BS EN ISO 8624:2020 pdf download.Ophthalmic optics – Spectacle frames – Measuring system and vocabulary.
3.1 Principal terms of the boxed lens system 1)
3.1.1
boxed lens system
system of measurement and definitions of spectacle frames based on rectangular boxes that
circumscribe the lens shapes and that are used for the determination of the dimensions of the spectacle front and in which the upper tangent is both common to the right and left lens shapes and regarded as being horizontal
Note 1 to entry: In the case of spectacle frames having a significant face form angle, the line touching the uppermost edges of the right and left lens shapes shall be regarded as horizontal.
Note 2 to entry: For measurement of a lens aperture, the measurements should be taken as if projected onto the base of the rectangular box which is regarded as being tangential to the plane of the lens shape at its boxed centre. This plane is close to that formed by the upper and lower tangents to the lens shape. For frame measurements, the aperture is taken to be the size of the hypothetical lens that fits the frame. Measurements to the apex of the groove or equivalent can give slightly different values.
Note 3 to entry: Since the tangent common to the right and left lens shapes is regarded as being horizontal, the lines at right angles to it, e.g. the two sides of the box either side of the lens shape, are called "vertical". While the frame is worn, the horizontal lines will remain horizontal if the head is held erect, but the vertical lines will frequently not be vertical but, although in a vertical plane, will have their lower ends tipped in towards the cheeks (see the as-worn pantoscopic angle in ISO 13666).
3.2.14 side angle, en GB angle of side, en GB frame pantoscopic angle, en US angle in the vertical plane, when the side is opened, between the perpendicular to the plane of the spectacle front (3.2.11) and the line joining the middle of the joint to the point on the lower edge of the side that is assumed to make contact with the top of the ear Note 1 to entry: When the spectacle frame is of semi-rimless or rimless construction, the reference line should be taken as the line joining the rear surface of the upper and lower edges of a plano or demonstration or dummy lens along the vertical centreline. Note 2 to entry: Unless otherwise stated, the side angle is regarded as positive if downwards from the perpendicular to the reference line. Note 3 to entry: In dispensing, the reference line is to the back surface of the rims, but in frame design, it is to the apex of the groove or equivalent. There can be a difference between the two resulting angles of up to 1,5°. Note 4 to entry: See Figure 9.BS EN ISO 8624 pdf download.