Frame Measurements and Markings PDF

OPHD 2604 Frame Measurements Chapter 2 7 February 2024 Frame measurements systems: Frame measurements are essential for the proper ordering of prescription glasses Frame measurements is also essential when ordering a replacement for a br...

OPHD 2604 Frame Measurements Chapter 2 7 February 2024 Frame measurements systems: Frame measurements are essential for the proper ordering of prescription glasses Frame measurements is also essential when ordering a replacement for a broken part TWO SYSTEMS: important to allow the accurate placement of the optical centres of lenses and bifocal segment heights 1. Datum system (earlier) 2. Boxing system (more recent)  Frame measurements systems: 1. Datum System: This system is based around the datum line Two horizontal lines are drawn at the highest and lowest edges of the lens. A line drawn halfway between the two horizontal lines and parallel is known as the datum line This system is no longer the preferred system of manufacturers and has been officially replaced by the boxing system in the international standards  Frame measurements systems: Datum line: ― Refers to the horizontal line midway between the horizontal tangents to the upper and lower peripheries of the lens. Datum centre: ― Refers to the point C lying equidistant between D and D’ ―Point half way between the edges. Mid-Datum Depth: ― Refers to the vertical line through C from points E to E’. Datum Lens Size: ― Is given in terms of the datum length and the mid datum depth i.e. DD’ and EE’ (eg. 46x40). Datum frame size: ― With dash or slash, between eye size and bridge size. Eg. 54 -18 or 54 / 18.  Frame measurements systems: 2. Boxing System: Improvement over the datum system The datum system used two horizontal lines, one against the top and the other against the bottom of the lens With the boxing system vertical and parallel tangents added to either side of the lens, forming a box  Frame measurements systems: COMPONENTS of the Boxing System: 1. Horizontal midline - The horizontal line halfway between the top and bottom of the lens 2. Geometric center - The center of the lens ― The point on the horizontal midline halfway between the two lens bordering vertical lines ― This term does not imply anything about the optical positioning of the lens  Frame measurements systems: COMPONENTS of the Boxing System: 3. Size: The size of the lens is the length and depth of the box containing the lens The horizontal length is referred to as the eye size when referring to the frame and the lens size when referring to the lenses Both are measured in mm  Frame measurements systems: COMPONENTS of the Boxing System: 3. Size: A-Size: ―Horizontal measurement of the lens ―Refers to the eye size or lens size B-Size: ― Denotes the vertical measure of the box enclosing the lens Both “a” and “b” are in a sense independent of the lens shape  Frame measurements systems: COMPONENTS of the Boxing System: 3. Size: C-Dimension: ― Refers to the width of the lens itself along the horizontal midline ―The “C” dimension of a lens is seldom used ― Can vary considerable from the “A” dimension ― “C” dimension is not the same as “C” size of the lens “C” size of a lens is the circumference of an edged lens Frame measurements systems: COMPONENTS of the Boxing System: 4. Measurement: To determine the horizontal boxing dimension of a FRAME: ― Measurement begins at the inside of the groove on the left side and extends horizontally across the lens opening to the farthest part of the groove on the right side of the box To determine the horizontal boxing dimension of a LENS: ― Measurement begin at the apex, or point, of the bevel on the left side of the box enclosing the lens and extends to the apex of the bevel on the right side of the box  Frame measurements systems: COMPONENTS of the Boxing System: 4. Measurement: To determine the horizontal boxing dimension of a FRAME: We cannot see the inside groove of the frame = we must ESTIMATE where it will be and hold the ruler so that the 0 point is at the position of the groove on the left side If you only measure the the opening of the frame, you need to add ½ mm to your measurement per side = add 1mm in total  Frame measurements systems: COMPONENTS of the Boxing System: 4. Effective diameter (ED): Found by doubling the distance from the geometric center of the lens to the apex of the lens bevel farthest from it This measurement helps determine the smallest lens blank from which the lens can be cut The longer the effective diameter is, the thicker the finished lens will be  Frame measurements systems: COMPONENTS of the Boxing System: 5. Frame Difference: The difference between the horizontal and the 20mm vertical measurements is known as the frame difference Measured in mm The larger the difference, the more rectangular the enclosing box appears 10mm Frame difference is sometimes referred to as lens difference  Frame measurements systems: COMPONENTS of the Boxing System: 6. Distance between LENSES (DBL): Distance between the two boxes when both lenses are boxed off in the frame Measured on the frame as the distance from the inside nasal eyewire grooves across the bridge area at the narrowest point