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Qiushi Ren, Menghui Li, Yan Yan, Liming Li; Simulating current focusing and steering in penetrative optic nerve stimulation: a computational model. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1041.
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© ARVO (1962-2015); The Authors (2016-present)
A visual prosthesis based on penetrative optic nerve (ON) stimulation is a potentail way for vision recovery. The fact that an enormous number of RGC axons of various diameters are tightly packed in mammalian optic nerve makes it difficult to implant more numbers of stimulating electrodes. Here we presented a computational model to simulate and evaluate two widely used field shaping strategies, current steering and current focusing, in penetrative stimulation of rabbit ON.
Finite element models with were established to compute the 3D electric potential distribution generated with different stimulating parameters under 2 and 3-electrode configurations. Then the external electric potential was fed to a large number of randomized multi-compartment cable models to calculate the membrane potential of each ON fibre to predict whether AP could be elicited in each sampled position. Finally a statistical process was conducted to quantify the recruitment region and three indicators were statistically derived to evaluate effects of current steering and current focusing.
The shifting rate (SR) value of the 2-electrode configuration showed consistent correlation to the steering coefficient, whereas no such significant correlation could be detected in that of the 3-electrode configuration. For the 3-electrode configuration, large values of compensation coefficient resulted in a large recruitment area in the (ON) under arbitrary stimulus amplitude, which was contrary to the intention of current focusing. Both configurations demonstrated rather localized neural fibre recruitment compared with the surface ON stimulation.
The simulation results show that the 2-electrode configuration excels in current steering whereas the 3-electrode configuration performs poorly in both current steering and focusing. The localized recruitment of both configurations implies that current focusing might be unnecessary in penetrative optic nerve stimulation.
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