The most important factor when buying a pair of sunglasses is to ensure they offer full protection from both UVA and UVB radiation. If you are going to be wearing sunglasses for long periods of time whilst running or walking and you are working up a sweat, then you also need to consider comfort, fit, anti-fogging and lens tint.
Specialist running glasses now feature non-slip nose pads, super-lightweight adjustable frames, interchangeable lenses and careful design to ensure ventilation and prevent fogging.
If you are going to be running in different conditions then you need to consider purchasing sunglasses with interchangeable or polarized lenses to cover all your needs.
Dark Tints: blue/grey/green/brown are good for bright and sunny conditions and are most comfortable for the eyes in harsh light.
Golden Tints: yellow, gold and amber tints are better for low-light conditions as they filter out the blue light and make it easier to see the bumps and edges in the terrain.
Polarized/Photochromic: photochromic lenses are great for very bright conditions as they cut down on the glare from the sun reflecting off salt flats and sand. However, their base colour tends to be darker than normal lenses and so towards the end of the day they may become too dark to use as the shadows grow longer.
Mirrored lenses: enhances the effectiveness of a tinted lens by reflecting sunlight bouncing off the ground, therefore reducing glare.
Clear: Use in dark or windy conditions when you want to reduce your eyes from tearing when running.
You should buy sunglasses that protect against both UVA and UVB radiation. Too much exposure to UV over a short amount of time can cause photokeratitis, which is basically sunburn to the eyes. Long-term exposure to UV rays can cause permanent damage, so ensure that your sunglasses offer full protection. This is especially important in sandy deserts or on salt flats where the sun will be reflected off the ground almost as much as if it were snow.
In humid and rainy conditions or where you will be working up a sweat you want to choose frames that offer good ventilation to prevent your sunglasses from fogging up. Choose a set of frames that hold the lenses away from the face so that air can circulate freely, and consider anti-fog coatings.
If you are taking part in sporting activity it’s sensible to make sure that your lenses are made out of a shatter-resistant material, a polycarbonate rather than traditional glass or plastic for example. Also consider what the frames are made out of – the more flexible the less likely they are to break when dropped or squashed into a fully packed race backpack.
Also consider the fit and comfort of wearing your sunglasses for a long time, you want something lightweight, maybe with rubberized nose-pieces and potentially with adjustable earpieces to keep the glasses in place when running.