It's the same with contact lenses. The first time I needed lenses, I asked, "How can I get contact lenses?" Expecting to have to set an appointment with an opthamologist, pay for an exam (which I had 6 months ago), and order the lenses.
The girl at the counter just asked, "What's your prescription?"
I told her, "I don't have one, but I know I'm a -2.0."
She said, "So your prescription is -2.0?"
"Yes. But I don't have the prescription that says that."
"You just told me your prescription was -2.0. What do you mean you don't have it?" She looked at me in confusion.
I was thinking of the golden little ticket with the opthamologist's chicken scratch stating it was -2.0. "I don't have the paper."
She just laughed, "You don't need a paper. You know you need -2.0, right?"
She pointed behind her to the sacred boxes filled with prescription contact lenses, "Do you want the six-pack or the twenty four?"
That easy. Just tell them your prescription, and voila the contacts are yours.