Modifications of Subretinal Surgery to Implant an Active Subretinal Microphotodiode Array

Abstract

Purpose: : Subretinal implants intend to replace degenerated photoreceptors in diseases such as retinitis pigmentosa (RP) by electrically stimulating remaining retinal cells. Additional energy for microphotodiode arrays (MPDA) is delivered by a transsclerally / transchoroidally implanted polyimide (PI) foil. Placement of the device has to be optimal due to areas of different retinal susceptibility to electrical stimulation and be calculable. - We report on a technique to determine the direction and distance of placement, new guiding instruments and a method to implant under direct visualization of the fundus.

Methods: : Before the flexible PI foil can be forwarded in the subretinal space a stiffer guiding foil (50 µm; polyethylene terephthalate) is temporarily placed. Three differently shaped tips (sharp, semi-sharp, round) were tested; the foil was colored blue for better visibility and equipped with length markings. Angle and length of implantation were calculated based on MRI scans of the eyes and 3 D computer-modelling. The foil was inserted into the scleral/choroidal opening and then forwarded under fundus visualization using a wide-field contact lens system. The new method has thus far been tested in 2 patients.

Results: : The semi-sharp tip has shown to be the best compromise between ease of protrudement, opening up the subretinal space, and prevention of malpositioning (e.g. supra-choroidally) and retinal perforations. Direct visualization of the colored guiding foil advancing in the subretinal space proved to be feasible in all cases. Calculations were accurate for the angle and deviated max. 4 mm.

Conclusions: : Placement of the MPDA under direct visualization required sophisticated manoeuvres, but desired positions could be reached in all cases. While the colored foil and the pre-operative calculations clearly proved advantageous, direct fundus visualization has to prove its superiority compared to our previously described technique (Sachs et al, ARVO 2007).

Clinical Trial: : www.clinicaltrials.gov NCT00515814

Keywords: retina • vitreoretinal surgery • retinitis