Multi-focal spectacle lens having at least one progressive surface

Abstract From the Canadian patent

A multi-focal spectacle lens having two progressive zones which are spatially separated from each other and which provide smooth transition of dioptric power from one to the next of three different viewing-distance regions. This progressive surface is calculated in accordance with the technique of spline analysis and is twice continuously differentiable. Such a progressive lens which is illustratively described for use at computer-screen work stations, has an upper viewing-distance region designed for distant vision, a middle viewing-distance region designed for viewing the computer screen as well as a document arranged alongside the screen and a lower viewing-, distance region designed for …