Neuroprotective effect of subretinal implants in the RCS rat.
OBJECTIVE
Retinal prosthetics have been designed to interface with the neural retina by electrically stimulating the remaining retinal circuits after photoreceptor degeneration. However, the electrical stimulation provided by the subretinal implant may also stimulate neurotrophic factors that provide neuroprotection to the retina. This study was undertaken to determine whether electrical stimulation from a subretinal photodiode-based implant has a neuroprotective effect on photoreceptors in the RCS rat, a model of photoreceptor degeneration.


METHODS
Eyes of RCS rats were implanted with an active or inactive device or underwent sham surgery before photoreceptor degeneration. Outer retinal function was assessed with electroretinogram (ERG) recordings weekly until 8 weeks after surgery, at which time retinal tissue was collected and processed for morphologic assessment, including photoreceptor cell counts and retinal layer thickness.


RESULTS
At 4 to 6 weeks after surgery, the ERG responses in the active-implant eyes were 30% to 70% greater in b-wave amplitude than the responses from eyes implanted with inactive devices, those undergoing sham surgery, or the nonsurgical control eyes. At 8 weeks after surgery the ERG responses from active-implant eyes were not significantly different from the control groups. However, the number of photoreceptors in eyes implanted with the active or inactive device was significantly greater in the regions over and around the implant versus sham-surgical and nonsurgical control eyes.


CONCLUSIONS
These results suggest that subretinal electrical stimulation provides temporary preservation of retinal function in the RCS rat. In addition, implantation of an active or inactive device into the subretinal space causes morphologic preservation of photoreceptors in the RCS rat until 8 weeks after surgery. Further studies are needed to determine whether the correlation of neuropreservation with subretinal implantation is due to electrical stimulation and/or a mechanical presence of the implant in the subretinal space.
Pardue
Machelle T
MT
Atlanta VA Medical Center, Decatur, GA 30033, USA. mpardue@emory.edu
Phillips
Michael J
MJ
Yin
Hang
H
Sippy
Brian D
BD
Webb-Wood
Sarah
S
Chow
Alan Y
AY
Ball
Sherry L
SL
D000818:Animals; D002452:Cell Count; D004195:Disease Models, Animal; D004599:Electric Stimulation Therapy / Q000379:methods*; D004567:Electrodes, Implanted; D004596:Electroretinography; D018696:Neuroprotective Agents; D020419:Photoreceptor Cells, Vertebrate / Q000473:pathology; D019736:Prostheses and Implants; D019919:Prosthesis Implantation; D051381:Rats; D011922:Rats, Mutant Strains; D012160:Retina / Q000503:physiopathology* / Q000601:surgery; D012162:Retinal Degeneration / Q000503:physiopathology / Q000517:prevention & control*
D018696:Neuroprotective Agents