Grey out

Grey out or gray out refers to a transient loss of vision characterized by a perceived dimming of light and color, often accompanied by a loss of peripheral vision. It is a condition that can precede a syncope (fainting) or a blackout (complete loss of vision and consciousness), and is commonly associated with a decrease in blood flow to the brain. Grey out is often experienced by individuals in situations of rapid acceleration, such as pilots experiencing high g-forces, and can also occur due to sudden drops in blood pressure, known as orthostatic hypotension.

Causes

The primary cause of a grey out is a reduction in blood flow to the retina and the visual cortex of the brain. This reduction can be due to several factors:

• Orthostatic Hypotension: A sudden drop in blood pressure upon standing up quickly.
• G-Force-Induced Loss of Consciousness (G-LOC): Experienced by pilots and astronauts when rapid acceleration increases g-forces, causing blood to move away from the brain.
• Vasovagal Syncope: A common cause of fainting, where the body overreacts to certain triggers like the sight of blood or extreme emotional distress, leading to a sudden drop in heart rate and blood pressure.
• Dehydration: Reduced blood volume due to dehydration can also decrease blood flow to the brain and eyes, leading to symptoms of a grey out.

Symptoms

Symptoms of a grey out include:

• Dimming of vision
• Loss of color vision
• Tunnel vision or loss of peripheral vision
• Feeling of lightheadedness or dizziness
• Nausea

Prevention and Treatment

Preventing a grey out involves addressing its underlying causes. Measures include:

• Staying hydrated
• Rising slowly from a sitting or lying position to prevent orthostatic hypotension
• Wearing compression garments in situations where G-LOC might occur, such as during certain aerial maneuvers
• Avoiding known triggers for vasovagal syncope

Treatment typically involves lying down or sitting and lowering the head between the knees to increase blood flow to the brain. In cases where grey outs occur frequently or are of concern, medical evaluation may be necessary to rule out underlying conditions.

See Also

• Syncope
• Blackout
• Orthostatic Hypotension
• Vasovagal Syncope