gms | German Medical Science

IrOx-film-electrodes are a possible choice for stimulation microelectrodes of a projected retina implant. The aim of this study was to examine parameters of epiretinal electrical stimulation and their tissue compatibility.

In 12 minipigs vitrectomy of the right eye was performed under general anaesthesia. A polyimide based microcontact film (MCF) with eleven IrOx electrodes was inserted through a scleral port, placed epiretinal, fixed by perfluordecaline (PFCL) and connected by a cable to an external electrical stimulator. The retinae were stimulated with standardized programs for 4 hours with different charges: group (gr) 1-4 with 0, 0.5, 1 and 4 mC/cm² (n = 3). After removal of the MCF and PFCL animals were observed for a period of 14 days. Postoperative examination to observe retinal changes due to insertion and/or stimulation was followed by comparison to each untreated left eye and to gr 1. After sacrificing the eyes were enucleated and worked off histologically.

We noticed sporadic reversible punctiform bleeding of the retina during implantation. Post-stimulation examination showed in 2 eyes of gr 4 strong edema in the stimulated area. After 2 weeks we found in each gr 1-3 sporadic pigment coating in the stimulated area. Two eyes of gr 4 showed local pale retina. Histological evaluation of the stimulated area revealed no structural changes in any treatment of gr 1-3. In one eye of gr 4 there was an arcuated structure of the retina which is correlated to the observed edema.

Charges of up to 1 mC/cm² are applicable to retinal tissue in a time range of 4 hours without expecting a significant damage of the retina, if administered by IrOx-electrodes. Our stimulation parameters and MCF with IrOx-electrodes are suitable for electrical stimulation of the human retina so that this study represents an important preparatory work for a further development of the retina implant.