glasses

[dondons]

I have just got a new pair of glasses from Boots and if you look carefully, you can see, embedded in the lens a small circle on the top and a 22 undeneath .They are extremely small and difficult to see and of course when wearing them I am not aware that they are there. Can anyone shed any light on why they are there and what is the significance of them?

[Librarians4]

I wear vari-focals and have always assumed my own set of symbols and numbers are connected with the strength of my prescription, or the curvature of the lens, or the location of the reading bit of my lens. Shall ask my optician next time I pass by the shop!

[Whickerman]

I worked for 15 years in opthalmic production, so I can tell you exactly what that is!

Most companies today make lenses from plastic monomer, which is poured into a glass mould. The power of the lens depends on the shape of the mould, and the type of monomer used (as each has a different refractive index) - bear with me, i'm getting to it!

Now, this allows the production of varifocals etc. Each factory has a wide range of lenses, and also many factories produce for lost of different companies - for instance, the Pentax lenses you get in Specsavers are produced by Carl Zeiss Vision (Formerly Sola Optical).

So, each lens in some ranges will also have both the power and logo of the recipient company on them, in tiny script. Most will actually have two logos - one on either side. This is applied either at moulding level, or with polyacrbonate lenses it's added using a laser. This allows the optical technician line up the power of the lens correctly when it is being glazed to go into your frames. Most people never notice this - in fact, in most cases people have a hardcoat added for scratch resistance and the mark is rendered almost invisible.

What you're seeing - the circle - probably has another mark either in or through it. This also helps identify the make and model of each lens to help trace the manufacturing company if anything goes wrong. The 22 is either a model code, or there's actually a 5 after that, as the power of varifocal lenses jumps in steps of 25.

[dondons]

what a GREAT answer Whickerman!! It tells me all that I wanted to know. Many thanks