They’re usually thick-framed or with thick earpieces so they can fit a tiny spy camera in there, as opposed to transmitting whatever passes through the lenses (as is implied in the episode.
Honestly, I want a prescription pair, but I don’t have the money.
This scene is why I’m 100% convinced the Doctor Who writers read our tumblrs. That and “The Pretty One” scene in “The Doctor’s Wife.”
(Of course there was never any doubt in my mind that Neil Gaiman reads about himself on the internet. Wouldn’t you, if you were Neil Gaiman?)