Surgical Procedure for Subretinal Implants With External Connections: The Extra-Ocular Surgery in Eight Patients

Abstract

Purpose: : Subretinal implants require external energy to stimulate degenerated retinae successfully, e.g. in retinitis pigmentosa (RP). We report on a newly developed surgical approach for transchoroidal, transorbital implantation of such devices with connections from the subretinal space to the retro-auricular region.

Methods: : Implants comprise two entities: a 1550 microphotodiode-array and a 4*4 electrode array (for light-independent stimulation). Implants receive energy and signals via a transchoroidally implanted polyimide foil. After scleral penetration the foil is fixated episclerally with a fixation pad; it then passes under the lateral lid to the lateral orbital rim where it is fixated with sutures through holes in the lateral orbital bone; in the temporal fossa it is connected to a silicone cable which is implanted subperiostally beneath the temporal muscle using a trocar to the retro-auricular space where it penetrates the skin. In the retro-auricular space a basal plate (surgical steel) is screwed into two bone holes in the scull and the silicone cable is clamped using a cover plate. - 8 human volunteers with RP were implanted for 4 weeks (as required by the local ethics committee).

Results: : All implantations could be performed without complications; implants were intact and electrically functioning postoperatively. Localized edema and hemorrhages in operated areas resolved within days. Fixation of the implants was stable through the entire study. The permanent skin penetration proved to be uncomplicated. Postoperatively, motility was minimally restricted in downgaze and ab-/adduction but decreased in the course. Explantation was uneventful; however the implant had to be dissected for this.

Conclusions: : The above described procedure proved to be successful in all cases and led to minimal discomfort. A permanent transchoroidal and transcutaneous passage for external energy supply seems to be a feasible implantation method until totally implantable and wireless systems are available and function properly. The method is of potential interest for all kinds of epi- or subretinal implantss, for optic nerve stimulation devices and other ocular implants which require chronic external cable connections.

Keywords: retinal degenerations: hereditary • clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials • vitreoretinal surgery