Monday, February 6, 2017

Prisms May Be the Light at the End of "Tunnel Vision"

Research Solutions for Peripheral Field Loss (PFL) of Vision


Prisms are a fascinating scientific invention with almost magical properties which most people find amazing.


Because an optical prism, made of transparent glass or plastic, refracts light rays resulting in dispersion of its component colors into that gorgeous "ROY G BIV" (Red-Orange-Yellow-Green-Blue-Indigo-Violet) spectrum which we call a rainbow.

Prism Rainbow

However, as with most technological tools, there are many applications for prisms. In corrective lenses, a prism displaces images off axis, causing the image to be moved in such a way so as to allow it to be seen by those with certain vision impairments.

For example, prism lenses can correct some instances when a person has a misalignment of their two eyes relative to each other that results in binocular diplopia ("double vision"), also called "crossed eyes" or "cross-eyed."

In recent low-vision research news, it was reported that scientists designed new prism-based eyewear to help patients suffering from peripheral vision loss ("tunnel vision") avoid collisions with other pedestrians.

Some medical conditions which cause Peripheral Field Loss (PFL) of vision still retain good central visual acuity. On other words, they can still see what's in the center of their field of vision. Prism-based eyewear can serve as a "visual field expansion device" by creating artificial peripheral islands of vision at an angle making them visible to the unaffected central field of vision of the eye.

(Plain English Translation: Prism eyeglasses can redirect previously unseen peripheral images to the center of vision where they can be seen.)

Tunnel Vision

In a number of cases, optic nerve damage from glaucoma may cause someone to lose their peripheral vision. However, because there are so many other diseases and accidents that can result in tunnel vision, a comprehensive eye exam by a qualified eye doctor is absolutely necessary.

Among the risks associated with peripheral vision loss are pedestrian collisions while walking. The new prism-based eyeglasses are meant to eliminate the risk of collision with other people in crowded locations such as malls, bus terminals or city streets. The study, "The risk of pedestrian collisions with peripheral visual field loss," was published in the Journal of Vision involving 42 retinitis pigmentosa patients with low vision.

Eye Examination

Vision researchers set out to find out which direction these collisions usually occur, which led them to discover that collisions typically occur at a 45-degree angle. The study’s lead author, Eli Peli, OD, professor of ophthalmology with the Schepens Eye Research Institute, at the Massachusetts Eye and Ear, Harvard Medical School, said, "This means that any visual-field expanding device will be most effective if it can cover that angle."

Unfortunately, at present, commercial prisms are limited to 30-degrees. The research scientists made prototypes of high-power prism eyewear closer to the desired 45-degree mark to utilize the viewer's sighted area.

Patients who will require these glasses to expand peripheral vision, including those with retinitis pigmentosa (RP), Usher syndrome, choroideremia, advanced glaucoma, hemianopia, and similar diseases affecting eyesight, usually have good central vision.

The vision scientists, who conducted this study, used prism-based eyewear they developed, based on a mathematical model they created, that determined the risk of collision for those they studied. Experimentally, this new eyeglass design manipulated light to hit areas of the eye that still provide sight, thereby helping those experiencing peripheral visual field loss avoid collisions with other people while walking.

MaxiAids has been serving those with low vision and the blind, as well as seniors, the deaf, the hard of hearing, and the disabled for the past 30 years as a leader in providing assistive devices for independent living. Browse our Low Vision Store.


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