-od onto-keratoprosthesis (OOKP) according to Strampelli is recognised as the b est choice. Nevertheless, the patients are handicapped by a restricted visu al field. Enlarging the optical cylinder diameter should allow better rehab ilitation of the patients. Patients and methods: A mathematical model to ca lculate the theoretical maximum visual field according to the length and th e diameter of the cylinder of a keratoprosthesis was developed. The theoret ical values were compared with our findings in three OOKP patients operated on in our hospital. Results: The theoretical extent of the visual field wi th a cylinder of 8 mm length is 55 deg if the diameter is 3 mm and 62 deg i f the diameter is 3.5 mm. The visual fields of our OOKP patients in both ty pes of keratoprosthesis are, however, below the theoretically calculated va lues. Implantation of a prosthesis with a diameter of 3 mm produced horizon tal visual fields of 30 and 36 deg in two patients. In one patient with a p rosthesis diameter of 3.5 mm the field was 53 deg. Conclusions: The diamete r of the visual field increases with the diameter and decreases with increa sing length of the optical cylinder. In OOKP the implantation of a PMMA cyl inder with a diameter of 3.5 mm is possible. The enlargement of the diamete r of the optical cylinder leads to significant enlargement of the visual fi eld. The size of the cylinder is limited by the diameter of the available r oot of the tooth.