Progressive lens dispensing

Prepared by,
K.M.Manoj , B. Optom

 Distance from centre of the pupil to the centre
of the other pupil.
 Measured in millimeters ( mm )

•Failure to measure PD accurately, results in
misplacement of the optical centre of the lenses.
•Induces prismatic effect, requiring wearer to
turn eyes inward or outward to avoid diplopia.
•Overtime, this error causes visual discomfort
and Asthenopic symptoms.

 PD RULER
 PUPILLOMETER
 EYE PARTNER

 A: Between the center of the pupil
 B: Right Temporal pupillary margin to the Left
Nasal pupillary margin
 C: Right temporal limbus to Left nasal limbus

STEPS IN MEASURING BINOCULAR DISTANCE PD BY USING A
RULER
1.Dispencer Position at 40 cm ( 16 inches )
2.Dispencer closes right eye , patient fixes at dispencer open left eye
3.Dispencer lines up the ruler zero point on the subject’s right pupil, left
pupillary boarder or left limbus
4.Dispencer closes left eye , patients fixes at dispencer’s open right eye
5.Dispencer reads scale directly in line with subject’s left pupil center, left
pupillary boarder or left limbus
6.Dispencer closes right eye, opens left, subject fixates on dispencer’s left eye
7.Dispencer checks to make sure that zero point is still correct

PROBLEM SOLUTION
1. Dispencer cannot close one eye Occlude the eye with free hand
2. Subject is Strabismic Cover the subjects eye not been
observed
3. Subject is uncooperative child Take a canthus to canthus
measurement

STEPS IN MEASURING MONOCULAR DISTANCE PD BY USING PD
RULER
1.Measure the binocular PD using center of pupil as reference point
2.Before moving the ruler, note the reading at the centre of the nose. This is the
monocular PD of one eye
3.Subtract this reading from the binocular reading to obtain the reading of the
other eye

 Required for single vision reading glasses.
 Can be either measured or calculated.

STEPS IN MEASURING NEAR PD BY USING A RULER
1.Dispenser places his/her dominant eye in front of the subject’s nose at the
subject’s near working distance.
2.Dispencer close the non dominant eye.
3.Subject fixates on dispencer’s open eye.
4.Dispencer places zero point of the PD ruler at the center of the subjects’s right
pupil.
5.Scale reading at the center of the subjects’s left eye is read.

 Most commonly used is called the “ three –
quarter rule “
 It states that “ for every diopter of dioptric
demand, the optical center of each reading lens,
or the geometrical center of each bifocal
addition, should be insert 0.75 ( three quarters )
mm.”
 Dioptric demand = inverse of reading distance
in meters and is independent of actual bifocal
addition power.

 A spectacle lens wearer has the following Rx:
OD : - 1.00 DS
OS : - 1.00 DS
ADD : + 2.00 DS
Distance PD is 64 mm
What is the near PD at 40 cm ?

Dioptric Demand = 1/0.40 m = 2.50 D
Insert per Lens = 2.50 D × ( ¾ ) = 1.9 mm
= 2.00 mm ( approx )
We need to deduct 2mm from each lens , i.e 4mm
from the distance IPD.
Near IPD = 64 mm – 4 mm
= 60 mm

 Identification of Patient’s Requirements &
Expectations.

 FRAME SELECTION
Frame Shape
Frame Depth
Frame Size

 FRAME ADJUSTMENT
Adjust frame before taking facial
measurements.
Adjust when delivering spectacles also.

 Shorter
Reduced BVD gives wider field of view

 10 to 12 DEGREES
Increases Pantoscopic Tilt increases near field
of view.

 MEASURE MONOCULAR AND BINOCULAR
PD

 MARK PD ON FRAME AND DRAW
STRAIGHT LINE VERTICAL
 MAKE SURE THE PD IS COINCIDE WITH
THE VERTICAL LINE

 FITTING HEIGHT ( distance from pupillary
center to bottom of the lens )
Mark the line Horizontally
The fitting cross on progressive addition lens
must coincide with the pupil center of the
weares in their natural posture.

 The effective diameter of a lens is found by
doubling the distance from the geometric
centre of the lens to the apex of the lens bevel
farthest from it.
 This measurement helps to determine the
smallest lens blank from which the lens can be
cut.

 "A" Measurement - The horizontal distance between the
furthest temporal and nasal edges of the lens shape or the
distance between the vertical sides of the box. The A
measurement is also commonly known as the eyesize.
 "B" Measurement - The vertical distance between the
furthest top and bottom edges of the lens shape or the
distance between the horizontal sides of the box.
 Datum Line - The horizontal line that runs through the
vertical center of the frame.
 Geometric Center (GC) - The intersection of the Datum Line
and horizontal centers of each lens shape.
 Distance Between Lenses (DBL) - The shortest distance
between the nasal edges of each lens or the distance between
boxes. DBL is also commonly referred to as bridge size.

 Distance Between Centers (DBC) - The
horizontal distance between the geometric
centers of the lenses. DBC is also know as the
Geometric Center Distance (GCD), but more
commonly referred to as the frame PD. In
theory the DBC can be calculated by adding the
"A" Measurement to the DBL as marked on the
frame, however in practice the calculation may
differ from the actual measurement

 Seg Height - The vertical distance between the bottom edge
of the box and the top of the bifocal or trifocal segment
 Seg Drop - The vertical distance between the Datum line
and the top of the bifocal or trifocal segment Overall
 Temple Length (OTL) - The running distance between the
middle of the center barrel screw hole and the end of the
temple.
 Length to Bend (LTB) - The distance between the center of
the barrel and the middle of the temple bend.
 Front to Bend (FTB) - The distance between the plane of the
front of the frame and the temple bend. Used if there is a
significant distance between the frame front and the
beginning of the temple.

Progressive lens dispensing

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Progressive lens dispensing