Most sunglasses transmit some visible light and block substantial amounts of harmful UV. Overexposure to UVB can damage the retina, cornea, lens and conjunctiva and other eye diseases, so reducing the amount of UVB reaching the eye can substantially improve long-term eye health.
Manufacturers of sunglasses are not compelled to follow standards for the amount of sunlight (visible and UVB) transmitted through the lenses. Consequently, cosmetic sunglasses may allow significantly higher percentages of UVB through than special purpose lenses. Care must be taken when selecting a suitable pair of sunglasses, and price or brand may not be a guarantee of quality regarding UVB protection.
Some researchers believe that the shape of the sunglasses is more important than the amount of UVB protection, claiming that the majority of ocular damage occurs from scattered or reflected light entering through the side of the glasses. Sunglasses with side protection can be purchased on the Cancer Council website or from companies like Bollé. However, if it’s not possible to use glasses with side protection, look for a pair with lenses that cover the sides and sit close to the face.
Sunglasses are crucial when snow shoeing or skiing. Snow reflects UVB extremely effectively, and this reflected sunlight can be as damaging to eye health as direct sunlight. Sunglasses also provide protection from bright sunlight on the horizon. During winter, the sun moves closer to the horizon and sunlight is more likely to shine into the eyes. While the amount of UVB that penetrates the atmosphere decreases considerably when the sun is on the horizon, sunglasses improve comfort substantially for the user.
When selecting a pair of sunglasses, consider these aspects.
Aim for sunglasses that blocks 99% of UV and blocks both UVA and UVB. Such sunglasses are labelled UV400.
These reduce glare from shiny surfaces such as snow, glass, and water, making it easier to see. Quickly test if sunglasses are polarised by examining the intensity of a shiny image (e.g. a computer monitor) through the sunglasses when they are held normally, and when they are turned vertically. If the reflection changes, then they’re polarised. There’s another method that can be done with one known polarised lens such as a camera filter and one that’s being tested. Hold them to the light and rotate one through 90 degrees. If the test lens is polarised the light will go black.
Select lightweight materials as heavy frames can give some people a headache.
Titanium is a durable but expensive option. Sunnies are all too easy to break or lose in the bush, so opt for something that’s relatively inexpensive to replace.
A cord attached to both arms can hold glasses securely in place, stopping them getting dislodged or lost accidentally. Alternatively, glasses with arms that wrap around the ears to keep them in place are sufficient.
For protection from peripheral radiation.
Some prescription glasses can be made with tinted lenses which help absorb light before hitting the user’s eyes. Although not as effective as polarised lenses at reducing glare, they do offer reasonable protection, and some people find this an easier option than contact lenses and sunnies.
To sum up, bushwalking sunglasses should be lightweight and comfortable, perhaps secured to the user’s head or body so the sunnies are hard to lose.