Belay glasses are

eyeglasses Glasses, also known as eyeglasses or spectacles, are vision eyewear, with lenses (clear or tinted) mounted in a frame that holds them in front of a person's eyes, typically utilizing a bridge over the nose and hinged arms (known as temples or ...

with prismatic lenses that are used by belayers in

rock climbing Rock climbing is a sport in which participants climb up, across, or down natural rock formations. The goal is to reach the summit of a formation or the endpoint of a usually pre-defined route without falling. Rock climbing is a physically and ...

to avoid the neck strain commonly associated with belaying. Belay glasses lens

Belaying involves a person standing on a stable platform below a rock climber controlling the tension and friction of the climber's rope. Since this activity requires craning one's neck to look up at the climber, a common malady named "belayer's neck" can occur. The prismatic lenses of the belay glasses are arranged so as to bend light from above through

total internal reflection Total internal reflection (TIR) is the optical phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflected b ...

into the observer's eye, allowing the belayer to observe the climber while maintaining a comfortable head/neck position. The design based on the eyeglasses frame provides for a split field of vision: * the central field through the lenses, providing a vertical view to the climber; * the peripheral field around the sides of the lenses, allowing the belayer to remain aware of their surroundings. The first belay glasses were invented in 2007 by climber Albi Schneider from Germany. File:Port des lunettes.JPG, Belay glasses File:Vue à travers les lunettes.JPG, View through the prism

References

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