Tunnel vision is the loss of peripheral vision with retention of central vision, resulting in a constricted circular tunnel-like field of vision.^*

Tunnel vision can be caused by:

• Retinitis pigmentosa, a disease of the eye.
• Sustained (1 second or more) high accelerations ^*. Typically, flying a 'plane 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.
• Glaucoma, a disease of the eye.
• Extreme fear or distress, most often in the context of a panic attack.
• Altitude sickness, hypoxia in passenger aircraft ^*
• Exposure to oxygen at a partial pressure above 1.5-2 atmospheres, producing central nervous system oxygen toxicity, notably while diving. ^* 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 ^*.
• Pituitary stalk mass (i.e. tumor) compressing optic nerve fibers

When combined with piloting an aircraft, driving, crossing roads or operating heavy machinery, the consequences have been known to be fatal.

Vision

Tunnel vision is a metaphor for narrowmindedness, particularly in describing those who pursue an investigation with their conclusion already decided and proceed by only accepting evidence that supports their conclusion and excluding any evidence that contradicts their assumptions.

Tunnel vision is also a (positive) metaphor for the largely intuitive ability to focus only on what is crucial and relevant to solving a problem. To put this another way, it's the ability to ignore a distracting lack of knowledge while learning just enough to solve a problem.

The term is widely used this way in the software industry.