At Buckingham Opticians we can supply all types of plastic lenses, from ordinary CR39 to high index 1.74, including tints, polarising filters and the latest generation of plastic photochromic, Transitions Signature.

There is a wide range of plastic materials available.  The most commonly used material is CR39 (Alyl Di-Glycol Carbonate), a thermosetting polymer which has excellent optical properties, but it can scratch a little too easily and in higher lens powers can be quite thick.

If you have a higher prescription or are conscious of the thickness of the lenses, thinner lens designs are available.  Materials with a higher refractive index bend (refract) the light more, so tend to be flatter and thinner than conventional CR39.  The higher the refactive index, the thinner the lens.  So-called Hi-Index lenses are available in 1.6, 1.67 and 1.74.  However, the higher the refractive index, the more light is reflected from the front and back surfaces, making them appear more 'glassy'.  So we usually recommend the use of a Multi-Layer Anti-Reflection coating (MAR) with these materials, which greatly improves the cosmetic appearance of the lenses, and also makes them more scratch -resistant.

At Buckingham Opticians we use Transitions 8 as our plastic photochromic lens material of choice.  The lenses are clear indoors, in the car and at night, but adapt quckly to sunlight to protect the eyes from glare.  They also offer 100% protection from harmful UV light.  They are available in brown, green and grey.

For those who need protection from glare when driving, the alternative is Transitions Xtractive, which carry a moderate tint in the car and indoors, but also rapidly adapt to sunlight when outside.  They also offer 100% protection from UV.  They are also available in grey, green and brown.

For drivers and anglers, there is also the Transitions Xtractive Polarising, which eliminate glare through a combination of a light sensitive tint and a polarising filter.  They are only available in grey.

DRIVEWEAR.  These lenses react to visible light as well as UV, which means they change in the car and indoors when the lighting is bright.  They also have a polarising filter which eliminates glare inside and out - unlike conventional polarising filters these do not appear darkly tinted, so they can be worn in comfort indoors.  In low lighting the lenses have a green/yellow colour, improving contrast and maximising visual efficiency.  As the lighting increases they change to a copper colour, which is great when driving and may inprove depth perception, and then to a dark red/brown in bright sunshine.  However, as the lenses always have a certain depth of tint, they are not designed to be worn when driving at night.

In rimless spectacle frames, the bridge and sides are fitted to the lenses by bolts or gromits which are fitted into holes drilled through the lens material.  As a result the material used must be tough and less brittle.  Obviously glass - even toughened glass - cannot be used as it is far too brittle (and illegal!), but even CR39 is not recommended as it can break easily.

We recommend the used of polycarbonate (1.59), Trivex (1.53), 1.6 or 1.67.  Polycarbonate is the material from which bullet-proof glass is made.  It is tough and durable but can crack if the mounts on the rimless frame are overtightened.  Trivex is more expensive, but is virtually unbreakable and comes with a manufacturer's two-year warranty against breakage.  1.6 and 1.67 are also virtually inbreakable, and are especially suited to higher prescriptions.  Tints, polarising filters and Transitions 8 and Xtractive are all available.