Snow Blindness and UV Damage: How Sunlight Harms the Eyes

Imagine a perfect day on the slopes: blue sky, fresh snow, hours of skiing. That evening your eyes begin to sting, water and feel as if they are full of sand. By night you can barely open them in the light. This is snow blindness, known medically as photokeratitis, a painful sunburn of the eye's surface caused by ultraviolet (UV) radiation. It is temporary, but it is a vivid reminder that the eyes are just as vulnerable to the sun as the skin.

UV exposure also has slower, quieter effects. Years of sunlight contribute to cataract, growths on the surface of the eye such as pterygium, and skin cancers of the eyelids. This article explains how UV affects the eyes in the short and long term, who is most at risk, and how simple protection can prevent most of the damage.

What UV does to the eye

Sunlight contains ultraviolet radiation that is invisible to us. UVA has longer wavelengths and penetrates deeper; UVB is more energetic and is the main cause of sunburn. The ozone layer filters out most UVC. In the eye, the cornea absorbs most UVB, while the lens absorbs much of the UVA that passes through. This protects the retina in adults but means these front structures take the brunt of UV damage.

The outermost layer of the cornea, the epithelium, consists of cells that renew constantly. Intense UVB exposure damages these cells, which then die and shed over the following hours, exposing the dense nerve endings beneath. That is why photokeratitis is so painful, and why it starts with a delay rather than during exposure. For more background on the eye's structure, see our eye anatomy guide.

Snow blindness and photokeratitis

Symptoms

Symptoms typically appear between about 6 and 12 hours after exposure, which means many people do not connect them with the sun. They include:

• Pain, burning or a gritty, sandy sensation in both eyes.
• Redness and watering.
• Strong sensitivity to light (photophobia).
• Swollen eyelids and difficulty keeping the eyes open.
• Blurred or hazy vision, and sometimes seeing halos.
• Spasms of the eyelids.

Why snow and altitude increase the risk

Fresh snow is an excellent reflector of UV, bouncing back a large proportion of the radiation that reaches it, so your eyes receive UV both from above and below. At high altitude, the thinner atmosphere filters less UV; the WHO notes that UV levels increase by roughly 10 percent for every 1,000 metres of altitude. Bright days in spring, when the sun is higher yet snow still lies on the ground, are particularly risky. Cloud cover does not provide reliable protection, because much UV passes through thin cloud.

Mountaineers, skiers, snowboarders, polar travellers and people working outdoors in snowy regions are most often affected. Water, sand and light concrete also reflect UV, although less than snow, so sailors and beachgoers can develop photokeratitis too. Our article on summer eye care covers sun, sea and sand.

Arc eye: welding and artificial UV sources

Welding produces intense UV radiation. Looking at a welding arc without proper protection, even briefly, or standing nearby without shielding, can cause photokeratitis known as arc eye or welder's flash. Bystanders are often affected because they do not realise the danger. The symptoms are the same as snow blindness, usually developing several hours after exposure, often waking people at night.

Other artificial sources include tanning beds and sunlamps used without goggles, some germicidal UV lamps, and halogen or other lamps with broken protective covers. Workplace safety regulations require appropriate shields, helmets with auto-darkening or fixed filters, and screens to protect colleagues. See our page on safety and sports eyewear for the types of protection available.

Treatment and recovery

Photokeratitis usually heals on its own as the corneal surface regenerates, typically within 24 to 72 hours. Treatment focuses on comfort and preventing complications:

1. Get out of the light and rest the eyes in a dim room; wear sunglasses if you need to go out.
2. Remove contact lenses and do not wear them until the eyes have fully healed.
3. Use cool compresses over closed eyes to ease pain and swelling.
4. Use preservative-free lubricating drops to soothe the surface; see our guide to eye drops.
5. Take simple painkillers available over the counter if suitable for you, following the package instructions.
6. Do not rub your eyes, which can damage the healing surface.

A doctor may examine the eye with a fluorescein dye to confirm the diagnosis and rule out other causes, such as a foreign body or infection. In some cases, antibiotic ointment is prescribed to protect the healing surface. Most people recover completely without lasting damage, but repeated episodes are best avoided.

Long-term UV damage

Beyond acute burns, cumulative UV exposure over decades is linked to several eye conditions. This is why protection matters every day, not only on ski trips.

Our guides on cataract and pterygium and pinguecula explain these conditions in more depth.

Children are especially vulnerable

Children spend more time outdoors, have larger pupils and clearer lenses that transmit more UV to the inside of the eye. A significant portion of lifetime UV exposure occurs in childhood. Sunglasses and hats for children are therefore a sensible habit, alongside plenty of outdoor play, which itself has benefits for preventing myopia.

How to protect your eyes

Sunglasses and goggles

• Choose lenses labelled UV400 or 100 percent UV protection, or that meet recognised standards such as EN ISO 12312-1 (Europe) or ANSI Z80.3 (USA).
• Darker is not the same as more protective; UV blocking is a separate property from tint. Dark lenses without UV filters can be worse, because they enlarge the pupils.
• Wraparound frames or side shields reduce UV entering from the sides.
• For skiing, mountaineering and snow sports, use goggles or high-category glacier glasses. Category 4 lenses are very dark and suited to high mountains and glaciers but are not suitable for driving.
• Polarisation reduces glare from snow and water but does not itself block UV.

For a full buying guide, read our article on how to choose sunglasses that truly protect.

Other measures

• Wear a wide-brimmed hat or cap, which can block a substantial share of UV reaching the eyes from above.
• Check the UV index in weather forecasts; protection is important when it is 3 or higher.
• Remember that UV is strong on cloudy days, at altitude and near snow, water or sand.
• UV-blocking contact lenses offer some protection to the cornea but do not cover the whole eye and should be combined with sunglasses.
• Welders and bystanders must use correctly rated welding helmets and screens; ordinary sunglasses are not sufficient.
• Never look directly at the sun, including during an eclipse, without certified eclipse viewers, as this can cause permanent retinal damage (solar retinopathy).

When to see a doctor

Mild photokeratitis often improves within a day or two with rest and lubrication. See a doctor or optometrist if symptoms do not begin to improve within 24 hours, if pain is severe, or if you are unsure of the cause. A growth on the white of the eye or a changing spot on the eyelid should also be checked.