Greyout

Greyout

Illustration of a greyout experience

A greyout is a temporary condition characterized by a partial loss of vision, often described as a dimming or blurring of vision, without a complete loss of consciousness. It is typically caused by a decrease in blood flow to the brain, which can occur during rapid acceleration or deceleration, such as in high-speed aviation or during certain medical conditions.

Causes

Greyouts are primarily caused by a reduction in blood flow to the brain, which can result from:

• Orthostatic hypotension: A sudden drop in blood pressure when standing up quickly.
• G-force exposure: Experienced by pilots and astronauts during rapid acceleration.
• Dehydration: Leading to reduced blood volume and pressure.
• Hypoglycemia: Low blood sugar levels affecting brain function.
• Hyperventilation: Causing a decrease in carbon dioxide levels and subsequent vasoconstriction.

Symptoms

The symptoms of a greyout can vary but often include:

• A sensation of dimming or blurring of vision.
• A feeling of lightheadedness or dizziness.
• A sense of "tunnel vision," where peripheral vision is lost.
• A feeling of weakness or fatigue.

Prevention and Management

Preventing greyouts involves addressing the underlying causes:

• Hydration: Ensuring adequate fluid intake to maintain blood volume.
• Gradual position changes: To prevent orthostatic hypotension.
• Proper nutrition: To maintain stable blood sugar levels.
• Controlled breathing: To avoid hyperventilation.

In aviation, pilots are trained to recognize the onset of greyouts and take corrective actions, such as adjusting their posture or using anti-G suits to counteract the effects of high G-forces.

Related pages

• Blackout (vision)
• Syncope (medicine)
• G-force
• Orthostatic hypotension