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Ajit B. Majji, Mark S. Humayun, James D. Weiland, Satoshi Suzuki, Salvatore A. D’Anna, Eugene de Juan; Long-Term Histological and Electrophysiological Results of an Inactive Epiretinal Electrode Array Implantation in Dogs. Invest. Ophthalmol. Vis. Sci. 1999;40(9):2073-2081.
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purpose. Short-term pattern electrical stimulation of the retina via
multielectrode arrays in humans blind from photoreceptor loss has shown
that ambulatory vision and limited character recognition is possible.
To develop an implantable retinal prosthesis that would provide useful
vision, these results need to be sustained over a prolonged period of
retinal electrical stimulation. As a first step toward this goal,
the biocompatibility and the feasibility of surgically
implanting an electrically inactive electrode array onto the retinal
surface was tested.
methods. A 5 × 5 electrode array (25 platinum disc–shaped electrodes in a
silicone matrix) was implanted onto the retinal surface using retinal
tacks in each of the 4 mixed-breed sighted dogs. Color fundus
photography, fluorescein angiography, electroretinography, and visual
evoked potentials were obtained preoperatively, at 1-week intervals for
2 weeks postoperatively, then at 2-week intervals up to 2 months
postoperatively, and thereafter at 1-month intervals. One dog was
killed at 2 months after implantation and a second dog after 3 months
of implantation. Histologic evaluation of the retinas was performed.
The remaining two dogs continue to be followed beyond 6 months after
the implantation surgery.
results. No retinal detachment, infection, or uncontrolled intraocular bleeding
occurred in any of the animals. Retinal tacks and the retinal array
remained firmly affixed to the retina throughout the follow-up period.
Hyperpigmentation of the retinal pigment epithelium was observed only
around the site of retinal tack insertion. No fibrous encapsulation of
the implant or intraocular inflammation was visible. A- and b-wave
amplitudes of the electroretinogram were depressed at the first
postoperative week testing but recovered over the ensuing 1 week and
were not statistically different from the normal unoperated fellow eye
throughout the postoperative period. N1 and P1 wave amplitudes of the visual evoked potentials were not significantly
different from the normal fellow eyes at any of the postoperative test
intervals. Fluorescein angiography showed that the entire retina
including the area under the electrode array remained well perfused.
Similarly, histologic evaluation revealed near total preservation of
the retina underlying the electrode array.
conclusions. Implantation of an electrode array on the epiretinal side (i.e., side
closest to the ganglion cell layer) is surgically feasible, with
insignificant damage to the underlying retina. The platinum and
silicone arrays as well as the metal tacks are biocompatible. With the
success of implanting an electrically inactive device onto the retinal
surface for prolonged periods, the effects of long-term retinal
electrical stimulation are now ready to be tested as the next step
toward developing a prototype retinal prosthesis for human
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