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Temporary blindness, also known as fleeting blindness, is a loss of vision that lasts for only a finite period of time. It can be linked to many causes, from bright flashes of light to more serious medical conditions, such as increased pressure on the brain or optic nerves. People often find temporary blindness to be disconcerting, and it can be problematic if its onset is sudden. People who are driving or engaging in other activities requiring vision can place themselves and others in a great deal of danger if their vision is suddenly impaired.
Flash blindness, or blindness caused by a bright and sudden flash of light, is among the most common forms of temporary blindness. Most people experience it to varying degrees at some point in their lives. The flash of a camera or the transition from a dark room to the bright outdoors can often lead to flash blindness. It is caused when pigments in the retina, which are responsible for perceiving light, become over saturated or bleached. Flashes tend to lead to particularly severe flash blindness at night when the pupils are dilated, allowing a great deal of light into the retinas.
There are many internal conditions unrelated to light that also can lead to temporary blindness. Some conditions cause a buildup of fluids in the brain; this can lead to pressure that affects nerves and cavities that are essential to vision. Blindness persists until such fluids are removed. In some individuals, migraines can also lead to this symptom.
Psychological factors can, in rare cases, cause one to lose vision for a period of time. This tends to occur during times of severe emotional stress. This phenomenon is known as conversion—the brain converts a psychological issue into a physical form.
Some problems of the heart and cardiovascular system can lead to temporary blindness. One such condition is aortic dissection, in which a tear in the wall of the aorta causes blood to flow into the aorta's wall. This changes some properties of the blood that flows to the rest of the body and the brain. As a result, the wrong amount of oxygen reaches the parts of the brain that control vision, so vision is lost.
There are some devices that, for purposes of defense or attack, are used to deliberately induce temporary blindness. There are some explosives used by military and police forces that are specifically designed to create brilliant flashes of light to blind enemies. Some individuals carry sprays such as pepper spray that, when applied to the eyes of an attacker, induce blindness.