Belay glasses

Belay glasses are eyeglasses with prismatic lenses that are used by belayers in rock climbing to avoid the neck strain commonly associated with belaying.^[1]

Principle of operation of belay glasses. Light from above is reflected into the observer's eye.^[2]

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.^[3] The prismatic lenses of the belay glasses are arranged so as to bend light from above through total internal reflection 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.

• 

  Belay glasses

• 

  View through the prism

• 

  thumb|Y&Y belay glasses

Reference

1. ↑ "How to Use Belay Glasses". The British Mountaineering Council. Retrieved 23 April 2015.
2. ↑ "How belay specs work". Belay Specs. Retrieved 24 April 2015.
3. ↑ Cupido, Carla. "Belayer's Neck". Climbing. Retrieved 23 April 2015.