The visual system has one of the most complex structures of all sensory systems and is perhaps the most important sense for everyday life. Its functional organization was extensively studied for decades in animal and humans, for example by correlating circumscribed anatomical lesions in patients with the resulting visual dysfunction. During the past two decades, significant achievements were accomplished in characterizing and modulating visual information processing using non-invasive stimulation techniques of the normal and damaged human eye and brain. Techniques include transcranial magnetic stimulation (TMS) and low intensity electric stimulation using either direct or alternating currents applied transcranially (tDCS or tACS) near or above the visual cortex, or alternating currents applied transorbitally (trACS). In the case of transorbital stimulation of the visual system the electrodes are attached near the eye, to the eyelids (transpalpebral electrical stimulation - TPES) or the cornea (tanscorneal electrical stimulation TcES). Here, we summarize the state-of-the-art of visual system magnetic and electric stimulation as a method to modulate normal vision, induce brain plasticity, and to restore visual functions in patients. We review this field's history, models of current flow paths in the eye and brain, neurophysiological principles (e.g. entrainment and after-effects), the effects on vision in normal subjects and the clinical impact on plasticity and vision restoration in patients with low vision, with a particular focus on "off-line" or "after-effects". With regard to the therapeutic possibilities, ACS was demonstrated to be effective in patients affected by glaucoma and optic neuropathy, while tDCS and random noise stimulation (tRNS) are most promising for the treatment of amblyopia, hemianopia and myopia. In addition, rTMS applied above the occipital area is a promising approach to treat migraine, neglect and hemianopia. Although the response to these treatment options is better than to sham stimulation in double blinded clinical studies, the clinical efficacy is still rather variable and a proportion of patients do not respond. It is therefore imperative to better understand the mechanisms of action to be able to optimize treatment protocols possibly through personalization of brain stimulation protocols. By identifying the current opportunities and challenges in the field, we hope to provide insights to help improve neuromodulation protocols to restore visual function in patients with visual system damage.

中文翻译：

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使用非侵入性脑刺激进行视力调节、可塑性和恢复——综述

视觉系统是所有感觉系统中最复杂的结构之一，也许是日常生活中最重要的感觉。几十年来，人们对它的功能组织在动物和人类中进行了广泛的研究，例如通过将患者的局限性解剖病变与由此产生的视觉功能障碍相关联。在过去的二十年中，使用非侵入性刺激技术对正常和受损的人眼和大脑进行表征和调节视觉信息处理方面取得了重大成就。技术包括经颅磁刺激 (TMS) 和低强度电刺激，使用直接或交流电 (tDCS 或 tACS) 在视觉皮层附近或上方施加，或经眶施加交流电 (trACS)。在视觉系统经眼眶刺激的情况下，电极连接在眼睛附近、眼睑（经睑电刺激 - TPES）或角膜（tanscorneal 电刺激 TcES）。在这里，我们总结了最先进的视觉系统磁和电刺激作为调节正常视力、诱导大脑可塑性和恢复患者视觉功能的方法。我们回顾了该领域的历史、眼睛和大脑中电流路径的模型、神经生理学原理（例如夹带和后遗症）、对正常受试者视力的影响以及对低视力患者可塑性和视力恢复的临床影响，特别关注“离线”或“后遗症”。关于治疗的可能性，ACS 被证明对青光眼和视神经病变患者有效，而 tDCS 和随机噪声刺激 (tRNS) 最有希望用于治疗弱视、偏盲和近视。此外，在枕部上方应用 rTMS 是治疗偏头痛、忽视和偏盲的一种很有前景的方法。尽管在双盲临床研究中对这些治疗方案的反应比对假刺激更好，但临床疗效仍然存在很大差异，一部分患者没有反应。因此，必须更好地了解作用机制，以便能够通过个性化脑刺激方案来优化治疗方案。通过识别该领域当前的机遇和挑战，