Walters and Meinel were clear about the historical significance of Walters’s discovery ["double vision"]. In his words: ‘in vision itself little advancement has been made since the adoption of perspective by artists some centuries ago. Consequently all pictures in existence, without exception, are painted as though their creators had only one eye in their heads, similar to a Cyclops’. (http://www.tate.org.uk/research/publications/tate-papers/23/as-seen-modern-british-painting-and-visual-experience)