Sadly, most people tend to view sports sunglasses as a style choice rather than a way of protecting vulnerable eyes in harsh outdoor conditions.
The real value of sunglasses is to:
- Stop potentially damaging UV rays and excessively bright light from reaching the eye
- Provide a physical barrier to keep out small foreign objects. You don’t want grit or flies in your eyes while you’re running or cycling.
However, the huge variety of sunglasses available, combined with style, marketing and fashion hype, means that choosing the best pair in terms of eye protection is no easy task.
Sunlight, UV, Sports and the Eye
Only 5% of the sun’s energy reaches the Earth’s surface in the form of UV. However the photons of these rays pack a big enough punch to blow apart some of the weaker chemical bonds that hold together biological molecules in the human body.
Your eye is particularly sensitive because not only does it contain many delicate structures, it also has a limited capacity for self-repair.
Most of the harmful effects of UV absorption by the eye are thought to be cumulative over a lifetime. In other words, the damage builds up steadily and does not reverse itself.
Excessive UV-A (tanning) rays can quickly damage the lens of your eye. This can eventually lead to cataracts, where there is clouding over the lens. Meanwhile, the cornea and conjunctiva are especially at risk from UV-B rays (associated with burning).
More reasons to wear sunglasses during sports and exercise
Scientists are also concerned about the effects of large amounts of blue light (from the ordinary visible part of the spectrum) on the retina.
Although this light is not as energetic as UV rays, evidence suggests that routine outdoor exposure over many years to large amounts of blue light (eg. to those participating in water sports), may age the retina and add to macular degeneration in sensitive individuals — the main cause of blindness in people over 60.
If these facts don’t convince you that sunglasses have real merits, then remember also that the delicate skin around the eyes is easily lined and wrinkled by UV damage. Constant squinting in very bright conditions are a sure recipe for ‘crow’s feet’.
And if you do bike or run, you shouldn’t wait to discover the discomfort of having a fly embedded in your eye at 40kmh as you try to navigate your way through twisty lanes or heavy traffic.
Anatomy of Sunglasses
Sunglass lenses both filter light and keep foreign objects out of your eye. There are two aspects to consider when choosing lenses:
Sunglass Lens Materials
The materials commonly used in lenses are glass, polycarbonate plastic and acrylic plastic. Glass tends to give the best viewing quality and is most scratch-resistant. That being said, glass is heavier and more likely to shatter if an object hits it. As a result, you should rule out glass sunglass lenses for sports activities.
Polycarbonate plastic is tougher and more scratch-resistant than acrylic. Additionally, it’s more shatter-resistant than glass and is a good choice for sports sunglasses.
Acrylic plastic can scratch easily but has the advantage of being cheap.
Sunglass Lens Tinting
There are various colours available.
Grey and green lenses are good all-round lenses. They keep colour distortion to a minimum and give a ‘natural’ view of the world.
Amber/orange lenses help filter out blue light. They’re recommended for people who spend extended periods in environments with intense glare such as on snow, water or very high in the mountains.
By reducing blue light transmission, they also tend to improve the clarity of distant objects. This is because your eye is less efficient at focussing blue wavelengths.
Sports Sunglass Terminology
Polarising lenses cut down on the glare due to reflection and are also good in snow and water environments.
Photochromic lenses respond to the intensity of the incoming UV, lightening in dark conditions and darkening in bright conditions. While this is a nice feature, cheaper lenses won’t get very dark. They can also take a long time to adjust to different conditions. They are also unsuitable for driving. After all, most of the UV required to make them ‘respond’ is blocked out by the car windows.
Instead of absorbing light like the other lens types, mirror lenses simply reflect back all or part of the unwanted light. Although they’re very effective in extremely bright conditions, they are often too dark for general use. Also, the metallic coatings scratch easily, so a scratch-resistant coating is a must.
Gradient lenses have permanent shading from top to bottom. They’re useful when you spend a lot of time looking towards the horizon in ‘normal land’ conditions (i.e. not snow or sand).
Sports Sunglass Frames
The function of the frames is to keep the lenses aligned with the eyes as comfortably as possible. Frames should be strong enough to withstand general wear and tear. Look for the following features:
Sunglass Frame Materials
Avoid plastic frames, which tend to crack and break easily. Instead, go for nylon frames, which are very flexible, lightweight and strong. While metal is also a good material, being strong and light, it is not as flexible as nylon. For example, it can bend and break when sat on.
Sunglass Frame Hinges
Allow you to fold the arms flat for compact safe storage. Good hinges are generally made of metal or nylon and contain a spring to keep the glasses snug against your face. The hinge pieces should fit together tightly and shouldn’t wobble or yield when you flex the earpiece up and down.
Nylon hinges should have a metal rod to hold the two hinge pieces together; metal hinges should extend into the earpiece for added strength.
Most manufacturers make different frame sizes. Choose a size that feels neither uncomfortably tight nor so loose it feels like falling off your face.
Sunglass Style and Design
Some frames are of the ‘wraparound’ type. By fitting close to the face, they help to block glare from the sides and top. They tend to be more expensive but the extra protection can be valuable in extreme conditions.
Sport Sunglasses Checklist
- Make sure the sunglasses effectively filter at least 90% of UV-A and 95% of UV-B. The degree of tinting DOES NOT tell you how much they filter UV.
- Higher prices don’t always mean better protection — most sunglasses now on the market block a large percentage of UV radiation.
- For sports and activities, choose polycarbonate lenses.
- Good scratch-protection coatings will extend the life of your sunglasses dramatically.
- Choose the lens tinting type to match your own sports environment.
- Check for visible distortion in lenses before you buy. Put them on and look at a rectangular pattern such as floor tiles. Move your head from side to side and up and down — the lines should stay straight.
- Check that the frames are comfortable for extended periods and that the lenses align with your eyes
- Choose on the basis of function rather than fashion
- Finally, remember that in dark or overcast conditions, using sunglasses reduces your visibility. This is probably not only unnecessary but potentially dangerous too.