Measuring the interpupillary distance binocularly and monocularly distance pds.Measuring near pd. Using three quater rule

1. Presenter- Ayush Duneja
B.Optom(1st Year)
Mentor- Mr. Mossab Sir
Measuring the Interpupillary
Distance
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2. Flow of Presentation
• Introduction
• Binocular PD
• Monocular PD
• PD measuring instrument
• Near PD
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3. Introduction
• The anatomic PD is the distance from the center
of one pupil to the center of the other pupil
• Measured in millimeters(mm).
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4. • Dispenser positions
at 40 cm (16 in)
• Dispenser closes
right eye
• Subject fixates on
dispenser’s left eye
• Dispenser lines up
zero point on
subject’s right eye at
the pupil center
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Steps in Measuring the Binocular
Distance PD

5. • Dispenser closes left eye, opens right eye;
subject
fixates right eye
• Dispenser reads off scale directly in line with left
pupil center
• Dispenser closes right eye, opens left; subject
fixates left eye
• Dispenser checks to make sure zero point is still
correct
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6. Common Difficulties and their solution
Problems Solutions
•Dispenser cannot close
one eye
•Occlude the eye with
free hand
•Subject is strabismic •Covers the subject’s
not been observed
•Subject is
uncooperative
child
•Take a canthus -
canthus measurement
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7. Other Measurements
• Canthus-Measuring from the outer canthus of
one
eye to the inner canthus of the other eye
• Limbus- Measuring from the outer limbus of one
eye to the inner limbus of the other eye
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Limbus
Canthus

8. Monocular PD
• Technique1(Using a ruler)
–Measure the binocular PD using center of the
pupil as the reference point
–Before moving the ruler, note the scale reading on
the ruler at the center of the nose. This is the right
monocular PD
– Subtract this reading from the binocular reading to
obtain the left monocular PD
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9. • Technique2(Using a frame)-
–Dispenser positions at 40 cm from the wearer and
at
the same level
–Dispenser opens left eye, closes right eye, and
instructs wearer to look at dispenser’s open
(left)eye
– Dispenser marks location of wearer’s right pupil
center and similarly marks center of left eye
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10. PD Measuring Instruments
• Pd ruler
• Essilor Pupillometer
• Topcon digital PD meter
• Cal coast PD meter
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11. Near PD
• Our eyes naturally converge when focusing on
something up close and measuring the PD while
in this converged position
• Required for single vision and multifocal lenses
• Can be either calculated or measured
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12. Steps in Measuring the Near PD
• Dispenser places his dominant
eye in front of subject’s nose at
the subject’s near working
distance
• Dispenser closes the other eye
• Subject fixates dispenser’s
open eye
• Dispenser places zero point of
PD rule at center of subject’s
right pupil
• Dispenser reads scale
marking at center of subject’s
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Subject
Dispenser

13. Calculating near PD
• Most commonly used is called 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
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14. References
• Text book of system of ophthalmic dispensing
• www.zennioptical.com
• www.allaboutvision.com
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