Why don't opticians use digital cameras?

Serious question. Well, ok, semi-serious question.

The thing I always find slightly frustrating about buying a new pair of glasses is that I'll be stuck with them for a couple of years, but I can never quite see how I'll look in the new frames until it's too late - there's usually some sort of magnifying mirror available at the opticians, but that never gives me a very clear picture. And while I'm sure the dispensing optician's advice is well intended, I don't always agree with their sense of style...

So, digital cameras. Surely it's the perfect solution? Especially when you consider that most opticians now have a computer or two around.

Try on the new frames. Get a photo taken. Change back to your normal glasses, see how you look in the photo (uploaded to the PC, if possible, or just on the camera screen). Surely that'd work? Or am I missing something?

...although obviously it would have been much more sensible if I'd thought of this at 8:30 this morning and left the house with my camera in my pocket, so that I could have done this before I bought a new pair today. D'oh.

Edit: Ok, so I've just missed all the opticians that do have this facility... *sigh* :)