Face Measurements
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Transcript Face Measurements
Face Measurements
R.D.Gopinath
Supervisor – Optical Sales
ARAVIND EYE CARE SYSTEM
A RAV I N D E YE H O S PI TAL
& Postgraduate Institute of Ophthalmology
Madurai, India
Why Measure PDs ?
Spectacle lens optical centres (OCs) should
correspond to the wearer’s PD
To avoid unwanted prismatic effect due to
decentration especially in higher Rx powers
Advanced lens designs must be positioned accurately
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Principles in Measuring PDs
PD rule (visual axes or pupil centres)
Pupillometer (visual axes)
Near centration distance
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PD Measurement devices
PD ruler.
Pupillometer
Pen torch
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How to do it…
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Binocular PDs
The variation between the visual axes and pupil
centres
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Binocular Distance PDs
Step 1
RE
0
PD Rule
Step2
LE
10 20 30
PD Rule
RE
0
10 20 30
40 50
Subject
Subject
Examiner
Examiner
RE
LE
A R A V I N D
E Y E
LE
C A R E
LE
62
RE
S Y S T E M
Why Monocular PD important?
Wearers’ faces are not always symmetric.
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PD rulers…
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Monocular PDs
PD Ruler Method
Sit directly opposite the patient (arm’s length)
Place ruler on the bridge of the patient’s nose
Hold pen torch under your left eye directed at
the patient’s RE
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Monocular PDs
Facial Fitting Principles PDs
Corneal reflex pupillometer (visual axes)
61mm
Monocular PD
Monocular PD
32mm
29mm
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The Pupillometer
Fast and accurate measurement for monocular and
binocular PDs
Practitioner’s
side
Binocular PD
Monocular PD
Subject’s
side
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Pupillometer
Ability to vary working distance from 20cm to infinity
Procedure:
Internal hairline moved until line and corneal reflection are coincident
Corneal reflection typically located nasal to pupil centre (2 to 5 )
Subject’s view
Practitioner’s view
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Direct Pupillary reflex marking
method
A pen torch will produce clear corneal reflections
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Facial Fitting Principles
PDs
Near centration distance
Near
Centration
Distance
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Binocular Near CDs
RE
LE
Subject
Spectacle Plane
Centre of nose
bridge to centre of
cornea
40c
m
Examiner
LE
A R A V I N D
E Y E
RE
C A R E
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Facial Fitting Principles
Centre of rotation to spectacle plane
27mm
Near centration
distance
The calculation
Near
Centration
Distance
Distance PD
Near CD = 400 X Distance PD
427
A R A V I N D
Working distance
400 mm
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Sources of error taking PDs with
the PD ruler
Parallax:
Practitioner does not close the non-observing eye
practitioner and patient are not directly in line
Incorrect ruler position: not straight or close enough
to the spectacle plane, especially at near
Significant differences in PDs of subject and examiner
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Aspherics and Near CD
Aberration or prismatic effect
The principal axis should pass through the eye’s centre of
rotation
For near, this requires a distance PD
Traditional setting for the OC for reading is the near CD
Eg. Rx = +6.00D both eyes Add = +1.00D both eyes
Readers set at distance PD = 2.8 base out
Readers set at near CD = 0
Prism at near with bifocals
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= 2.4 base out
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Face measurements
To select the appropriate size frame.
Temple length
Length of drop / Ear piece.
Bridge size.
Intra temporal distance.
Pantoscopic angle
Vertex distance
Segment height
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Summary
Frame & Face measurements are necessary to
Avoid unwanted prismatic effect.
Minimize the optical inherent defects.
Better reading area (in bifocal)
Correct fit on the face.
Accurate PAL dispensing.
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Thank You
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