People sometimes see "stars" in day time. The reason is sometimes when people physically exert themselves or stand up quickly after sitting or bending over, they see little spots of light moving in front of them. This phenomenon can also occur after a blow to the head and is generally referred to as seeing "stars".
It is caused by a condition known as posterior vitreous detachment (which often also results in blurred vision), whereby the vitreous humor — the jellylike fluid that fills the eyeball — detaches from the optic nerve, an action that the brain perceives as flashes of light.
In most cases, this is only temporary and normal vision is restored in a few seconds, but it is more common in elderly people, whose vitreous humor has degenerated and partially liquefied In some cases, the retina can fully detach and the flashes become permanent.
Low blood pressure can also cause flashes, especially when someone changes position quickly In this case, the flashes are caused by a lack of blood flow to the visual areas of the brain.
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