Ab. Majji et al., Long-term histological and electrophysiological results of an inactive epiretinal electrode array implantation in dogs, INV OPHTH V, 40(9), 1999, pp. 2073-2081
PURPOSE. Short-term pattern electrical stimulation of the retina via multie
lectrode arrays in humans blind from photoreceptor loss has shown that ambu
lator; vision and limited character recognition is possible. To develop an
implantable retinal prosthesis that would provide useful vision, these resu
lts need to be sustained over a prolonged period of retinal electrical stim
ulation. As a first step toward this goal, the biocompatibility and the fea
sibility of surgically implanting an electrically inactive electrode array
onto the retinal surface was tested.
METHODS. A 5 x 5 electrode array (25 platinum disc-shaped electrodes in a s
ilicone matrix) was implanted onto the retinal surface using retinal tacks
in each of the 4 mixed-breed sighted dogs. Color fundus photography, fluore
scein angiography, electroretinography, and visual evoked potentials were o
btained preoperatively, at 1-week intervals for 2 weeks postoperatively, th
en 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 se
cond dog after 3 months of implantation. Histologic evaluation of the retin
as was performed. The remaining two dogs continue to be followed beyond 6 m
onths after the implantation surgery.
RESULTS. No retinal detachment, infection, or uncontrolled intraocular blee
ding occurred in any of the animals. Retinal tacks and the retinal array re
mained firmly affixed to the retina throughout the follow-up period. Hyperp
igmentation 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 elect
roretinogram were depressed at the first postoperative week testing but rec
overed over the ensuing 1 week and were not statistically different from th
e normal unoperated fellow eye throughout the postoperative period. N-1 and
P-1 wave amplitudes of the visual evoked potentials were not significantly
different from the normal fellow eyes at any of the postoperative test int
ervals. Fluorescein angiography showed that the entire retina including the
area under the electrode array remained well perfused. Similarly, histolog
ic 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 in
significant damage to the underlying retina. The platinum and silicone arra
ys as well as the metal tacks are biocompatible. With the success of implan
ting an electrically inactive device onto the retinal surface for prolonged
periods, the effects of long-term retinal electrical stimulation are now r
eady to be tested as the next step toward developing a prototype retinal pr
osthesis for human use.