Tunnel vision

For other uses, see Tunnel vision (disambiguation).

File:Human eyesight two children and ball normal vision.jpg

Normal vision. Courtesy NIH National Eye Institute.

File:Human eyesight two children and ball with retinitis pigmentosa or tunnel vision.png

The same view with tunnel vision from retinitis pigmentosa.

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

Medical / biological causes

Tunnel vision can be caused by:

• Blood loss (hypovolemia)
• Alcohol consumption causes tunnel vision . 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. 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 greyout 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 periods of high adreneline production, such as an intense physical fight.
• 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 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.

Eyeglass users

Eyeglass users experience tunnel vision to varying degrees due to the corrective lens only providing a small area of proper focus, with the rest of the field of view beyond the lenses being unfocused and blurry.

Where a naturally sighted person only needs to move their eyes to see an object far to the side or far down, the eyeglass wearer may need to move their whole skull to point the eyeglasses towards the target object.

The eyeglass frame also blocks the view of the world with a thin opaque boundary separating the lens area from the rest of the field of view. The eyeglass frame is capable of obscuring small objects and details in the peripheral field.

Mask, goggle, and helmet users

File:US Navy 050727-N-0295M-010 Electrician's Mate 2nd Class Shane Portton emerges out of the Navy Diver-Explosive Ordnance Disposal (EOD) dive tank exhibit at the 2005 National Scout Jamboree held at Fort A.P. Hill, Va.jpg Wide-field, wrap-around diving mask.

File:Full face diving mask - ocean reef.JPG Diving mask with narrow field of view.

Activities which require a protective mask, safety goggles, or fully enclosing protective helmet can also result in an experience approximating tunnel vision.

Underwater diving masks using a single flat transparent lens usually have the lens surface several centimeters from the eyes. The lens is typically enclosed with an opaque black rubber sealing shell to keep out water. For this type of mask the peripheral field of the diver is extremely limited. Generally, the peripheral field of a diving mask is improved if the lenses are as close to the eye as possible, or if the lenses are large, multi-window, or is a curved wrap-around design.

Protective helmets such as a welding helmet restrict vision to an extremely small slot or hole, with no peripheral perception at all. This is done out of necessity so that ultraviolet radiation emitted from the welding arc does not damage the welder's eyes due to reflections off of shiny objects in the peripheral field.

Optical instruments

File:Navy binoculars.jpg

Extremely large wide-field binoculars that would be impractical to carry.

Binoculars, telescopes, and microscopes induce an experience of extreme tunnel vision due to the design of the optical components.

A wide field microscope or telescope generally requires much larger diameter and thicker lenses, or complex parabolic mirror assemblies, either of which results in significantly greater cost for construction of the optical device.

Wide-field binoculars are possible, but the far end lenses would have to be several centimeters in diameter to widen the field of view, resulting in a bulky device that is difficult to transport and store.

References

nl:Kokervisus