gms | German Medical Science

Objective: To compare two different epiretinal stimulation implants after implantation of the EPIRET III prototype and the ARGUS II system in patients with retinitis pigmentosa.

Materials and Methods: Six blind individuals with retinitis pigmentosa underwent the implantation of an EPIRET III prototype in the context of a phase I/IIa trial as proof of concept in man with explantation after 4 weeks. 5 other RP patients received an ARGUS II system as permanent therapeutical device with a follow-up of 6 months. Two of these patients received the EPIRET device in one eye and the ARGUS II later on in the other. The EPIRET III prototype is a completely intraocular device which was test under laboratory conditions with an experimental signal transfer and no camera device. The ARGUS II system is an epiretinal stimulator with an extraocular power supply that is used with a camera and a video processor unit. Different features of the implantation procedures and the stimulation properties such as stimulation thresholds were compared.

Results: The implantation of the EPIRET III device took 2 hours, the implantation of the ARGUS II device 2,0 – 4 hours. One patient complained of chronic periocular pain after implantation of the ARGUS device, another patient had a sterile hypopion after EPIRET III implantation. The intraindividual comparison of stimulation thresholds in the binocular patients yielded that the EPIRET device required amplitudes of 10 and 6 μA with charge densities of 56,81 and 15,51 μC/cm2 at a stimulation duration of 446 ms, whereas the ARGUS device required amplitudes of 473,66 and 373 μA with charge densities of 737,68 and 570,75 μC/cm2, respectively, at a duration of 450 ms.

Discussion: Possible explanations for the lower thresholds in the EPIRET device maybe a closer contact due to the fixation with 2 tacks instead of 1, the 3D configuration of the EPIRET electrodes or the coating with IrOxact and a resulting high surface magnification.