Retinitis PigmentosaTunnel Vision and Night Vision Disorders
Retinitis Pigmentosa is a disorder of the rods, that reduces night vision and the ability to see to the side (Tunnel Vision). Macular vision can remain near normal for a long period of time so often individuals with Retinitis Pigmentosa can read and walk in bright sunlight. Devices that expand the visual field (Image Minifiers and Field Viewers) can help individuals with “Tunnel Vision” see more to the side, helping with mobility and other activities.
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]).
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.