Evaluation of electrochemically treated bulk electrodes for a retinal prosthesis by examination of retinal intrinsic signals in cats.
OBJECTIVE
Our goal was to determine the feasibility of using electrochemically treated bulk platinum electrodes with large charge injection capacity for a retinal prosthesis.


METHODS
Seven eyes of seven cats were studied. Small retinal areas were focally stimulated with electrochemically treated bulk electrodes (φ = 500 µm) placed in a scleral pocket. Fundus images with near-infrared (800-880 nm) light were recorded, and a 2D map of the reflectance changes elicited by the electrical currents was constructed by subtracting the images taken before stimulation from those taken after stimulation. The impedance of each electrode was measured at 1 kHz. The degree of retinal elevation by the electrode was measured by optical coherence tomography. Scleral thickness where the electrode array was inserted was measured in histologic sections.


RESULTS
The diameter of reflectance changes (full width at half maximum) was 0.42 ± 0.22 mm [mean ± standard deviation (SD)] in minor axes and 1.46 ± 0.82 mm in major axes. The threshold current decreased with a reduction in the residual scleral thickness (R (2) = 0.9215; P = 0.0002); it also decreased with an increase in retinal elevation (R (2) = 0.6259; P = 0.0111).The threshold current also decreased with an increase in electrode impedance (R (2) = 0.2554; P = 0.0147).


CONCLUSIONS
Electrochemically treated porous platinum electrodes can stimulate localized retinal areas. The threshold current necessary to stimulate the retina was influenced by residual scleral thickness and the electrode tightness of fit against the sclera.
Department of Applied Visual Science, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka, 565-0871, Japan.
Hiroyuki
H
Kanda
Toshifumi
T
Mihashi
Tomomitsu
T
Miyoshi
Yoko
Y
Hirohara
Takeshi
T
Morimoto
Yasuo
Y
Terasawa
Takashi
T
Fujikado
D000818:Animals; D002415:Cats; D003952:Diagnostic Imaging; D017097:Electric Impedance; D004558:Electric Stimulation; D055664:Electrochemical Techniques; D004567:Electrodes, Implanted; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D008297:Male; D008839:Microelectrodes; D009897:Optic Chiasm / Q000502:physiology; D010775:Photic Stimulation; D012160:Retina / Q000502:physiology*; D041623:Tomography, Optical Coherence; D057488:Visual Prosthesis