MULTI-FOCAL SPECTACLE LENS WITH A DIOPTRIC POWER VARYING PROGRESSIVELY BETWEEN DIFFERENT ZONES OF VISION

摘要

of the disclosure The invention contemplates a multi-focal spectacle lens with a dioptricpower varying progressively between different zones of vision (progressive lens). The principal sight line, i.e. the line connecting the penetration points of the lines of sight for different object distances is a curve swung toward the nose of the wearer. In order to enable a pleasing binocular viewing for the spectacle wearer the progressive surface of the lens is horizontal symmetric with respect to said principal sight line. The progressive zone lying between the far-vision zone and the near-vision zone of the lens is short and within this zone astigmatism exists along the principal sight line within the scope of a permissible reduction in vision. Within the progressive zone and the near-vision zone the distortion caused by the prismatic powers at points of the nasal region and temporal region which correspond to each other is so selected that the horizontal and vertical directional errors do not exceed tolerable values. In this way the wearer will see an equally sharp or an equally blurred image of the object with both eyes while binocularly non-harmonizing directions of sight are avoided so that the fusion of the eyes is convenient for each object distance.