From the light to the dark, the sensitivity of the human eye to light gradually increases, reaching a maximum of about 30 minutes, called dark adaptation. Dark adaptation is a reflection of the basic function of the cell, the sensitization function. In the case of nutritional deficiencies and fundus lesions, there is often a change in dark adaptation function. Dark adaptation is one of the important items of eye function examination. concept When we walk into the dark place from a bright place, our eyes will be invisible at once, and it will take a while to slowly adapt and gradually see the dark things. This process is about 30. ~40 minutes, during which the sensitivity of the retina's sensitivity is gradually increasing, that is, dark adaptation, that is, the ability of the retina to adapt to the dark. Cause In the dark, the cone cells in the human eye are not working, and only rod-shaped photoreceptors are at work. In the rod-shaped photoreceptor cells, there is a substance called rhodopsin, which is sensitive to weak light, and it can be gradually synthesized in the dark. According to statistics of ophthalmologists, 60% of rhodopsin can be produced in 5 minutes in the dark. It can be generated in about 30 minutes. Therefore, the longer you stay in a dark place, the higher the sensitivity to low light. However, some people have barrier function of rod-shaped photoreceptor cells. In dark places, rod-shaped pigment cells cannot work normally. No matter how long he stays in the dark, they cannot improve the sensitivity to low light. We take this phenomenon. Call it night blindness. Some night blindness is caused by factors such as vitamin A deficiency, and some are caused by diseases such as primary retinitis pigmentosa. Rod-shaped photoreceptors do not have the ability to recognize the color of an object, so looking at things in the dark is a color. Dark reaction Dark adaptation is a phenomenon in which the retinal adapts to darkness or low light intensity and the visual sensitivity increases, which is the corresponding word for adaptation. The light that suddenly disappeared from the bright spot and could not be seen at the time was gradually seen as the time spent in the dark was prolonged. This is a daily phenomenon. The time course of dark adaptation can be accurately determined by human psychophysical methods. After fully accommodating in advance, the room is turned into a dark room, and the time course of the change of the test light threshold is measured, and the dark adaptation curve can be obtained. 5~10 minutes later It began to drop sharply, which made the curve appear tortuous (Kohlrausch's kink). The threshold drop can last for about 30 minutes, then slow down, reaching an extreme value of about 1 hour. From the beginning to the appearance of the Korlausch twist, it is called the first phase or the first phase adaptation, and then the second phase or the secondary adaptation. Since the first phase is mainly based on cone cell adaptation and the second phase is based on rod cell adaptation, only the first phase can be seen in the central recess of only the cone cells. Since the dark-adapted cone cell sensitivity is only increased by several tens of times, the threshold is about 0.02-0.15 lux, but the rod cell sensitivity can vary from thousands to tens of thousands of times, and the threshold is as low as 0.569×10^-5 lux. Therefore, in the peripheral region of the retina with many rod cells, the dark adaptation ability is good and the sensitivity is also high. For this reason, a weak light is visible in the dark (central view) but not visible, and a central scotoma or a physiological night blind phenomenon occurs. If the line of sight is removed, it can be seen through peripheral vision. Since the maximum wavelength of the visual sensitivity curve of the cone cells and the rod cells is different, the dark adaptation curve varies depending on the wavelength of the test light. If red light is used, the sensitivity of the rod cells is low, and the second phase is invisible; if short-wave light with high sensitivity of rod cells is used, the second phase appears early and the extreme value of the measured threshold is also low. These results measured on humans are very similar to those obtained in other vertebrates using electroretinograms and peak discharges of optic nerve fibers as indicators, indicating that dark adaptation is a phenomenon produced by the retina. As for its mechanism, there has long been a view that the threshold is lowered due to the resynthesis of the rod-like visual pigment, rhodopsin (photochemistry), but according to the results of subsequent studies, the increase in the amount of rhodopsin and the decrease in threshold It is not a completely corresponding relationship, and if the retina is locally irradiated, the threshold of the non-irradiated area is also greatly increased. These facts emphasize the existence of neural dark adaptation, and therefore the adaptation of the omentum is considered to be such a mechanism and The combination of photochemical dark adaptation may be appropriate. 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