Williams T P, Henrich S, Reiser M
Biomedical Research Facility, Florida State University, Tallahassee 32306, USA.
Invest Ophthalmol Vis Sci. 1998 Mar;39(3):603-9.
To determine the effects of eye closure and opening on photostasis, the regulation of light absorption by retinal rods in the albino rat.
The approach was to measure the effect of eye closure and opening on rhodopsin bleaching in situ and to use those results to simulate what happens to rhodopsin when a living rat opens or closes its eyes during daylight exposure. Completely dark-adapted, dead albino rats, each with one eye closed or open, were exposed to a standard lighting situation. The rhodopsin bleaching rate in closed versus open eyes was measured. Rhodopsin bleached at a more reduced rate in closed eyes than in open eyes. This measured reduction of rate in closed eyes was applied to a simulation of rhodopsin bleaching in open and closed eyes. The simulation used idealized conditions to verify the simulation itself, and then it was applied to previously published photostasis results.
Rhodopsin in closed eyes bleaches at half the rate found in open eyes. The absorption spectrum of rat red blood cells was compared with the rate rhodopsin absorption spectrum, and the comparison showed that blood does not absorb the main-band wavelengths of rhodopsin. Simulating rhodopsin bleaching with eyes closed (half intensity) and open (full intensity) during daylight hours showed a slight effect on the total number of photons absorbed in an entire day. The simulation set limits to the maximal effect of eyes open all day versus eyes closed all day. At a habitat intensity of 200 lux, for example this maximal effect (eyes always open versus always closed) was calculated to be +/- 9%. At the lowest intensity, 3 lux, this maximal effect was +/- 28%, but it is only 1% at the highest intensity, 400 lux.
Eye closures and openings have a slight effect on photostasis in albino rats. There are two reasons for this: The eyelids reduce the effective bleaching intensity by half. Moreover, during the "dim-out" of closure, rhodopsin continues to regenerate and approaches a new, higher value. This accumulation of rhodopsin enhances the rate of photon absorption because the rate is proportional to the product (rhodopsin x intensity). Thus, the increased rhodopsin concentration in the rods partially compensates for the reduced intensity of lid closure, and the photon absorption rates, with eyes closed, do not decrease by the full factor of 2 implied by the intensity reduction. In addition, when the eyes are subsequently opened after such a dim-out, the retina is suddenly exposed again to the full intensity of the environment. At this time, photon absorption rate, rhodopsin x intensity, is transiently higher than just before eye opening. Thus, the compensatory interplay between bleaching and regeneration in closed and open eyes results in the near compensation of light absorption and maintenance of the stasis close to 10(16) photons per eye per day.
确定闭眼和睁眼对白化大鼠视网膜杆细胞光稳态（即光吸收调节）的影响。
通过测量闭眼和睁眼对原位视紫红质漂白的影响，并利用这些结果模拟活体大鼠在白天暴露期间睁眼或闭眼时视紫红质的变化情况。将完全暗适应的死亡白化大鼠，每只一只眼闭合或睁开，暴露于标准光照条件下。测量闭合眼与睁眼的视紫红质漂白速率。闭合眼中视紫红质的漂白速率低于睁眼中的漂白速率。将测量得到的闭合眼漂白速率降低值应用于视紫红质在睁眼和闭眼中漂白的模拟。该模拟使用理想化条件来验证模拟本身，然后将其应用于先前发表的光稳态结果。
闭合眼中的视紫红质漂白速率是睁眼中的一半。将大鼠红细胞的吸收光谱与视紫红质吸收光谱进行比较，结果表明血液不吸收视紫红质的主带波长。模拟白天睁眼（全强度）和闭眼（半强度）时视紫红质的漂白情况，结果显示对全天吸收的光子总数有轻微影响。该模拟设定了全天睁眼与全天闭眼的最大影响限度。例如，在栖息地光照强度为200勒克斯时，这种最大影响（始终睁眼与始终闭眼相比）经计算为±9%。在最低强度3勒克斯时，这种最大影响为±28%，但在最高强度400勒克斯时仅为1%。
闭眼和睁眼对白化大鼠的光稳态有轻微影响。原因有两个：眼睑将有效漂白强度降低了一半。此外，在闭眼导致的“渐暗”过程中，视紫红质继续再生并接近一个新的更高值。视紫红质的这种积累提高了光子吸收速率，因为该速率与乘积（视紫红质×强度）成正比。因此，杆细胞中视紫红质浓度的增加部分补偿了闭眼时强度的降低，并且闭眼时的光子吸收速率不会因强度降低而完全降低两倍。此外，在这种渐暗后随后睁眼时，视网膜会突然再次暴露于环境的全强度光照下。此时，光子吸收速率，即视紫红质×强度，会短暂高于睁眼之前。因此，闭眼和睁眼时漂白与再生之间的补偿性相互作用导致光吸收几乎得到补偿，并维持光稳态接近每只眼每天10¹⁶个光子。
