The EN166 standard specifies the eye or face wear needed, dependent on the risk you are working in.
The standard covers:

Mechanical Strength.
Strength is determined by subjecting the product to an impact with a steel ball. The higher the impact velocity the higher the mechanical strength, the letter you will find on the lens or frame of the product will let you know what impact velocity the product has been tested to.

Field of Use.
Used to describe what substances you may be working with or around. The number printed on the lens or frame will allow you to determine what substances you can work with.

Optical Performance of class.
Relates the lens material quality. All BOC eye and face products have an optical performance of 1, the highest class possible ensuring your eyes are not subjected to unnecessary strain.

Other European standards for eye protection
EN169 “Welding filters”
EN170 “Ultraviolet filters”
EN171 “Infrared filters”
EN172 “Solar protection filters for industrial use”
EN175 “Welding work equipment”
EN207 “Glasses for laser protection”
EN208 “Glasses for laser adjustment”
EN379 “Specification concerning welding filters”


Additional Information
Choosing the right eye protection
Safety spectacles - Lens guide