Snow blindness, medically known as photokeratitis, is a temporary, painful eye condition often described as having a sunburn on the surface of the eye. This affliction results from overexposure to ultraviolet (UV) radiation, which damages the outermost layer of the cornea. Although the condition is generally temporary and reversible, the resulting pain and discomfort can be significant. Understanding the causes and employing proper protection are the most effective ways to avoid this painful experience.
What Causes Snow Blindness
Snow blindness occurs when the cornea, the clear front window of the eye, absorbs excessive ultraviolet radiation. The damage is specifically caused by UV-B light, which creates an inflammatory reaction in the corneal epithelium, the delicate outer layer of cells. This injury is comparable to the process of skin developing a sunburn, but it affects the surface of the eye.
The risk of this condition is dramatically increased in snowy environments because fresh snow can reflect up to 80% of the UV light, essentially doubling the exposure. This reflection occurs even on overcast or cloudy days. Furthermore, the intensity of UV radiation increases with elevation, making high-altitude activities particularly hazardous, as the atmosphere provides less natural filtering. While snow is the most common culprit, photokeratitis can also result from UV reflection off water, ice, white sand, or artificial sources like welding arcs and tanning beds.
Choosing the Right Protective Eyewear
Effective prevention of snow blindness relies on selecting and correctly using specialized eyewear that blocks UV radiation. The fundamental requirement for any protective lens is a certification guaranteeing 100% blockage of both UVA and UVB rays, often labeled as UV400 protection. This UV rating is separate from the lens tint or color and remains the primary defense against corneal damage.
Beyond UV protection, the darkness of the lens, measured by Visible Light Transmission (VLT), is crucial for comfort and safety in bright conditions. VLT is the percentage of light that passes through the lens; a lower percentage indicates a darker lens. For typical sunny winter days, lenses classified as Category 3 (S3), with a VLT between 8% and 18%, are recommended to manage glare.
For extreme conditions, such as high-altitude glacier travel or exceptionally bright sunlight, Category 4 (S4) lenses are necessary, offering a very dark tint with VLT typically ranging from 3% to 8%. Polarization reduces glare from the reflective snow surface, but it is a measure of comfort, not a substitute for the mandatory 100% UV protection. The fit of the eyewear is equally important, requiring a design that fully wraps around the eyes or is a goggle style that prevents stray light from entering the eyes from the sides, top, or bottom.
Treating Symptoms After Exposure
Symptoms of snow blindness, such as a gritty sensation, pain, blurred vision, or intense light sensitivity, usually do not appear until six to twelve hours after UV exposure. Once these signs manifest, the immediate priority is to stop further damage by resting the eyes in a dark environment. Moving indoors or into a shaded area allows the damaged corneal cells to begin the natural healing process.
To relieve discomfort, a cold compress or washcloth placed gently over closed eyes several times a day can help reduce pain and inflammation. Lubricating eye drops, commonly known as preservative-free artificial tears, are effective for reducing the painful dry or gritty feeling in the eyes. If contact lenses are worn when symptoms begin, they should be removed immediately and not worn again until the eyes have fully recovered.
Resist the urge to rub the eyes, as this action can further scratch or irritate the already damaged corneal surface. Most cases of photokeratitis resolve completely within 24 to 48 hours. If symptoms are severe, include persistent vision loss, or do not show improvement after two days, a medical professional should be consulted.