Sunglasses aren't just for summer – as the name suggests they're for the sun! In fact, the risk of unprotected eye damage is even greater when the sun's glare is intensified by reflection off large expanses of snow – giving rise to the term "blinding white".
Snow blindness – also called radiation keratitis – may not become apparent until several hours after exposure – typically 6 to 12 hours.
The cornea (the clear front surface of the eye) and the membrane lining the inside of the eyelid can be inflamed by the effect of long exposure to the glare of sunlight from the surface of the snow.
Outwardly the eyes can appear bloodshot and start to water with the level of tears increasing as time passes. To the sufferer it can feel like there is some grit or sand in the eyes and rubbing them will only aggravate the situation.
The level of pain will increase without treatment – reaching an excruciating level in severe cases – and the eyes can swell so much they are forced to close.
In the worst cases, often after repeated unprotected exposure, snow blindness can result in varying degrees of longer-term loss of vision. TheCollege of Optometrists has a full list of the problems that show blindness can cause.
So it is clear how important eye protection is – particularly on the snow slopes and especially at high altitude as the higher you are in the mountains the lower the level of atmospheric filtering of UV rays.
As a rough estimate, every 1,000 feet above sea level results in a 4% rise in UV light intensity, hence the need for good quality sunglasses or goggles.
Sunglasses don't need to come with a costly designer name – expensive often means better but not necessarily.
The key to protection from UV light is the CE mark. This ensures the lenses conform to the European Community Standard and are comparable to the British Standard BSEN1836.
By placing the CE marking on the sunglasses the manufacturer is declaring the product conforms with all relevant essential health and safety requirements. For more advise on CE marking check the UK government website here.
The CE mark ensures the glasses will provide high levels of protection against damaging UV light.
And bear in mind that not all UV light is the same. There are three types of UV radiation. UV-C is easily absorbed by the atmosphere and presents no threat but the higher wavelength UV-A and UV-B radiation can affect the eyes and vision. The best lenses will block 100% of all UV-A, UV-B and harmful blue light.
The UK government blog has some excellent advice on what you need to know about ultra-violet light and vision.
Don't confuse the shade of the lenses with their ability to filter UV rays and be aware that damage can occur even when the sun is covered – UV rays can filter through the clouds and remain harmful.
For skiing, the additional attributes to look for are polarising lenses which will reduce reflective glare from the white snow surface and anti-reflective coatings which will also eliminate glare but only by reducing the total amount of light reaching the eye.
Also, impact resistant lenses are essential if you are engaged in active sports and larger lenses will increase protection as will wrap-around frames as they keep out peripheral glare and provide added protection from indirect light exposure.
Ultimately you will often get what you pay for and, if you have opted for a pair of sunglasses for skiing that encompasses all of the above attributes, you might find you've paid a bit more than you had originally intended.
The good news is that glasses repairs are generally not expensive and very quickly done so if your glasses do incur any damage you will be able to get them as good as new and your original investment will see you through many ski seasons.