Human Cone Transduction

人眼通过一层特殊的感光细胞和被称为视网膜的神经细胞来探测光线，视网膜位于眼睛的后部。光能用称为量子的单位来描述；光能转化为细胞输出的神经信号称为转导。光感受器内的电反应是由已知最快的化学反应引起的。尽管这些反应速度很快，但这些细胞输出的总响应时间相当慢，最多只有十分之一秒，因为有一连串的生化反应有效地放大了信号能量。视杆细胞和视锥细胞是两种基本的光感受器，它们在视网膜上发出视觉信号，然后由视神经发送到大脑。视锥系统通常用于强日光下的色觉，而视杆系统对弱光非常敏感，但本身不携带颜色信息。本项目研究人眼视锥细胞转导过程的组成机制，利用人的反应来获得看到高度控制的持续时间和强度的刺激光的阈值。将测量锥体系统处于黑暗适应状态时对单次闪光的响应，测量不同类型锥体在绝对阈值处吸收的量子数，以及测量适应黑暗的锥体响应中的不同时间分量。这种新颖的方法将产生重要的关于人类正常视觉的新的基础信息，这将对进一步理解视觉的生物化学和生理学产生影响。

The human eye detects light by a sheet of specialized photoreceptor cells and nerve cells called the retina, at the back of the eye. Light energy is described in terms of units called quanta; the conversion of light energy to a neural signal output by the cell is called transduction. The electrical response within the photoreceptors is initiated by the fastest chemical reactions known. Despite the speed of these reactions, the total response time for the output of these cells is rather slow, to as much as a tenth of a second, because there is a cascade of biochemical reactions that effectively act to amplify the signal energy. Two basic kinds of photoreceptors, called rods and cones, initiate visual signals in the retina which then are sent to the brain by the optic nerve. The cone system is usually used for color vision in strong daylight illumination, while the rod system is very sensitive to low light level but does not carry color information by itself. This project examines the component mechanisms of the cone transduction process in the human eye, using human responses to obtain thresholds for seeing stimulus lights of highly controlled duration and intensity. Measurements will be made of responses to single flashes from the cone system when it is in a state of dark adaptation, of the number of quanta absorbed at the absolute threshold for different cone types, and of the different time components in the dark-adapted cone responses. This novel approach will generate important new fundamental information on normal human vision that will have impact on further understanding the biochemistry and physiology of vision in general.