Diedrich Erich, Schaeffel Frank
Section of Neurobiology of the Eye, Institute for Ophthalmic Research, Tuebingen, Germany.
Vis Neurosci. 2009 Nov;26(5-6):467-76. doi: 10.1017/S0952523809990253. Epub 2009 Dec 4.
The chicken has been extensively studied as an animal model for myopia because its eye growth is tightly controlled by visual experience. It has been found that the retina controls the axial eye growth rates depending on the amount and the sign of defocus imposed in the projected image. Glucagonergic amacrine cells were discovered that appear to encode for the sign of imposed defocus. It is not clear whether the downstream neurons, the retinal ganglion cells, still have access to this information-and whether it ultimately reaches the brain. We have analyzed the spike rates of chicken retinal ganglion cells in vitro using a microelectrode array. For this purpose, we initially defined spatial resolution and contrast sensitivity in vitro. Two classes of chicken retinal ganglions were found, depending on the linearity of their responses with increasing contrast. Responses generally declined with increasing defocus of the visual stimulus. These responses were well predicted by the modulation transfer function for a diffraction-limited defocused optical system, the first Bessel function. Thus, the studied retinal ganglion cells did not distinguish between a loss of contrast at a given spatial frequency due to reduced contrast of the stimulus pattern or because the pattern was presented out of focus. Furthermore, there was no indication that the retinal ganglion cells responded differently to defocus of either sign, at least for the cells that were recorded in this study.
鸡作为近视动物模型已得到广泛研究，因为其眼睛生长受视觉经验严格控制。研究发现，视网膜根据投射图像中散焦的量和符号来控制眼轴生长速率。人们发现了胰高血糖素能无长突细胞，它们似乎对施加的散焦符号进行编码。目前尚不清楚下游神经元——视网膜神经节细胞——是否仍能获取此信息，以及该信息最终是否能到达大脑。我们使用微电极阵列在体外分析了鸡视网膜神经节细胞的放电率。为此，我们首先在体外定义了空间分辨率和对比度敏感度。根据其对对比度增加的反应线性，发现了两类鸡视网膜神经节细胞。随着视觉刺激散焦增加，反应通常会下降。这些反应能很好地由衍射极限散焦光学系统的调制传递函数（第一类贝塞尔函数）预测。因此，所研究的视网膜神经节细胞无法区分给定空间频率下对比度的降低是由于刺激模式对比度降低还是因为模式呈现为散焦状态。此外，至少对于本研究中记录的细胞，没有迹象表明视网膜神经节细胞对任何一种符号的散焦反应不同。
