1) 100 % protection from harmful ultraviolet radiation.
Some lens materials absorb more UV than others.
High index materials, used in high prescriptions to reduce edge thickness, absorb 100% UVA and UVB
Standard plastic lenses require an added UV coating to ensure 100% protection from UV radiation.
A specialized UV anti-reflection layer can be added to the back surface of the lens to act on reflecting UV light that comes in from the side and from above the lens from the eye.
Tints reduce ambient light but without a specific UV coating it does not cut out 100% of harmful radiation.
Dark lenses with only a scratch resistant coating do not afford 100% UV protection.
Plastic photochromatic lenses absorb 100% UV.
The colour of the tint varies according to personal preference and according to the particular outdoor pursuit.
No single colour has better protection than another. The darker the tint the less ambient light will pass through the lens.
Tinting a lens reduces ambient light but does nothing for discomfort (squinting your eyes) and disability glare (forcing eye closure).
Surfaces like water, snow or wet road reflect light and cause these types of glare.
These surfaces also increase the amount of UV hitting the eye directly and indirectly leading to an increase in skin and eye damage.
So polarization and a 100% UV coating are the ultimate in sun protection.
4) Sunglasses that are wrapped and fit close to the face are ideal.
This will reduce the amount of light reaching the eye.
HOW DO YOU KNOW WHAT YOU ARE GETTING
If you are buying sunglasses off the shelf check the UV Protection Rating.
Sunglasses bought in Australia are required by law to display a UV Protection Rating from category 0 to 4. Category 0 and 1 provide limited UV protection and category 2, 3 and 4 provide a high level of UV protection. There is an alternative system that gives an Eye Protection Factor (EPF) between 1 and 10.
EPF of 9 and 10 implies 100% UV Protection.
When comparing the 2 systems any EPF rating equates to category 2,3 or 4 sunglasses which all provide a good to high level of UV protection.
Windsor Optometry uses Crizal UV Forte anti-reflection coating which is applied to the front and back surface of the lens so our optical lenses with the coating blocks out 100% UV radiation . So without applying a dark tint our lenses are highly protective. When prescribing prescription sunglasses we just add a tint and preferably polarization and our patients have the ideal pair of sunglasses.