This may be of interest. This is a high end shooting glasses frame. The circle holds the lens, the black patch distrupts the vision from the left eye. I have seen light patches rather than black and in some cases just a stick like a matchstick.
http://www.stewardsportsglasses.co.uk/images/championworld4640.jpg
Me I am low cost. I wear normal glasses with the lens adapted to be ideal towards the top left of the right lens and a light cream coloured perspex attached to the sight that covers the forward vision of the left eye.