'Redout' is caused by excessive -Gz and can occur during manoeuvres such as outside loops. When you Redout you lose your vision and can only see red. Some Medical Books state that redout is due to excess blood rushing to your head and eyes, while Neil Williams believes it is due to your lower eyelid being pulled up to cover your eyes by the negative G loading . Excessive negative G also causes discomfort of the face and eyes as they become engorged by blood and body fluid forced into the head by the G.
