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H. G. Sachs, U. Brunner, F. Gekeler, K.-U. Bartz-Schmidt, V.-P. Gabel, W. Wrobel, A. Hekmat, E. Zrenner; The Development of a Guiding Tool for Transchoroidal Subretinal Chip Implantation to Protect the Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4045.
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The protection of the retina during a transchoroidal implantation procedure is mandatory. Due to the fact that there is no visibility of the retinal situation while the implant is placed a protective shield is advantageous. The aim was a minimal traumatic implantation of a 3mm wide cable-bound chip with a transchoroidal connecting cable.
In experiments with laboratory animals the requirements for the material,dimensions and shape of the shielding guide were determined. A method of preparation of the choroid was developed to have an almost bloodless penetration of the choroid. Different prototypes of guiding foils were tested and served as implantation instruments in 22 implantations in domestic pigs. These prototypes were optimized in geometry, material and stability to achieve an instrument which could be used in human implantations. The final design was tested in 7 implantations in humans.
The optimized foil structure was stable enough to mechanically separate retina from underlying RPE. Too soft and thin materials are contraproductive in the implantation process. Transparent material is advantageous to observe the retinal behaviour during the implantation at the site of choroidal penetration. Optimal performance was achieved with 50 µm transparent Polypropylen with lance shaped tip. Retinal prolapse through the choroidal window was prevented from in all human implantations. Radiodiathermy proved ideal to prevent the choroid from bleeding during the implantation in animal and humans.
With this instrument a minimal traumatic implantation of subretinal devices can be achieved. Transchoroidal surgery for chip implantation is manageable and made easy by this device and by the use of radiodiathermy. The experience of the requirements for a transchoroidal procedure could be of potential interest for other applications targeting the subretinal or subchoroidal space e.g. drug delivery.
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