[Strabismus, hemianopsia and the sundial of Mawas and Franceschetti].

Unlabelled: THE ARTIFACT: The artifact is a light rectangular slate of black cardboard showing two white lines at 40 degrees angle. It provokes physiological diplopia in lateral vision.

Background: In normal subjects, the right oblique line stimulates the right nasal hemiretina, perceived as an oblique line, and the left temporal hemiretina, perceived as a vertical line, both lines being on the right hand side.