Can anyone tell me why there is writing on contact lenses?

Question

I've had contacts for years and i just noticed today that there was writing on the lens. It was very small and said like cb... Anyways does anyone else find this wierd? has anyone else ever noticed this?

Answer 1

 I have acuvue night and day contacts and a lens I just found on the ground has CIBA Z646 written on it. CIBA is obvious as it is the company that makes the lens. A google search for CIBA Z646 brings up a lot of science journals with m/z=646 or something occuring at m/z 646. Something to do with peptides and ions? I don't know my chemistry enough, but one article mentioned UV inhibitors and complex polymers. So I think in my case it might have to do with the type plastic or possibly the specific batch of plastic that this lens was made from. So possibly there would be lenses with Z650 or Z643 floating around as the specific m/z value for each batch changed slightly.

Alternatively Z646 indicates a specific model/prescription as a numbering system of Axxx where A is an alpha from A-Z and x is 0-9 there are twenty six thousand possible models. It is a mystery.