To get back on topic, the vision provided by a burka is roughly the same as that of a modern motor cycle helmet according to this letter from a motor cyclist in The Idependent.....

Sir: Mr Wedgwood (letters 15, September) may or may not be a racist. However, in trying to explain erratic driving by implying that the driver's vision was impaired because she was "attempting to see through a slot 3cm by 9cm in her burka", he is unobservant. I drive a motorcycle; my head is covered by a helmet and I look through the 11cm by 4cm slot defined by my glasses. Like the burka, they are immediately in front of my eyes and do not restrict my vision at all.

Sam Richmond

East Boldon, Tyne and Wear