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F. Gekeler, M. Rohrbach, P. Szurman, D. Besch, E. Zrenner, K. Bartz-Schmidt, H. G. Sachs; Active Subretinal Implants - Explantation Procedures in 11 Volunteers and Histological Results. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2025. doi: https://doi.org/.
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Electronic retinal implants require external energy to stimulate retinae of patients suffering from degenerative diseases such as retinitis pigmentosa (RP). We report on the surgical feasibility of the intra- and extra-ocular explantation procedures. Furthermore, we present histological changes observed in surrounding orbital tissue.
In total, we have operated 11 volunteers with RP. The implant (3 x 3 x 0.1 mm) consisting of 1500 microphotodiodes, amplifiers and TiN electrodes was located subretinally in the foveal region. A trans-sclerally, trans-choroidally implanted polyimide foil carries connection wires to the lateral orbital rim where it is fixated and connected to a silicone cable. The silicone cable is implanted subperiostally beneath the temporal muscle using a trocar to the retro-auricular space. Devices were explanted between 4 weeks and 4 months (one patient refused explantation). Histology was performed on specimens obtained from orbital tissue.
All explantations were performed as planned without adverse events. Although the extraocular parts of the implant in the orbit were sometimes strongly walled in by fibrous tissue, the inert material was never adherent to it, thereby allowing easy retraction of the implant through this "tunnel." Removal from the subretinal space did not require intraocular procedures; as there were only very minor retinal tissue reactions, the implant could simply be retracted with silicon oil in place. - Histologically, the connective orbital tissue was condensed along the extra-bulbar implant. Moderate inflammatory reactions consisting of CD4, CD 8, and especially CD68 positive cells along the extra-bulbar implant were observed. Foreign body cells were seen only occasionally.
Explantation of the active subretinal device with a trans-scleral, trans-choroidal cable connection to an extra-corporeal connector was uneventful. Inflammatory tissue alterations were moderate making explantation surgery manageable and possibly allowing re-implantation of devices in the same region.
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