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

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.

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. Likewise, the left oblique line is seen as two lines on the left hand side. The 4 lines form and M and a W combined. The strabismus subject sees 3 lines for he neutralizes one; the alternating squint sees only 2; the heterophoric sees 4 lines, two of which blurred, and the hemianopic sees only part of the dial.

The subject must select the image he sees from an array of possibilities shown on the back of the dial. From 5 years of age on, normal subjects select the [symbol: see text] or the "butterfly"; hemianopic subjects correctly describe the loss of either the left or right field.

The sundial facilitates both the screening and the treatment of binocular vision disorders. Bangerter's hemifilter will be used in association with exercises for physiological diplopia at home under monthly orthoptic control. All this made it possible to obtain useful peripheral fusion in early onset strabismus.