snow blindness

Snow blindness (also known as ultraviolet keratitis, photokeratitis or niphablepsia) is a painful eye condition, caused by exposure of unprotected eyes to the ultraviolet (UV) rays in bright sunlight reflected from snow or ice or less commonly from sea or sand.^[1] Fresh snow reflects about 80% of UV radiation compared to a dry, sandy beach (15%) or sea foam (25%).^[2] This is especially a problem in polar regions and at high altitudes,^[3] as with every thousand feet (approximately 305 meters) of elevation (above sea level), the intensity of UV rays increases by four percent.^[4]

Snow blindness is akin to a sunburn of the cornea and conjunctiva, and may not be noticed for several hours after exposure. Symptoms can run the gamut from eyes being bloodshot and teary to increased pain, feeling gritty and swelling shut. In very severe cases, snow blindness can cause permanent vision loss.

To prevent snow blindness, people who are at risk are recommended to use sunglasses that transmit 5-10% of visible light and absorb almost all UV rays. Additionally, these glasses should have large lenses and side shields to avoid incidental light exposure. Sunglasses should always be worn, even when the sky is overcast as UV rays can pass through clouds.^[5]

If snow blindness does occur, treatment consists of quickly easing the pain with topical anesthetics applied in eye drops and the use of cold wet compresses. Further injury should be avoided by isolation in dark room, removing contact lenses, not rubbing the eyes, and wearing sunglasses until the symptoms disappear completely.^[3] There is also an ointment that significantly speeds up recovery.^[6]

In the event of lost or damaged sunglasses, emergency goggles can be made by cutting slits in dark fabric or tape folded back onto itself. The SAS Survival Guide recommends blackening the skin underneath the eyes with charcoal to avoid any further reflection.^[7]

Inuit

Traditional Inuit goggles used to combat snow blindness

The Inuit carved goggles from caribou antlers to help prevent snow blindness. The goggles were curved to fit the user's face and had a large groove cut in the back to allow for the nose. A long thin slit was cut through the goggles to allow in a small amount of light, diminishing the amount of UV rays that get through. The goggles were held to the head by a cord made of caribou sinew.^[8]

See also

• Albedo
• Glare (vision)
• Over-illumination

• Arc eye, a similar condition sometimes experienced by welders.

References

External links

• An Experience of Snow Blindness
• Historical Snow Goggles