Threshold Suprachoroidal-Transretinal Stimulation Current Required by Different-Size Electrodes in Rabbit Eyes

Aims: 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 mu m 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-mu m electrode were 80 +/- 21.2 and 41.4 +/- 6.5 mu A for 0.25- and 1.0-ms pulses, respectively. That obviously exceeded the limits for safe stimulation with platinum. Compared to 350- and 500-mu m electrodes, a lower threshold can be obtained by the 150-mu m 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-mu m electrode with short-duration pulse (0.25 ms). Conclusion: 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. Copyright (C) 2010 S. Karger AG, Basel