Lens material and eye safety go hand-in-hand and may not be something most of us pay much attention to during our normal day-to-day activities, competitive sports, or even when visiting your optometrist for new frames. However, the variety of materials that can be used for lenses has increased considerably and will likely continue to expand in future. With choices abound, parents may want to take notice of some of the unique characteristics different lens materials offer before making an informed decision about their child’s new spectacles.
Most modern lenses are variations of plastic (organic) lenses with the most common being CR- 39 (a type of resin). Compared to older glass lenses, plastic lenses are much lighter, more impact resistant and even a bit less likely to fog up.
For younger kids, who are more active and more likely to get a few bumps and knocks from time to time, Polycarbonate lenses are the lens material of choice. It is softer than normal plastic, which means it is also much more likely to absorb the impact of any dangerous blows and will dent rather than crack or shatter. Because it’s generally also a bit more likely to scratch and optically somewhat inferior to other types of plastics, it is often paired with anti- scratch, or glare coatings to even the odds in this regard.
It is important to note that when an ophthalmic lens’ surface is scratched it reduces its impact resistance too. Any surface scratch introduces a weak spot on the lens and creates a type of “fault line”. This can cause stress during impact and makes it more likely to break. It is therefore important to replace scratched lenses used in a high impact environment as soon as possible to avoid potential injury to your eyes.