Department of Physics, Stanford University, Stanford, CA, 94305, USA.
Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, 94305, USA.
Sci Rep. 2018 Feb 16;8(1):3145. doi: 10.1038/s41598-018-21447-1.
Subretinal prostheses are designed to restore sight in patients blinded by retinal degeneration using electrical stimulation of the inner retinal neurons. To relate retinal output to perception, we studied behavioral thresholds in blind rats with photovoltaic subretinal prostheses stimulated by full-field pulsed illumination at 20 Hz, and measured retinal ganglion cell (RGC) responses to similar stimuli ex-vivo. Behaviorally, rats exhibited startling response to changes in brightness, with an average contrast threshold of 12%, which could not be explained by changes in the average RGC spiking rate. However, RGCs exhibited millisecond-scale variations in spike timing, even when the average rate did not change significantly. At 12% temporal contrast, changes in firing patterns of prosthetic response were as significant as with 2.3% contrast steps in visible light stimulation of healthy retinas. This suggests that millisecond-scale changes in spiking patterns define perceptual thresholds of prosthetic vision. Response to the last pulse in the stimulation burst lasted longer than the steady-state response during the burst. This may be interpreted as an excitatory OFF response to prosthetic stimulation, and can explain behavioral response to decrease in illumination. Contrast enhancement of images prior to delivery to subretinal prosthesis can partially compensate for reduced contrast sensitivity of prosthetic vision.
视网膜下假体旨在通过对内视网膜神经元的电刺激来恢复因视网膜变性而失明的患者的视力。为了将视网膜输出与感知相关联，我们使用全视野脉冲照明以 20Hz 刺激光电池视网膜下假体研究了盲鼠的行为阈值，并测量了类似刺激离体的视网膜神经节细胞 (RGC) 反应。在行为上，老鼠对亮度变化表现出惊人的反应，平均对比度阈值为 12%，这不能用平均 RGC 放电率的变化来解释。然而，即使平均速率没有显著变化，RGC 也表现出毫秒级的尖峰时间变化。在 12%的时间对比度下，与健康视网膜可见光刺激的 2.3%对比度步长相比，假体反应的发射模式变化同样显著。这表明尖峰模式的毫秒级变化定义了假体视觉的感知阈值。在刺激爆发中的最后一个脉冲的反应持续时间长于爆发期间的稳态反应。这可以解释为对假体刺激的兴奋性 OFF 反应，并可以解释对光照减少的行为反应。在将图像递送至视网膜下假体之前进行对比度增强可以部分补偿假体视觉对比度灵敏度的降低。
