Winter Jessica O, Cogan Stuart F, Rizzo Joseph F
Center for Innovative Visual Rehabilitation, VA Medical Center, Boston, MA, USA.
J Biomater Sci Polym Ed. 2007;18(8):1031-55. doi: 10.1163/156856207781494403.
Blindness from retinal diseases, including age-related macular degeneration (AMD) and retinitis pigmentosa (RP), usually causes a significant decline in quality of life for affected patients. Currently there is no cure for these conditions. However, over the last decade, several groups have been developing retinal prostheses which hopefully will provide some degree of improved visual function to these patients. Several such devices are now in clinical trials. Unfortunately, the possibility of electrode or tissue damage limits excitation schemes to those that may be employed with electrodes that have relatively low charge densities. Further, the excitation thresholds that have been required to achieve vision to date, in general, are relatively high. This may result in part from poor apposition between neurons and the stimulating electrodes and is confounded by the effects of the photoreceptor loss, which initiates other pathology in the surviving retinal tissue. The combination of these and other factors imposes a restriction on the pixel density that can be used for devices that actively deliver electrical stimulation to the retina. The resultant use of devices with relatively low pixel densities presumably will limit the degree of visual resolution that can be obtained with these devices. Further increases in pixel density, and therefore increased visual acuity, will necessitate either improved electrode-tissue biocompatibility or lower stimulation thresholds. To meet this challenge, innovations in materials and devices have been proposed. Here, we review the types of retinal prostheses investigated, the extent of their current biocompatibility and future improvements designed to surmount these limitations.
包括年龄相关性黄斑变性（AMD）和视网膜色素变性（RP）在内的视网膜疾病导致的失明，通常会使受影响患者的生活质量大幅下降。目前这些病症无法治愈。然而，在过去十年中，几个研究小组一直在研发视网膜假体，有望为这些患者提供一定程度的视觉功能改善。目前有几种此类设备正在进行临床试验。不幸的是，电极或组织损伤的可能性将激发方案限制在可用于电荷密度相对较低的电极的方案上。此外，迄今为止实现视觉所需的激发阈值通常相对较高。这可能部分是由于神经元与刺激电极之间贴合不佳所致，并且受光感受器丧失的影响而更加复杂，光感受器丧失会在存活的视网膜组织中引发其他病理变化。这些因素以及其他因素的综合作用对可用于向视网膜主动输送电刺激的设备的像素密度施加了限制。使用像素密度相对较低的设备可能会限制通过这些设备可获得的视觉分辨率程度。像素密度的进一步提高以及因此而来的视力提高，将需要改善电极与组织的生物相容性或降低刺激阈值。为应对这一挑战，人们提出了材料和设备方面的创新。在此，我们综述了所研究的视网膜假体类型、其当前的生物相容性程度以及为克服这些限制而设计的未来改进措施。
