The document discusses various optical frame measurement terms and systems. It defines key terms like eye size, bridge size, geometric center distance, temple length, and segment height. It explains that eye size is measured as the horizontal width of the lens opening or "box" and bridge size is the distance between the two boxes. The geometric center distance is calculated by adding the eye size to the bridge size. Segment height is measured in millimeters from the horizontal midline or lower box line.

1. 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.
 Horizontal lines were drawn at the highest
and lowest edges of the lens

5.  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.

7.  A horizontal line halfway between the top
and bottom of the lens.
 In the boxing system, this line is more
commonly referred to as the horizontal
midline or the 180degree line.

8.  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.

9.  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.

10.  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.

11.  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.

13.  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.

14.  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.

16.  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.

18.  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 .

19.  The GCD is also known by three other names
:
1) Distance between centers (DBC)
2) Frames center distance
3) 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.

20.  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)

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

22.  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.

23.  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.

24.  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.

26.  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.

27.  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

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

29. 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

30. Q 2. The larger the frame difference, the __________ the
lens shape.
 a. rounder
 b. more squared off
 c. narrower
 d. wider (i.e., deeper)
Q3. 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

31. 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

32.  THANKYOU