I'm certainly not saying you're wrong, Sft, but it strikes me as improbable that qualified professional people - ophthalmologists, as opposed to the counter-assistants - would permit themselves to be used as "walkin', talkin' mannequins", especially given that the shop they work in is already festooned with hundreds of the frames they want to sell and which customers are free to try on and see how they themelves look in them! Perhaps somewhere on the WWW there's a photograph taken at a conference of opticians - ie where there are no customers to impress. I'd be prepared to bet lots of those attending would be wearing glasses. Consequently, I'd still advise the questioner to "Ca' canny!" (For those of you who aren't Sft, that's "Be careful!" for Scots.)