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J. Menzel-Severing, B. Sellhaus, G. Roessler, B. Hermanns-Sachweh, P. Walter, EPI-RET3 Study Group; Histomorphological and Immunohistochemical Changes to the Retina Following Implantation and Explantation of an Inactive Epiretinal Visual Prosthesis in Minipigs. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3028.
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An intraocular device that allows for wireless transfer of energy and information to 25 epiretinal stimulation electrodes has been developed and was successfully implanted and explanted in minipigs. Histologic slides from the study eyes were obtained to investigate histomorphologic changes to the retina which may have been induced by the surgery, the implant or the retinal tacks used for fixation. Detection and characterization of any such changes induced by the implant or after its removal are crucial since they may potentially interfere with function and safety of the device.
5 minipigs were equipped with an inactive epiretinal prosthesis type EPI-RET3. The receiver coil of the device was placed into the capsular bag, while the stimulator unit was placed on the posterior pole and fixated using retinal tacks. The prosthesis was left in place for 4 weeks. Subsequently the implantation steps were reversed to remove the item. After another postoperative period of 4 weeks the eyes were enucleated for histopathologic exam.We obtained HE-stained slides from specimens embedded in paraffin. In addition, we conducted immunohistochemical preparation using LCA and CD68 antibodies to visualize immunocompetent cells and GFAP to search for glial cell proliferation. Other samples were plastinated to allow for a grinding technique to visualize the solid retinal tacks in conjunction with the soft retinal tissue.
HE staining revealed minor alteration of retinal tissue, showing a moderate degree of cystic disaggregation; modification of cell layers could not be observed.In immunohistochemistry, increased staining of Mueller cells suggests a moderate glial cell activation, while inflammatory cells are absent as in normal retina.Using the grinding technique, tissue in close proximity to the retinal tacks showed to be unchanged and presented no cellular reaction to the fixation trauma.
The surgical interventions for implantation and explantation as well as the visual prosthesis itself do not produce any noxious inflammatory effects in the retinal tissues. Minor changes found in Mueller cells are not limited to areas adjacent to the implant but are ubiquitous. Hence, we believe this to be a non-specific, reversible reaction to the vitreoretinal surgery.The findings suggest for the device to be sufficiently safe from a histopathologic point of view as to be further examined clinically.
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