Goetz Georges, Smith Richard, Lei Xin, Galambos Ludwig, Kamins Theodore, Mathieson Keith, Sher Alexander, Palanker Daniel
Hansen Experimental Physics Laboratory, Stanford University, Stanford, California, United States 2Department of Electrical Engineering, Stanford University, Stanford, California, United States.
Santa Cruz Institute for Particle Physics, University of California Santa Cruz, Santa Cruz, California, United States.
Invest Ophthalmol Vis Sci. 2015 Nov;56(12):7186-94. doi: 10.1167/iovs.15-17566.
To evaluate the contrast sensitivity of a degenerate retina stimulated by a photovoltaic subretinal prosthesis, and assess the impact of low contrast sensitivity on transmission of visual information.
We measure ex vivo the full-field contrast sensitivity of healthy rat retina stimulated with white light, and the contrast sensitivity of degenerate rat retina stimulated with a subretinal prosthesis at frequencies exceeding flicker fusion (>20 Hz). Effects of eye movements on retinal ganglion cell (RGC) activity are simulated using a linear-nonlinear model of the retina.
Retinal ganglion cells adapt to high frequency stimulation of constant intensity, and respond transiently to changes in illumination of the implant, exhibiting responses to ON-sets, OFF-sets, and both ON- and OFF-sets of light. The percentage of cells with an OFF response decreases with progression of the degeneration, indicating that OFF responses are likely mediated by photoreceptors. Prosthetic vision exhibits reduced contrast sensitivity and dynamic range, with 65% contrast changes required to elicit responses, as compared to the 3% (OFF) to 7% (ON) changes with visible light. The maximum number of action potentials elicited with prosthetic stimulation is at most half of its natural counterpart for the ON pathway. Our model predicts that for most visual scenes, contrast sensitivity of prosthetic vision is insufficient for triggering RGC activity by fixational eye movements.
Contrast sensitivity of prosthetic vision is 10 times lower than normal, and dynamic range is two times below natural. Low contrast sensitivity and lack of OFF responses hamper delivery of visual information via a subretinal prosthesis.
评估光伏视网膜下假体刺激退化视网膜时的对比敏感度，并评估低对比敏感度对视觉信息传递的影响。
我们在离体条件下测量了白光刺激健康大鼠视网膜的全视野对比敏感度，以及视网膜下假体在超过闪烁融合频率（>20Hz）时刺激退化大鼠视网膜的对比敏感度。使用视网膜的线性-非线性模型模拟眼球运动对视网膜神经节细胞（RGC）活动的影响。
视网膜神经节细胞适应恒定强度的高频刺激，并对植入物光照的变化产生短暂反应，表现出对光的开、关以及开和关的反应。随着退化的进展，具有关闭反应的细胞百分比降低，表明关闭反应可能由光感受器介导。假体视觉的对比敏感度和动态范围降低，引发反应需要65%的对比度变化，而可见光引发反应的对比度变化为3%（关闭）至7%（开启）。假体刺激引发的最大动作电位数量最多为自然状态下开启通路对应数量的一半。我们的模型预测，对于大多数视觉场景，假体视觉的对比敏感度不足以通过注视性眼球运动触发RGC活动。
假体视觉的对比敏感度比正常情况低10倍，动态范围比自然状态低两倍。低对比敏感度和缺乏关闭反应阻碍了通过视网膜下假体传递视觉信息。
