Almost 70% of people in the UK wear glasses or contact lenses some or all the time, the third highest proportion in Europe, and this number is steadily rising. 

Safety eyewear suppliers are increasingly providing prescription safety spectacles or goggles to safeguard people’s eyes in the workplace, since ordinary prescription glasses do not offer adequate protection. It is crucial to match the correct lens material to the job in hand, understanding the requirements of the wearer and the hazards they may be exposed to.

CR39

For everyday glasses and users of visual display units (VDUs), CR39 (Columbia Resin 39) lenses made of plastic polymer are commonly used, replacing the glass lenses of old, which were thicker, heavier and shattered easily. 

CR39 lenses offer advantages, such as being lightweight and offering good chemical resistance. However, CR39 does not have the impact strength of new, polycarbonate lenses, and is therefore not suitable for hazardous workplace environments where impact may pose a risk, since it may break and shatter. 

In addition, a UV coating must be added to CR39 lenses to protect the eyes from the sun’s harmful rays that can cause cataracts, macular degeneration or other eye diseases.

CR39 is also thicker than more recently-developed impact-resistant lens materials, making spectacles heavier and distorting the appearance of the eyes, rendering them less appealing cosmetically.

Polycarbonate

Originally developed for the aerospace industry, polycarbonate is now a popular choice for safety eyewear. Made by injection moulding, polycarbonate lenses are up to 10 times more impact-resistant than plastic or glass lenses and give high optical quality. They naturally provide 100% protection from the sun's harmful UV rays without needing a special coating to be added.

Polycarbonate lenses have exceptional strength and resilience and will survive the impact of a steel ball travelling at 160km/h (45m/s) without cracking, chipping or breaking.

They are 25% thinner and 20% lighter than CR39 lenses, making them more comfortable and aesthetically pleasing for the wearer. 

Owing to its versatility and robustness, polycarbonate can be used for rimmed, rimless and half-rimmed spectacles, allowing manufacturers to offer a large choice of lens and frame options to wearers. Polycarbonate lenses are slightly more expensive than CR39 lenses, but remain affordable, and uvex believes their benefits more than make up for this.

Polycarbonate is a relatively soft material, which is what makes it flexible and able to absorb energy without fracturing, so a hard, scratch-resistant coating must be applied to the lens to help protect it and prevent surface scratching before use.

Check your glasses

Prescription lens wearers may not be aware that some high-street opticians will automatically supply eyewear with CR39 lenses unless polycarbonate is specifically requested, potentially leaving them at risk from impact injuries at work. 

You can check your glasses by looking at the lens markings, which will be either at the top or on the side of the lens. Look for the letters ‘S’ or ‘F’. If you can see an ‘S’, your glasses are likely to be CR39.

In conclusion, it is important to ask the optician which lens material will be supplied in your safety eyewear and to ensure it is the right one for you. 

The free uvex RX App (available on itunes) is a virtual assistant that helps wearers of safety spectacles who need prescription lenses to select a suitable product.