FRAME MEASUREMENTSAND MARKINGS

OPTOM FASLU MUHAMMED

Familiarity with frame measurements and how they are marked is essential to proper ordering of prescription glasses.

DATUM SYSTEM

THE OLDER DATUM SYSTEM 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.

The datum system preceded the currently used boxing

THE BOXING SYSTEM

THE BOXING SYSTEM Geometric Center

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

Size The size of the lens then 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 the lens size when referring to the lenses. Both are measured in millimeters.

They are referring 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.

Horizontal measure of the lens

Effective Diameter

The effective diameter of a lens is found by doubling the distance from the geometric center of the lens to the apex of the lens bevel farthest from it.

Frame Difference

The difference between the horizontal and the vertical measurements is known as the frame difference and Is measured in millimeters.

Frame difference is sometimes referred to as lens difference.

Frame Difference

Distance Between Lenses (DBL) or Bridge Size The DBL is the distance between the two

boxes when both lenses are boxed off in the frame.

This distance is measured in millimeters.

DBL

Geometric Center Distance (GCD) The distance between the two geometric

centers of the lenses 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.

The GCD is also known by three other names:

1. Distance between centers (DBC)2. Frame center distance3. Frame PD The term frame PD is commonly

used in dispensing, but has no relationship to the wearer’s inter pupillary distance or distance between pupil centers.

Seg Height When specifying bifocal or trifocal segment

height, the reference points are given in millimeters as either

(l) The distance below or above the horizontal midline (called seg drop or seg raise)

(2) the distance from the lower line of the boxing system rectangle enclosing the lens shape (called seg height).

TEMPLE LENGTH

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

Overall Temple Length

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 the center of the temple.

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

Front to Bend (FTB)

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

FRAME MARKINGS

Most frames are marked according to 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.

Eye Size and DBL When a frame marking such as 50 □20 is

seen, it means that the eye size is 50 mm and the distance between lenses is 20 mm.

The box - the eye size is measured according to the boxing method.

The eye size and DBL are sometimes simply marked 50-20 or 50/20.

How to measure…….

Location of Markings

plastic frame Printed on the inside of the nose pad, or on

the upper outer section of the eye wire. Back side of the end piece, and the temple

must be folded closed to find it. On one end piece and the DBL on the other.

Metal framesEye size and DBL are usually on the inside of

the bridge or on the temples.

Frame Manufacturer Name, Color, and Country of Origin Frames should also be marked as to country

of origin, manufacturer, and frame name. Many frame manufacturers use a number rather than a name.

Consulting a frame reference catalog or database will help.

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.

Gold Classifications for Metal Frames With Substantial Gold Content Metal frames may not have any gold or any

significant amount of gold in the frame.

Gold or part-gold articles can be classified as fine gold, solid gold, gold filled, or having gold plating or gold flashing.

The karat system is used to determine the amount of gold present