Electrical stimulation of isolated retina with microwire glass electrodes.
The development of high-resolution retinal prostheses fabricated from silicon wafers presents an interesting problem: how to electrically bridge the space between the flat silicon wafer and the curved retinal surface. One potential "bridge" is a microwire glass electrode. In this paper we present our results in evaluating microwire glass electrodes. We stimulated isolated rabbit retina (n = 5) with a 0.0256 cm(2) microwire electrode. The current and pulse duration were varied from 498 to 1660 microA and 0.1 to 3 ms, respectively. We found that short pulses produced more spikes per coulomb and longer pulses produced more spikes per milliamp. The optimal pulse duration range of 0.7-1 ms was identified as a compromise between the advantages of short and long pulses. Stimulation of isolated rabbit retina with microwire glass results in consistent neuronal spike formation at safe charge density, 20.7 +/- 4.3 microC/cm(2). We also examined the response of retinas (n = 6) to stimulation with a smaller microwire electrode, 0.0002 cm(2). We found that less current was required (15 microA versus 756 microA) for a 1 ms pulse, but at the expense of greater charge density (75 microC/cm(2) versus 29.5 microC/cm(2)). Nonetheless, a 128-fold reduction in area resulted in only a 2.7-fold increase in charge density required for a 1 ms pulse duration. The results presented here indicate that microwire glass can be used as a neural stimulating electrode to bridge the gap between flat microelectronic stimulator chips and curved neuronal tissue.
Johnson
Lee
L
Naval Research Laboratory, Washington, DC, USA. ljj@ccs.nrl.navy.mil
Perkins
F Keith
FK
O'Hearn
Thomas
T
Skeath
Perry
P
Merritt
Charles
C
Frieble
Joseph
J
Sadda
Srinivas
S
Humayun
Mark
M
Scribner
Dean
D
D000818:Animals; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods*; D004566:Electrodes; D005071:Evoked Potentials / Q000502:physiology; D005898:Glass; D066298:In Vitro Techniques; D008855:Microscopy, Electron, Scanning / Q000379:methods; D011817:Rabbits; D012160:Retina / Q000528:radiation effects*; D012684:Sensory Thresholds; D013997:Time Factors