Thousands of years old. Inuit and Yupik people of Alaska and northern Canada carved snow goggles from ivory, antler, bone and wood, hollowed to fit an individual face and cut with very narrow slits. They are among the oldest surviving eye protection anywhere, and they were made for a specific medical problem: photokeratitis, snow blindness, caused by ultraviolet light reflected off snow and ice burning the surface of the eye.

Two effects, one slit. Narrowing the aperture cuts the light reaching the eye dramatically — a thin slit blocks the great majority of reflected light. It also reduces the size of the blur circle on the retina and increases depth of field, so vision through the slit is sharper than without. The maker gets glare protection and improved acuity from a single design decision, which is unusually elegant for any piece of equipment.

Sooting the inside. Blackening the hollow is not decoration. Any light entering the slit that then reflects off a pale interior surface reaches the eye from the wrong direction and reduces contrast. Modern optical instruments blacken their interiors for precisely the same reason.

What they gave up. Field of view. These goggles restrict vision to a narrow horizontal band, and the wearer scans by moving their head. That is a deliberate trade — on open ice the alternative is being unable to see at all within a day — and it is a good example of a design that is only optimal once you know the environment it was made for.

Not a curiosity. Glacier travellers and mountaineers used slit goggles well into the modern era, and the pinhole-aperture effect is still used in optometry: the pinhole occluder held in front of an eye during a sight test works on exactly the same principle. The object is ancient; the optics are current.

Eyes

Blueprints (1)

Snow Goggles