Temporary blindness, also known as fleeting blindness, is vision loss that lasts for only a finite period of time. Temporary blindness can be related 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 disconcerting, and it can be troublesome if its onset is sudden. People who drive or engage in other activities that require vision can put themselves and others in great danger if their vision is suddenly impaired.
Sudden blindness, or blindness caused by a sudden bright flash of light, is one of the most common forms of temporary blindness. Most people experience it to varying degrees at some point in their lives. A camera flash or the transition from a dark room to a bright outside can often lead to flash blindness. It occurs when the pigments in the retina, which are responsible for perceiving light, become saturated or discolored. The flashes tend to lead to sudden blindness, particularly severe at night when the pupils are dilated, allowing a large amount of light onto the retinas.
There are many internal conditions unrelated to light that can also lead to temporary blindness. Some conditions cause a buildup of fluids in the brain; This can lead to pressure on the nerves and cavities that are essential for vision. Blindness persists until these fluids are removed. In some people, migraines can also cause temporary blindness.
Psychological factors can, in rare cases, cause one to lose vision for a period of time. This tends to occur at times of severe emotional stress. This phenomenon is known as conversion: the brain converts a psychological problem into a physical form.
Some heart and cardiovascular system problems can cause temporary blindness. One such condition is aortic dissection, in which a tear in the wall of the aorta causes blood to flow into the wall of the aorta. 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 defensive or offensive purposes, are used to deliberately induce temporary blindness. There are some explosives used by military and police forces that are specifically designed to create bright flashes of light to blind enemies. Some people carry sprays like pepper spray that, when applied to an attacker's eyes, induce blindness.