For this, functional aspects come into play: the storage of retinal and the adaption of the reaction speed. Visual cycle: The visual cycle fulfills an essential task of maintaining visual function and needs therefore to be adapted to different visual needs such as vision in darkness or lightness.The normal transepithelial transport of ions would be too slow to compensate quickly enough for these changes, there are many underlying mechanisms based on the activity of voltage-dependent ion channels add to the basic transepithelial transport of ions. Spatial buffering of ions: Changes in the subretinal space are fast and require a capacitative compensation by RPE many cells are involved in transduction of light and if they are not compensated for, they are no longer excitable and proper transduction would not be possible.RPE supply nutrients to photoreceptors, control ion homeostasis and eliminate water and metabolites. This is important for the immune privilege (not only as barrier, but with signalling process as well) of eyes, a highly selective transport of substances for a tightly controlled environment. Epithelial transport: As mentioned above, RPE compose the outer blood–retinal barrier, the epithelia has tight junctions between the lateral surfaces and implies an isolation of the inner retina from the systemic influences.The combination of light and oxygen brings oxidative stress, and RPE has many mechanisms to cope with it. The high perfusion of retina brings a high oxygen tension environment. ![]() Melanosomes absorb the scattered light and thus diminish the photo-oxidative stress. This role is very important for two main reasons, first, to improve the quality of the optical system, second, light is radiation, and it is concentrated by a lens onto the cells of the macula, resulting in a strong concentration of photo-oxidative energy.
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