Electrophysiological studies of the feasibility of suprachoroidal-transretinal stimulation for artificial vision in normal and RCS rats.
OBJECTIVE
Assessment of a novel method of retinal stimulation, known as suprachoroidal-transretinal stimulation (STS), which was designed to minimize insult to the retina by implantation of stimulating electrodes for artificial vision.


METHODS
In 17 normal hooded rats and 12 Royal College of Surgeons (RCS) rats, a small area of the retina was focally stimulated with electric currents through an anode placed on the fenestrated sclera and a cathode inserted into the vitreous chamber. Evoked potentials (EPs) in response to STS were recorded from the surface of the superior colliculus (SC) with a silver-ball electrode, and their physiological properties and localization were studied.


RESULTS
In both normal and RCS rats, STS elicited triphasic EPs that were vastly diminished by changing polarity of stimulating electrodes and abolished by transecting the optic nerve. The threshold intensity (C) of the EP response to STS was approximately 7.2 +/- 2.8 nC in normal and 12.9 +/- 7.7 nC in RCS rats. The responses to minimal STS were localized in an area on the SC surface measuring 0.12 +/- 0.07 mm(2) in normal rats and 0.24 +/- 0.12 mm(2) in RCS rats. The responsive area corresponded retinotopically to the retinal region immediately beneath the anodic stimulating electrode.


CONCLUSIONS
STS is less invasive in the retina than stimulation through epiretinal or subretinal implants. STS can generate focal excitation in retinal ganglion cells in normal animals and in those with degenerated photoreceptors, which suggests that this method of retinal stimulation is suitable for artificial vision.
Kanda
Hiroyuki
H
Department of Physiology and Biosignaling, Graduate School of Medicine, Osaka University, Suita, Japan.
Morimoto
Takeshi
T
Fujikado
Takashi
T
Tano
Yasuo
Y
Fukuda
Yutaka
Y
Sawai
Hajime
H
D000818:Animals; D002829:Choroid / Q000502:physiology*; D004558:Electric Stimulation; D004599:Electric Stimulation Therapy / Q000379:methods*; D004567:Electrodes, Implanted; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005240:Feasibility Studies; D008297:Male; D008839:Microelectrodes; D009900:Optic Nerve / Q000601:surgery; D010775:Photic Stimulation; D051381:Rats; D020318:Rats, Long-Evans; D011922:Rats, Mutant Strains; D012160:Retina / Q000502:physiology*; D012162:Retinal Degeneration / Q000503:physiopathology*; D013477:Superior Colliculi / Q000502:physiology*