Snow Blindness

Snow blindness (formally referred to as photokeratitis) is sunburn of the eyes caused by the sun's UV rays. It becomes more of a problem at higher altitudes and in polar regions, though it doesn't require snow. At higher elevation, the sun's rays are stronger, and fresh snow reflects about 80% of the sun's radiation. Snow blindness is extremely painful but easily preventable. For this reason, it is important to wear proper eye protection when hiking. Below I cover the symptoms, the treatment, and the prevention options, from proper gear down to a field-made fix.

Why snow blindness happens at altitude and on snow

Your skin is not the only part of you that burns. The surface of the eye, mainly the clear front layer called the cornea, can be damaged by ultraviolet light in much the same way a shoulder can. Photokeratitis is simply the medical name for that burn.

Two things stack the odds against you in the mountains. The first is elevation. The higher you climb, the less atmosphere there is to filter the sun, so the rays reaching you are stronger. The second is the ground itself. Fresh snow reflects about 80% of the sun's radiation, which means you are hit from above and again from below, and a hat brim does very little about the light bouncing up at you.

That is also why snow blindness is not strictly a snow problem. Bright, open terrain at high elevation can do it, and so can any wide, light-coloured surface under a strong sun. Cloud cover is no guarantee either, because UV can still get through a thin or broken overcast. Plenty of people only discover this at the end of a hazy day when their eyes start to feel gritty.

Symptoms of snow blindness

Symptoms of snow blindness may include extreme eye pain, inability to keep eyes open, tearing, and bloodshot eyes. Many people describe the feeling as sand or grit under the lids, and bright light of any kind becomes hard to bear. Snow blindness may result in temporary loss of vision. In extreme cases, repeated exposure may result in permanent loss of vision.

It helps to know the terminology. You may see the condition called photokeratitis, UV keratitis or, in older writing, "arc eye" or "welder's flash", since welding arcs produce the same kind of damage. They are the same basic injury with different causes.

The pain can be severe enough that a person cannot easily walk, read a map or look after themselves. On a trip that matters, because a hiker who cannot open their eyes is dependent on the rest of the group. That is one more reason to treat eye protection as core kit rather than an optional extra.

Why the pain arrives late

These symptoms, like sunburns, usually appear several hours later or the day after. That delay is the trap. You can spend a whole day on a bright snowfield feeling perfectly fine, take your eye protection off at camp, and only start to hurt that night or the next morning, by which point the damage is already done.

The delay also means you cannot use comfort as your guide. If your eyes feel fine at noon, that tells you nothing about whether they are being harmed. Squinting is a warning sign worth taking seriously, and so is watering eyes in bright conditions. If you are squinting for most of the day without eye protection, you are already taking in more light than you should.

A common mistake is swapping to lighter lenses or taking glasses off during a cloudy stretch, then getting caught as the sun breaks through. My advice, and I will stand by it, is to keep the protection on for the entire time you are on snow or high, exposed ground, even when the day looks dull.

Prevention: choosing the right sunglasses

Preventing snow blindness is as simple as wearing proper eye protection. There are several options available, and the right one depends on the conditions.

Sunglasses: Sunglasses are an option and can be worn for everyday activities. The best sunglasses to prevent snow blindness are sunglasses that offer full-coverage. These sunglasses "wrap around" and also prevent rays from entering the sides. Polarized or dark mirror-coated sunglasses that offer 100% UV protection work the best.

Two points are worth checking before you buy. First, look for a clear statement of UV protection on the label rather than judging by how dark the lens looks. A dark lens without UV filtering can actually make things worse, because your pupils open wider behind it and let in more of the rays it fails to block. Second, check the fit. Light leaking in around the frame from the side, top or bottom defeats the purpose, which is why wraparound shapes and side shields matter on snow.

For activities involving winter sports and snowfields, consider glacier sunglasses or glacier goggles. These sunglasses are specifically designed for protection in the outdoors.

Snow goggles for wind and blizzard conditions

Snow goggles: If you are in windy or blizzard conditions, snow or ski goggles with UV protection will work best. Another advantage to wearing snow goggles is that they work better with a face mask and offer protection against frostbite.

Goggles earn their place when wind, spindrift or falling snow is in play. They seal around the eye area, so nothing blows in behind the lens, and they keep wind off the delicate skin around the eyes. Open-frame sunglasses simply cannot do that. They also sit more comfortably over a buff or face mask than sunglasses do, which tend to fog when exhaled air is pushed up from underneath.

The same rule applies as with sunglasses: the lens needs a UV rating, and a tint suited to bright conditions. A pair of clear or low-light goggles is the wrong tool for a sunny snowfield. Many people carry both a pair of sunglasses for fair weather and goggles for storms, which is sensible, since conditions can flip within an hour. If your trip is a longer cold-weather outing, the broader gear advice in our guide to winter hiking and camping fits well alongside this.

Improvising eye protection in the field

Other options: It's possible you may find yourself in a harsh environment without eye protection. If this happens, you can improvise by making Eskimo sunglasses. These are makeshift sunglasses that are made from birch bark, cardboard, or other such material. Shape the material to a pair of sunglasses and cut slits in the eyes. You can rub charcoal on the inside of the slits to prevent reflection. Next, tie the sunglasses around your head using a piece of string.

The principle is worth understanding because it applies to any improvised fix. You are cutting the amount of light that gets to the eye, and a narrow slit does that very effectively. Blackening the inside stops light bouncing around within the material and into your eye. Anything stiff, opaque and easy to cut will do the job in a pinch.

I would not call this a substitute for the real thing. It limits your field of view, which matters on uneven or icy ground, so move slowly and watch your footing. Think of it as a get-you-down-the-mountain measure. Packing a spare pair of sunglasses is far easier, and a lost or broken pair is a common way people end up needing the improvised version in the first place.

Treatment of snow blindness

Those with snow blindness will usually recover in 2-3 days without any medical treatment. If you wear contact lenses, you should take them out immediately and wait to wear them again until your eyes have healed and returned back to normal.

Here are a few things you can do to treat snow blindness:

• Stay indoors and avoid sunlight.
• Wear sunglasses
• Keep your eyes moistened with artificial tears
• Cold compress, such as a cool dampened washcloth
• Pain relievers

Each of these has a simple purpose. Staying out of the light gives the cornea a chance to repair without more irritation. Artificial tears keep the surface lubricated, and a cool damp cloth over closed eyes eases the burning. Pain relievers take the edge off the worst of it. Try not to rub your eyes, however tempting that is, since rubbing can irritate an already damaged surface.

Recovering on a trip and knowing when to get help

If it happens on a multi-day trip, the practical side gets harder than the medical side. A person who cannot tolerate light needs shelter, shade and company. Setting up in a spot out of the glare makes a real difference, and so does the choice of campsite in the first place, something we look at in our piece on choosing a winter campsite. A roomy, sturdy shelter helps too, as you will see in our notes on extreme weather tents. Whoever is affected should not be hiking out alone while half blind, so plan the descent as a group.

Because the usual course is recovery in a couple of days, you can treat mild cases at camp or at home. But eye injuries are not something to guess about. If the pain is not easing, if your vision stays blurry, or if you are unsure that it is snow blindness at all, see a medical professional. General eye-safety information is available from public health bodies such as the Centers for Disease Control and Prevention.

It is worth remembering that repeated exposure is the route to lasting harm. One bad day usually heals. A habit of skipping eye protection is what worries me. Seasons also blur at altitude, so even shoulder-season trips can bring bright snow, as our look at when shoulder season becomes winter explains. Pack the sunglasses before the stove, and your eyes will thank you.