Threshold suprachoroidal-transretinal stimulation current required by different-size electrodes in rabbit eyes.
OBJECTIVE
To evaluate the threshold currents required by different-size electrodes under various stimulus parameters by suprachoroidal-transretinal stimulation (STS) in rabbit eyes.


METHODS
An electrode array with 4 differently sized electrode contacts (50, 150, 350 and 500 μm in diameter) was implanted into the suprachoroidal space of the rabbit eyes. The electrically evoked potential was recorded extradurally on the visual cortex, and the threshold was measured for each size electrode by a biphasic current pulse at the pulse durations of 0.25, 0.5, 0.75 and 1.0 ms. Stimuli were applied at 1, 2 and 4 Hz.


RESULTS
The current thresholds with the 50-μm electrode were 80 ± 21.2 and 41.4 ± 6.5 μA for 0.25- and 1.0-ms pulses, respectively. That obviously exceeded the limits for safe stimulation with platinum. Compared to 350- and 500-μm electrodes, a lower threshold can be obtained by the 150-μm electrode just at 1 Hz. And the most significant change in the threshold as the stimulus frequency increased to 4 Hz was obtained by the 150-μm electrode with short-duration pulse (0.25 ms).


CONCLUSIONS
The large surface electrode with long-duration pulses may be preferable for the STS prosthesis. And stimuli with low frequency are suggested to be the safer choice.
Liang
Ting
T
Department of Ophthalmology, Second Affiliated Hospital of Harbin Medical University, Harbin, China.
Zhao
Liming
L
Sui
Xiaohong
X
Zhou
Chuanqing
C
Ren
Qiushi
Q
Qi
Yanhua
Y
D000818:Animals; D002829:Choroid / Q000502:physiology*; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D005074:Evoked Potentials, Visual / Q000502:physiology*; D008839:Microelectrodes; D019736:Prostheses and Implants; D011817:Rabbits; D012160:Retina / Q000502:physiology*; D012684:Sensory Thresholds; D014793:Visual Cortex / Q000502:physiology*