A redout occurs when the body experiences a negative
g-force
The gravitational force equivalent, or, more commonly, g-force, is a measurement of the type of force per unit mass – typically acceleration – that causes a perception of weight, with a g-force of 1 g (not gram in mass measure ...
sufficient to cause a blood flow from the lower parts of the body to the head. It is the inverse effect of a
greyout
A greyout is a transient loss of vision characterized by a perceived dimming of light and color, sometimes accompanied by a loss of peripheral vision. It is a precursor to fainting or a blackout and is caused by hypoxia (low brain oxygen level), ...
, where blood flows away from the head to the lower parts of the body. Usually, a redout will only ever be experienced by pilots, as planes are the most common devices that allow such negative g-forces to be exerted. Redouts are potentially dangerous and can cause
retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
l damage and hemorrhagic
stroke
A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
.
According to the predominant theory, the redness appearing in the visual field is not caused by an actual blood flow to the eye, but it is most likely caused by the blood-laden lower eyelid coming into the visual field because of the pull of negative-Gs.
See also
*
Greyout
A greyout is a transient loss of vision characterized by a perceived dimming of light and color, sometimes accompanied by a loss of peripheral vision. It is a precursor to fainting or a blackout and is caused by hypoxia (low brain oxygen level), ...
*
Fainting
Syncope, commonly known as fainting, or passing out, is a loss of consciousness and muscle strength characterized by a fast onset, short duration, and spontaneous recovery. It is caused by a decrease in blood flow to the brain, typically from ...
*
Presyncope
Lightheadedness is a common and typically unpleasant sensation of dizziness or a feeling that one may faint. The sensation of lightheadedness can be short-lived, prolonged, or, rarely, recurring. In addition to dizziness, the individual may feel ...
References
Visual system
Eye
{{Symptom-stub