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:
Diseases of the eye (glaucoma, retinitis pigmentosa).
Blood loss (hypovolemia).
Alcohol consumption. 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.
Sustained (1 second or more) high accelerations. Typically, flying an airplane with a centripetal acceleration of up to or over 39 m/s2 (about 4g) with the head towards the center of curvature, common in aerobatic or fighter pilots. In these cases, tunnel vision and greyout may proceed to a g-force induced Loss Of Consciousness (g-LOC).
Hallucinogenic drugs, in particular the dissociatives, or stimulant drugs that release and/or prevent the reuptake of dopamine and norepinephrine, in particular amphetamines.
Extreme fear or distress, most often in the context of a panic attack.
High adrenaline production such as intense physical fights, excitement or extreme pleasure, intense anger…
Altitude sickness, hypoxia in passenger aircraft
Exposure to oxygen at a partial pressure above 1.5-2 atmospheres, producing central nervous system oxygen toxicity, called narcosis. Other symptoms can include dizziness, nausea, blindness, fatigue, anxiety, confusion and lack of coordination.
Pituitary tumours (or other brain tumours that compress the optic chiasm)
Prolonged exposure to air contaminated with heated hydraulic fluids and oils, as can sometimes happen in passenger aircraft.
Severe cataracts, causing a removal of most of the field of vision.
During the aura phase of a migraine.
A bite from a black mamba and other snakes with the same strength venom.
Mercury poisoning (especially methylmercury).
Usher Syndrome, a a rare genetic disease that affects both hearing and vision and sometimes also causes problems with balance.
Binoculars, telescopes, and microscopes can also induce an experience of extreme tunnel vision due to the design of the optical components.