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© Rodenstock GmbH
Status: September 2023
Figure 6-7: Eye's rotation center requirement (ECR) and CVD
▪ Pantoscopic tilt R/L (PT):
Definition according to DIN EN ISO 13666: Angle in the vertical plane between the optical axis of a spectacle lens
and the fixation line of the eye in primary position, which is usually assumed to be horizontal. The optical axis is
vertical on both surfaces of the lens. For aspheric surfaces, there is no optical axis according to this definition
(Figure 69).
Figure 6-8: Pantoscopic tilt
▪ Face form angle (FFA): Definition according to DIN EN ISO 8624 and DIN EN ISO 58208: Angle between the
frame plane and the right or left lens plane. The lens plane is the plane through the horizontal and vertical
centerline in the right and left box system of the spectacle frame, respectively. The frame plane is the plane
passing through the mutually parallel vertical centerlines of the box systems defining the right and left lens
planes of an eyeglass frame (Figure 610).
Figure 6-9: Face form angle
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