Snow blindness – what are the symptoms and how can you combat it?

Be it during Alpine tours over glaciers, on snowshoe hikes, winter walks or ski tours, or even when sailing or kayaking: you can suffer from snow blindness all year round. Most of the time, your eyes will recover on their own, but it’s still worth using the right sun protection if you want to avoid any long-term consequences. But how can I reliably protect my eyes from the sun? What should I look out for when buying glasses and what should I do if I experience symptoms of snow blindness?

What is snow blindness and how does it occur?

Snow blindness, technically known as photokeratitis, causes inflammation of the eye’s connective tissue and the cornea. This is triggered by UV radiation from the sun, which reaches the eye either directly or indirectly. In other words, snow blindness is akin to having a sunburn on your eye.

UV radiation rarely reaches the eye directly: for this to occur, you’d have to stare at the sun, which quickly becomes unpleasant. Snow blindness is primarily caused by the reflection of the rays on light-coloured surfaces such as ice, snow or even sand, stone and water, which means they hit your eyes in weakened form.

It’s important to know that clouds, fog or snowfall do not filter the sun’s UV radiation out of the air, so you can even end up suffering from snow blindness on a cloudy, gloomy day.

What are the symptoms of snow blindness?

Snow blindness manifests itself in many different ways, which change depending on the severity of the condition.

• At first, you usually notice that your surroundings are becoming more and more dazzling. In other words, you become more sensitive to light. Often, the body reacts automatically by making you squint, and your eyes might also start to water and/or burn.

• After a few hours (about 6 to 12 hours), this is joined by additional symptoms, such as poor vision, red eyes, a feeling of there being a foreign object in the eye, and swelling of the eyelids and small blood vessels.

It’s perfectly possible that you might only feel like you’re being dazzled during your ski tour or kayaking session and won’t notice any other symptoms. In the evening, though, your eyes could start to tear up, burn and feel like you have sand in them. This foreign body sensation is due to the fact that the outermost layer of the cornea is so severely damaged that it detaches itself. As a result, nerve endings are exposed, leaving your eyes extremely sensitive.

How can you prevent snow blindness?

Good sunglasses are the best protection against snow blindness, as they block the UV radiation. Conventional sunglasses simply aren’t enough, though, especially in snowy mountains environments, when skiing or when on glacier tours. In these cases, the rays come to you from almost every angle – reflected from snowy slopes, from ice and snow on the ground and directly from the sun. That’s why it’s important that the glasses cover as much of your field of vision as possible – so wear ski goggles or glacier goggles.

It’s important that the glasses are of good quality. Although darkened lenses generally reduce glare, it’s impossible to tell from the tint alone whether the UV filter is strong enough or even present at all. All glasses sold in Switzerland must bear a CE mark, which guarantees that the lenses have UV protection. Sunglasses are also divided into different categories. You can find more information here.

What categories of sunglasses are there?

According to the international standard ISO 12312–1:2022, sunglasses are divided into five categories. When buying sunglasses, look for the CE mark and a reference to the ISO standard on the label. There are five categories:

• Category 0: not suitable for use as sunglasses, lets through over 80% of light

• Category 1: not suitable for use as sunglasses, protects slightly against UV radiation and glare, but lets through up to 80% of light

• Category 2: suitable for use as everyday sunglasses, provides good protection against glare and UV radiation, lets through up to 43% of light

• Category 3: suitable for everyday use and for places with a lot of sun (e.g. mountains, beach), very good protection against glare, lets through up to 18% of light

• Category 4: special glasses for extreme conditions, for example on the water (kayaking), in the desert, in the high mountains or in the snow. Very high glare protection, including on the side. Remember that these lenses are not approved for use when driving because they are so dark that you can’t clearly recognise traffic lights. The side glare protection additionally restricts your field of vision, which can also be dangerous on the road.

Regardless of the category, the UV protection effect is only guaranteed for two years. Scratches – and time – reduce the level of protection.

What should you do in the event of snow blindness?

Shade: your eyes need a break. Stay in a dark room and protect your eyes from further sunlight. Wear sunglasses indoors, too. While it might get boring after a few hours, giving your eyes a break also means putting your smartphone away and not watching TV or reading, either on paper or on an e-reader.

Coolness: take compresses, cotton pads or small pieces of fabric, wet them and place them on your closed eyes. This has a cooling and calming effect. You can also put the compresses in the fridge briefly, but don’t let them get too cold, as this would further irritate your eyes.

Moisture: eye drops keep the eyes moist and also have a temporary cooling effect. Eye ointments can also help, as they usually last a little longer.

Rest: don’t rub your eyes, as this can worsen the symptoms.

In most cases, the symptoms completely dissipate within 24 to 48 hours if the eyes are treated with care. If the symptoms persist for longer than this, be sure to consult a medical professional – if possible, an ophthalmologist. If left untreated, severe snow blindness can have long-term consequences for your vision.

What are the risk factors for snow blindness?

The greatest risk factor for snow blindness is not wearing sunglasses. However, there are other aspects to consider:

• UV radiation is higher in the mountains than at lower altitudes. Exposure increases by around 10% per thousand metres in altitude.

• Fresh snow reflects the light the most: it’s not yet been covered by dust, sand or leaves, which means it’s particularly white.

• Contact lenses dry out the eyes. Dry eyes are more prone to snow blindness, and the risk of a more unpleasant and prolonged experience is increased.

• Some medications, such as antibiotics, can make people sensitive to light. If possible, plan your adventure for a time when you don’t need to take medication or have the risk level assessed by a doctor in advance.

Tips for combating snow blindness

Watch out for your friends: is someone squinting? Or did someone even forget their sunglasses? Do you have any spare pairs? Otherwise, depending on the conditions, you should call off your trip before you even set off, find a pair of sunglasses or make your way back.

Pack spare sunglasses: be prepared in case your actual sunglasses get broken or lost, or someone else needs a replacement pair. This is particularly useful for multi-day activities, such as treks, extensive snowshoe hikes, or ski or glacier tours.

Don’t look directly at the sun: even if you have a good pair of glasses and aren’t being dazzled by it.

Spend your lunch break in the shade or take additional steps to protect yourself: because UV exposure is at its highest at midday, you should also wear a wide-brimmed hat, for example.

Take into account the amount of light around you: UV radiation often also hits the sides of your eyes. Wide glasses frames or glare protection shield them, while a hat protects against direct radiation from above.

Keep your sunglasses to hand: once they’re stowed in your backpack, you won’t be able to get them out all that quickly.

Polarised sunglasses: in addition to the UV filter, these lenses have a special coating which further reduces glare. Polarised sunglasses provide better visibility, but cannot prevent snow blindness in general.

Children have more sensitive eyes than adults, but react less strongly to glare: this makes them particularly susceptible to snow blindness, so it’s crucial to ensure that children also have good sun protection.