中文摘要：

基于刺入式电极的视神经视觉假体，为盲人的视觉修复提供了新的可能性。为了对该视神经假体的电刺激策略和微电极设计提供理论支持，基于真实的电极结构，在COMSOL软件中建立刺入式微电极的外部电场仿真模型，并将其与利用NEURNO软件实现的神经纤维双层电缆模型结合，系统地研究电极与视神经纤维的相对位置、电刺激脉冲宽度以及电极几何结构的改变对视神经纤维兴奋阈值的影响。不同电极位置、刺激脉宽刺激下阈值变化规律的仿真结果，与以往报道的动物实验和仿真实验结果相符，证明了所建模型的有效性。根据仿真结果，对刺入式视神经假体中刺激脉宽的选择和电极几何结构的设计，建议如下：窄脉宽刺激有利于降低能量消耗；电极锥度的设计要在满足电极力学特性及易于植入视神经的基础上，尽可能地减小，以降低纤维兴奋的阈值；电极的暴露面积越小，纤维兴奋所需的电流阈值越低，但电荷密度阈值越高；较低的电流阈值有利于减少能量消耗，但过高的电荷密度阈值却容易造成组织损伤，因此电极暴露面积的设计需要在耗能与安全性之间进行综合考虑。电极绝缘层厚度的改变对视神经纤维的兴奋阈值没有明显的影响，但从电极插入的难易考虑，应尽可能减小绝缘层厚度。以上结果对人体其他部位神经纤维的电刺激同样具有参考价值。

英文摘要：

A visual prosthesis based on penetrating electrode stimulation within the optic nerve （ON） is a potential way to restore partial functional vision for the blind patients. In order to provide theoretical basis for electrical stimulation strategies and the electrode design of above-mentioned visual prosthesis, a finite-element model of the electric field generated by an actual penetrating microeleetrode was constructed in COMSOL, and then coupled to the multi-compartment cable model of the optic nerve fiber implemented using NEURON. With this method, we evaluated the effects of stimulating electrode location, pulse duration of electrical stimulus and electrode structure on the excitation thresholds of optic nerve fibers. Simulation results showed that the impact of the former two factors on the fiber thresholds agreed with that reported in previous animal and simulation studies, which demonstrated the effectiveness of our models. The following suggestions about the design of stimulus pulse duration and electrode structure of the penetrative ON prosthesis were also obtained according to our simulation work. Stimulus with narrow pulse width helps reduce energy consumption. The electrode taper should be designed as small as possible to lower the threshold but should not disturb the electrode insertion. Decreasing the electrode exposed area helps lower the current threshold and therefore reduces the power consumption, but it also increases the charge density threshold, which eases to result in electrochemical damage to ON. Thus, the electrode exposed area should be designed appropriately to avoid excessive power consumption and tissue damage. Changing the coating thickness of the electrode has no significant effect on the fiber threshold, but a electrode with thin coating is recommended to decrease the insertion difficulty. These results are also of valuable reference to the electrical stimulation of other nerve fibers of human body.