Well, I assume they're women.
On Tuesday, someone wearing a black burka with an extremely thin eye-slit walked past me carrying a cup of Starbucks™ coffee. I then proceeded to spend far more time than was sensible wondering how a person wearing a burka manages to drink coffee in public without revealing their face. As I thought about the problem in depth, I found myself conjuring up various contraptions involving drinking straws' passing through eye-slits.
I think I might have spotted a gap in the market—and a market in the gap.
Postscript: Actually, having now consulted this useful BBC graphic, I think the person was wearing was a niqab, not a burka. The title of this item stands, however, as I'm rather proud of the pun (eye-slits, peerage, geddit?).