Measured in mm Two frames having the same DBL will not necessarily fit the person in the same manner because of variations in lens shape  Frame measurements systems: COMPONENTS of the Boxing System: 6. Distance between LENSES (DBL): Again, we cannot see the groove on the inside of the frame = ESTIMATE the position Alternatively: measure the distance from the lens opening to the other lens opening and then subtract 1mm (½ mm each side)  Frame measurements systems: COMPONENTS of the Boxing System: 7. Geometric Center Distance (GCD): GCD is known as the distance between the two geometric centers of the lenses Also known as the FRAME PD Calculated by adding the eye size to the DBL (The result is the same as the measurement) Also known as: 1. Distance between centers (dbc) 2. Frame center distance 3. Frame pd The term ‘frame PD’ is commonly used but has NO relationship to the wearer’s PD measurement Frame measurements systems: COMPONENTS of the Boxing System: Px PD vs Frame PD vs Spectacle PD Patient actual PD = eg. 65mm Frame PD = GCD / eye size + DBL Spectacle PD = eg. Ready made readers will have a PD (might not respond to patient PD) ― Why is this significant?  Frame measurements systems: COMPONENTS of the Boxing System: 8. Seg height: When specifying bifocal or trifocal segment height, the reference points are given in mm as either: 1. Seg drop/raise - The distance below or above the horizontal midline 2. Seg height - The distance from the lower line of the boxing system rectangle enclosing the lens shape In the measuring process, the level of the lower line of the box corresponds to the lowest point in the eyewire groove This level may be different from the depth of the point on the lens edge found directly below the pupil Temple length: Temples are marked with the total, or overall, temple length Temple length may be expressed in millimeters Temple length measurements: 1. Overall temple length 2. Length to bend (LTB) 3. Front to bend (FTB) Temple length: 1. Overall temple length: This is the distance from the center of the center barrel screw hole to the to the posterior end of the temple, measured along the center of the temple When measuring the overall temple length, it is necessary to measure around the bend and not in a straight line, unless the temple is straight Temple length: 2. Length to Bend (LTB): An older method of measuring temple length is in terms of the length to bend (LTB) This is measured from the center of the barrel to the middle of the bend The distance from the middle of the temple bend to the end of the temple is known as the length of drop Temple length: 3. Front to Bend (FTB): If there is a turn back end piece, there is a distance between the plane of the frame front and the actual beginning of the temple It can be specified as frame to bend (FTB) which would be slightly longer than LTB This measurement method is seldom used Frame Markings: Most frames are marked with three measurements: 1. Eye size 2. DBL 3. Temple length metal frames that are manufactured from “rolled gold” are also marked as to the amount of gold found in the frame Frame Markings: 1. Eye-size and DBL: When a frame is marked 50□20, it means that the eye size is 50mm and the distance between lenses is 20mm ― The box between the numbers means that the eye size is measured according to the boxing method ― It also serves to separate the two numbers and prevent confusion The eye size and DBL are sometimes marked as: ― 50–20 ― 50 / 2  Frame Markings: 2. Location of the markings: 2. Location of the markings: PLASTIC FRAME: METAL FRAME: On the inside of the nose pad On the upper outer section of the eye The eye size and DBL are wire usually on the inside of the The size printed on the back side of the bridge end piece They are sometimes printed Sometimes the eye size is printed on one end piece and the DBL on the other on the underside of a top Temple length is found in the inner side reinforcing bar of the temples They are also printed on the Some manufactures put all three temples measurements on the temple Frame Markings: Other possible markings: Frame should be marked as to: Country of origin Manufacture Frame name ― Many frame manufacture use a number rather than a name ―This can be confusing if the frame colour is also specified by numbers ▪ Frame colours usually have a capital ‘C’ followed by a number (eg. C23) ―Consulting a frame reference catalogue or database will help Frame Markings: Safety Frame Markings: Frames that are suitable for use as safety glasses must have “Z87” or “Z87-2” and the name or logo of the manufacturer stamped on the frame front and on both temples This is as specified by the ANSI (American National Standards Institute) The standard is numbered as Z87.1 If a pair of glasses has safety lenses, if it is not marked by Z87 or Z87-2 it means that the glasses are not safety glasses Gold Classification: Type: Meaning: Fine Gold 100% pure gold Solid Gold Gold plus base metal evenly mixed throughout Gold Filled Base metal inside a solid gold coating Gold Plating A base metal thinly plated with gold Gold Flashing A base metal with gold thinly and quickly applied in a manner similar to that of gold plating SELF REVIEW Page: 22 END