This document discusses measuring monocular and binocular pupil distance (IPD) using various methods. It describes steps for measuring binocular IPD using a ruler as well as monocular IPDs. Common difficulties in measuring IPD and their solutions are outlined. The importance of accurately measuring IPD is discussed as improper measurement can induce prismatic effects and visual discomfort. A formula for calculating near IPD from distance IPD and dioptric demand is also provided.

1. MONOCULAR AND BINOCULAR
IPD MEASUREMENT
VINIT KUMAR & RAY ARBIND
OPTOMETRIST

2. PD/IPD ? IPD

3. IMPORTANCE OF IPD
> Failure to measure PD accurately ,results in misplacement
of optical center of the lenses,
Induces prismatic effect, requiring wearer to turn eyes
inward or outward to avoid diplopia
 overtime ,this error causes visual discomfort and
asthenopia

4. HOW TO MEASURE PD
•Ruler and torch
•Pupilometer
•Autorefractometer
•Automated keratometer

5. STEPS IN MEASURING THE
BINOCULAR DISTANCE PD
• 1. Dispenser positions at 40 cm (16 in).
2. Dispenser closes right eye, subject fixates on dispenser’s left eye.
3. Dispenser lines up zero point on subject’s right eye at the pupil
center, left pupillary border, or left limbus.
4. Dispenser closes left eye, opens right eye; subject fixates right eye.
5. Dispenser reads off scale directly in line with left pupil center, left
pupillary border, or left limbus.
6. Dispenser closes right eye, opens left; subject fixates left eye. 7.
Dispenser checks to make sure zero point is still correct

6. PROCEDURE

7. STEPS IN MEASURING MONOCULAR PDS
USING A RULER
1. Measure the binocular PD Using the center of the pupil as the
reference point.
2. Before moving the ruler, note the scale reading on the ruler at the
center of the nose. This is the right monocular PD.
3. Subtract this reading from the binocular reading to obtain the left
monocular PD.
For example, the binocular PD is 66. The scale reading at the center of
the nose is 32. The monocular PD for the right eye is then 32. To
calculate the monocular PD for the left eye, subtract 32 from 66, to get a
reading of 34

8. STEPS IN MEASURING MONOCULAR PDS USING THE SAMPLE
FRAME
• 1. The selected frame is adjusted in exactly the same manner as it will be when
worn. 2. Dispenser positions at 40 cm from the wearer and at the same level.
3. Dispenser opens left eye, closes right eye, and instructs wearer to look at
dispenser’s open (left) eye.
4. Dispenser marks location of wearer’s right pupil center on glazed lens.
5. Dispenser opens right eye, closes left eye, and instructs wearer to look at
dispenser’s open (right) eye.
6. Dispenser marks location of wearer’s left pupil center on glazed lens.
7. Dispenser rechecks the locations of the marked crosses by repeating steps 3 and 5
and notes the positions of the marked crosses.
8. If one or both crosses are wrong, the frames are removed and the cross(es) erased
using a damp cloth.
9. When crosses are accurate, monocular PDs are measured from frame center to

9. PROCEDURE

10. STEPS IN MEASURING THE NEAR PD
• 1. Dispenser places his or her dominant eye in front of
subject’s nose at the subject’s near working distance. This is
the distance for which the near prescription is intended—
normally 40 cm (16 in).
2. Dispenser closes the nondominant eye.
3. Subject fixates dispenser’s open eye.
4. Dispenser places zero point of PD rule at center of subject’s
right pupil. 5. Dispenser reads scale
marking at center of subject’s left pupil.

11. IPD MEASURE WITH PUPILLOMETER
• The dispenser asks the subject to hold his or her end of the pupillometer so that
the pads rest on the nose .
• The forehead support should be against the forehead.
• The dispenser uses one eye to look into the instrument.
• An internal light produces an image by reflection on each cornea, and the hairline
within the device is moved until coincident with this corneal reflection .
• The measurement is assumed to correspond with the subject’s line of sight, but is
an objective measurement of the position of the corneal reflection rather than the
position of the line of sight.
• In addition to a distance PD, near PD may be measured for near points from 30 or
35 cms to infinity.

12. PROCEDURE

13. COMMON DIFFICULTIES AND THEIR
SOLUTION
PROBLEM SOLUTION
Dispenser cannot close one eye Occlude the eye with free eye
Subject is strabismic Cover the subjects eye not been observed
Subject is uncooperative chid Take a canthus – canthus measurement

14. CALCULATING NEAR PD
1.Most commonly used is called “three quarter rule”
2.It states that “for every dioptre 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”.
3 .Dioptric demand =inverse of reading distance in meters
and is independent of actual bifocal addition power

15. COMMON CAUSES OF ERRORS
1. There will be an error in measurement if the measurer’s PD differs significantly
from the subject’s because the lines of sight are not parallel. For example, if the
measurer’s PD is 16 mm larger than the subject’s, the reading will be 1 mm too
high because of this parallactic error.
2. The above error will be increased if the PD rule is not tilted on the subject’s nose
so that the scale is in the most recessed area. The most recessed area corresponds to
the approximate position where the spectacles will be worn.
3. Just as error will be increased when the measurer’s PD is signifi cantly different
from the subject’s, the parallactic error will also be increased even more if the
dispenser is too close to the subject. Too close is closer than the normal 40 cm (16
inch) distance.

16. ERRORS
4. A significant error will be induced if the subject is strabismic (one eye
turns in or out) or if the subject does not fixate binocularly* during the
PD measurement.
5. An error can result if the subject’s head moves.
6. An error can result if the person measuring moves his or her head.
7. An error will result if the person measuring does not close or occlude
one eye at a time to ensure sighting from directly in front of the subject’s
eye under observation.
8. The subject may not look directly at the measurer’s pupil during the
test, as he or she should, which will result in an error.

17. EXAMPLE
Q.A spectacle lens wearer has the following prescription
R: −1.00 D sphere L: −1.00 D sphere add: +2.00
.The distance PD is measured as 64 mm. For a 40 cm
working distance, what is the expected near PD?

18. SOLUTION
• Dioptric demand =1/0.40=2.50D
• Insert per lens=2.50x0.75=1.9mm(2.00mm)
• So we need to deduct 2mm from each lens i.e 4 mm
from distance IPD.
• Near IPD =64-4=60mm

19. IMPORTANT QUESTIONS
Q. Define IPD .write about different method of measuring IPD?
Q.Write about difficulties of measuring IPD with their solution.
Q. Q.A spectacle lens wearer has the following prescription
R: −1.50 D sphere L: −2.00 D sphere add: +3.00 .The
distance PD is measured as 64 mm. For a 25 cm working
distance, what is the expected near PD?