tunnel vision

Normal vision. Courtesy NIH National Eye Institute.

The same view with tunnel vision from retinitis pigmentosa.

In medical terms, tunnel vision is the loss of peripheral vision with retention of central vision, resulting in a constricted circular tunnel-like field of vision.^[1]

Tunnel vision can be caused by:

• Blood loss (hypovolemia)
• Alcohol consumption causes tunnel vision ^[2]. In addition, the vision becomes blurred or double since eye muscles lose their precision causing them to be unable to focus on the same object.
• Retinitis pigmentosa, a disease of the eye.
• Sustained (1 second or more) high accelerations^[3]. Typically, flying an airplane with a centripetal acceleration of up to or over 39 m/s² (4gs) with the head towards the center of curvature, common in aerobatic or fighter pilots. In these cases tunnel vision and brownout may proceed to or g-force induced Loss Of Consciousness (g-LOC).
• Hallucinogenic drugs, in particular the Dissociatives.
• Glaucoma, a disease of the eye.
• Extreme fear or distress, most often in the context of a panic attack.
• During an intense physical fight.
• Altitude sickness, hypoxia in passenger aircraft^[4]
• Exposure to oxygen at a partial pressure above 1.5-2 atmospheres, producing central nervous system oxygen toxicity, notably while diving.^[5] Other symptoms can include dizziness, nausea, blindness, fatigue, anxiety, confusion and lack of coordination.
• Other loss of blood to the brain.
• Prolonged exposure to air contaminated with heated hydraulic fluids and oils, as can sometimes happen in passenger aircraft^[6].
• Pituitary stalk mass (i.e. tumor) compressing the optic chiasm
• Severe cataracts, causing a removal of most of the field of vision
• During the aura phase of a migraine
• Intense anger, due to the body being rapidly flooded with adrenaline and oxygen
• A bite from a Black Mamba and other snakes with the same strength venom.

When combined with piloting an aircraft, driving, crossing roads or operating heavy machinery, the consequences can be fatal.

Metaphor

As a metaphor, tunnel vision denotes the reluctance of individuals to consider alternatives to their preferred line of thought. This could include physicians treating afflictions, detectives considering crime suspects, or anyone predisposed to a favoured outcome.

References

1. ^ Medical terms
2. ^ Effects of Alcohol on Vision
3. ^ Web Archive: Virtual Naval Hospital
4. ^ Web Archive: Aircraft air quality
5. ^ Web Archive: Virtual Naval Hospital, Oxygen Toxity
6. ^ Web Archive: Aircraf air quality