A normal visual field of each eye extends to approximately 80 degrees nasally (to the nose) and 90 degrees temporarily (to the ear). With both eyes together a normally sighted individual can see an almost 180 degree field of view. (To understand what a degree is, extend your arm fully at shoulder height and bend your hand upward to the ceiling at the wrist—the width of your hand is approximately 10 degrees in diameter.) The peripheral retina is most sensitive to motion and sees best in low light (scotopic vision). It does not have the resolving power (highest visual acuity) of the macula (which is designed to provide our sharp, detail vision and works most well in bright light [photopic vision]).
Individuals with tunnel vision from disorders such as Retinitis Pigmentosa, Choroideremia, Glaucoma and strokes of the optic nerve (Ischemic Optic Neuropathy) will note that they see more poorly at night and tend to bump into objects (for example door jams and low hanging branches) in their side vision. Tunnel vision usually develops slowly and individuals can learn to scan more to help them walk and move safely. When fields of view become very narrow (perhaps 10 degrees diameter or less) sighted guides, long canes, and guide dogs become very helpful.
Optical devices that minify the image (like hotel room peep holes), sometimes called reversed telescopes, may also be of value. These make the image smaller allowing more to be seen in the same amount of space. Ocutech makes three versions of optical minification devices—the Image Minifier, Field Viewer, and the Field Expander. As compared to reversed telescopes that produce barrel distortion and an unnatural image, Ocutech minification systems are designed to provide a sharp, flat image that is more natural, and easier to use.
Visit our Minification Devices for Tunnel Vision product page.
Watch our video demonstration about Image Minification for Tunnel Vision.