Frame measurements

Different Measurements of Frame and its Markings. Exciting quiz at the End.

1. Frame Measurements Mayuri Mohite B.Optometry

2. Familiarity with Frame measurements and frame markings is essential to proper ordering of prescription glasses.

3. The previously used datum system for measuring lenses was established as a system of reference points for frames and lenses so that placement of lens optical centers and bifocal segment heights would be consistent. H orizontal lines were drawn at the highest and lowest edges of the lens Older Datum Syste m

4. A line drawn halfway between the two horizontal lines and parallel to them was known as the datum line. The width of the lens along this line was called the datum length or eye size. The point along the datum line halfway between the edges of the lens is the datum center. The depth of the lens, measured as the vertical depth through the datum center, was the mid-datum depth. Markings

5. Boxing System The datum system preceded the currently used boxing system.

6. A horizontal line halfway between the top and bottom of the lens. I n the boxing system, this line is more commonly referred to as the horizontal midline or the 180degree line. Horizontal Line

7. The center of the lens is the point on the horizontal midline halfway between the two lens-bordering vertical lines. It is known as the geometric center or boxing center of the edged lens. This term does not imply anything about the optical positioning of the lens. Geometric Center

8. The size of the lens is the length and depth of the box containing the lens. The Horizontal length is now commonly referred to as the eye size when referring to the frame and lens size when referring to the lenses. Both are measured in millimeters. Size

9. They refer primarily to the horizontal measure of the lens, denoted by the letter “A”. The letter “B” denotes the vertical measure of the box enclosing the lens. The letter “C” refers to the width of the lens itself along the horizontal midline. Cont..

10. To measure the horizontal dimension of a frame, the measurement begins at the inside of the groove on one side and extends across the lens opening to the farthest part of the groove on the other. We cannot see the inside of the groove when looking from the front. This means we can estimate where it will be and hold the ruler so that the zero point is at the position of the left-hand side of the groove. Then we need to read the ruler at the position where the groove will be on the right. If the opening itself is measured, then about ½ mm per side needs to be added to the measure to allow for the depth of the groove. Horizontal Measure

11. Horizontal Measure

12. The effective diameter is found by doubling the distance from the geometric centre of the lens to the apex of the lens bevel farthest from it. Effective Diameter

13. The difference between the horizontal and the vertical measurements is known as frame difference and measured in millimeters. Frame difference is sometimes referred to as lens difference . Frame Difference

14. Frame Difference

15. The DBL is the distance between the two boxes when both lenses are boxed off in the frame. This distance is measured in millimeters. The DBL or bridge size is measured on the frame as the distance from the inside nasal eyewire grooves across the bridge area at its narrowest point. When measuring the bridge size, we cannot see the inside of the groove and must estimate its location. If the measurement is made from lens opening to lens opening, then approximately ½ mm per groove must be subtracted from the measure depending upon the depth of the groove. Distance Between Lenses (DBL) or Bridge size

16. DBL

17. The Distance Between the two geometric centers of the lens is known as the geometric center distance (GCD) OR The geometric center distance can be calculated by simply adding the eye size to the DBL . The result is the same . Geometric Centre Distance (GCD)

18. The GCD is also known by three other names : Distance between centers (DBC) Frames center distance Frame PD The term frame PD is commonly use in dispensing, but has no relationship to the wearer’s inner pupillary distance or distance between pupil centres . GCD

19. When specifying bifocal or trifocal segment height, the reference points are given in millimeters as either The distance below or above the horizontal midline.( called seg drop or seg raise) The distance from the lower line of the boxing system rectangle enclosing the lens shape (called seg height) Seg Height

20. Most temples are currently marked with the total, or overall temple length. Temple lengths are expressed in millimeters. Temple Length

21. The overall temple length is the distance from the center of the center barrel screw hole to the posterior end of the temple, measured along he center of the temple. Overall Temple Length

22. 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 length of drop. Length to Bend (LTB)

23. In this case the temple length could be specified as frame to bend (FTB) which would be slightly longer than LTB This measurement method is seldom used. Front to Bend (FTB)

24. Frame Markings

25. Most frames are marked according to the size with three measurements : eye size, DBL, and 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

26. When a frame marking such as 55 18 is seen, it means that the eye size is 55mm and the distance between lenses is 18mm The box – the eye size is measured according to the boxing method. The eye size and DBL are sometimes simply marked 55/18 or 55-18 The temple length is marked as 140mm Cont..

27. 1. ____ A a . 2 × (longest radius) 2. ____ B b . vertical boxing dimension 3 . ____ ED c. A + DBL 4 . ____ GCD d. eye size e. C Match the following

28. Q 1. A frame has the following dimensions: A = 51 B = 47 C = 49.5 DBL = 19 Seg drop (distance below the horizontal midline) = 4 mm What is the seg height? a. 19.5 mm b. 20 mm c. 21.5 mm d. 23.5 mm e. none of the above

29. Q 2 . The larger the frame difference, the __________ the lens shape. a. rounder b. more squared off c. narrower d. wider (i.e., deeper) Q 3 . If a frame’s dimensions are A = 50 and C = 48, with a frame difference of 8, what is B? a. 58 mm b. 56 mm c. 52 mm d. 46 mm e. 42 mm

30. Q5. What is the geometric center distance of a frame marked 5217? a. 52 b. 60.5 c. 69 d. 72 e. equal to the person’s PD

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