Lens materials and coatings explained
Getting your prescription is just the beginning of your glasses-buying choices. Our experts explain lens materials and coatings, with tips to keep the cost down.
Our research shows that when you're buying glasses you don’t always understand whether different choices – such as lens coatings – are necessarily right for you. We’ve quizzed expert opticians for their advice on choosing the right specification glasses.
Lens materials explained
Resin lens materials
Why? For safety, as they offer high impact resistance. Most glasses are plastic, but lightweight resin materials are stronger, with a wide variety of sports tint options. They don’t suit high-index (thinner lens) prescriptions, and they scratch easily. Polycarbonate brands include Trivex (also known as Hoya PNX, Trilogy, Specsavers Supertough). They’re good for children’s glasses, and rimless or extra-robust glasses for adults.
Tip: Ask whether an anti-scratch coating is included.
Why? So you don’t need separate sunglasses. These lenses are clear indoors, but – activated by UV light – become sunglasses outdoors. Brands include Reactions, Transitions, Colourmatic and Photofusion.
Tip: Ask your retailer how quickly the lenses change – they may take up to 5-10 minutes (typically 2-5 minutes) – and how dark they will go. These lenses don’t work as well in cars, and can go dark unexpectedly. Newer designs are claimed to change faster.
Your prescription will determine how your lenses will look. If you are short-sighted, the thickness will be on the edge of the lens, and choosing a higher-index material will result in a thinner and slightly lighter lens. The higher the index, the thinner the lens.
Why? Thinner lenses for prescriptions that normally require thicker lenses. Typically those who are short-sighted with prescriptions over -5 will benefit, but they are also worth considering for -2 and above. This type of lens can also lead to more reflections on your lenses.
Tip: Choose your frame wisely to avoid paying for higher-index (thinner) lenses. Frames with a pupil distance that’s close to your own, and smaller frames (such as small, round frames rather than a large aviator shape) naturally reduce lens thickness.
Aspheric design lenses
Why? These have a more complex (flatter) surface profile to minimise lens distortions, and a thinner, lighter lens that magnifies your eye less. This makes them good for long-sighted and age-related reading prescriptions. If your lens has a prescription of over +2.00, consider combining with a naturally thin minimum-edge surface.
Tip: Don’t panic if they feel strange at first, as they can take time to adjust to.
Why? Also known as bespoke or freeform lenses, these are good for unusual prescriptions, high astigmatism, large or small pupil distances, or uneven eyes. For these lenses, extra measurements are taken, then the lens is optimised for your particular eyesight, using the highest-quality lens optics.
Tip: Ask lots of questions if you’re offered these, as they may make little noticeable difference, especially for average and low prescriptions.
Lens coatings and tints
Blue light blocker
This layer absorbs blue light – from computer screens, for example. Claims include protection from eye conditions and strain.
Tip: More scientific evidence is needed to establish a link between harmful blue light and retinal damage and – if so – whether reducing it helps.
Increases lens durability. This hard, thin resin coating comes as standard with some regular lenses, or with an anti-reflection coating.
Tip: Won’t make a lens completely scratchproof, so still take care.
Reduces image ghosting, makes your eyes more visible and lets more light through – but the key disadvantage is that smudges are also more visible. Especially useful for high-index lenses and driving at night.
Tip: Increasingly comes as standard.
Combines scratch-resistant UV, anti-reflective, hydrophobic (water-resistant) and oleophobic (repels dust and grease) properties. Costs around £75 extra.
Tip: Ask about the guarantee – some are as long as two years.