ARAVIND EYE CARE SYSTEM A R A V I N D E Y E H O S P I T A L & Postgraduate Institute of Ophthalmology Madurai, India ARAVIND EYE CARE SYSTEM A R A V I N D E Y E H O S P I T A L & Postgraduate Institute of Ophthalmology Madurai, India Face Measurements R.D.Gopinath Supervisor – Optical Sales

A R A V I N D E Y E C A R E S Y S T E M 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

A R A V I N D E Y E C A R E S Y S T E M Principles in Measuring PDs  PD rule (visual axes or pupil centres)  Pupillometer (visual axes)  Near centration distance

A R A V I N D E Y E C A R E S Y S T E M PD Measurement devices  PD ruler.  Pupillometer  Pen torch

A R A V I N D E Y E C A R E S Y S T E M How to do it…

A R A V I N D E Y E C A R E S Y S T E M Binocular PDs The variation between the visual axes and pupil centres 60 61

A R A V I N D E Y E C A R E S Y S T E M Step 1 Step2 Subject Examiner PD Rule Subject Examiner PD Rule RE LE RELE RE LE RE LE Binocular Distance PDs

A R A V I N D E Y E C A R E S Y S T E M 3134 Why Monocular PD important? Wearers’ faces are not always symmetric.

A R A V I N D E Y E C A R E S Y S T E M PD rulers…

A R A V I N D E Y E C A R E S Y S T E M 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

A R A V I N D E Y E C A R E S Y S T E M Monocular PD 29mm 32mm 61mm Monocular PDs  Facial Fitting Principles PDs  Corneal reflex pupillometer (visual axes)

A R A V I N D E Y E C A R E S Y S T E M Practitioner’s side Subject’s side Binocular PD Monocular PD Fast and accurate measurement for monocular and binocular PDs The Pupillometer

A R A V I N D E Y E C A R E S Y S T E M Subject’s view Practitioner’s view 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  )

A R A V I N D E Y E C A R E S Y S T E M A pen torch will produce clear corneal reflections Direct Pupillary reflex marking method

A R A V I N D E Y E C A R E S Y S T E M Near Centration Distance Facial Fitting Principles  PDs Near centration distance

A R A V I N D E Y E C A R E S Y S T E M RELE Centre of nose bridge to centre of cornea Spectacle Plane Subject Examiner LERE 40c m Binocular Near CDs

A R A V I N D E Y E C A R E S Y S T E M Near Centration Distance Distance PD Working distance 400 mm Centre of rotation to spectacle plane 27mm Near CD = 400 X Distance PD 427 Facial Fitting Principles  Near centration distance  The calculation

A R A V I N D E Y E C A R E S Y S T E M 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

A R A V I N D E Y E C A R E S Y S T E M 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 = 2.4  base out

A R A V I N D E Y E C A R E S Y S T E M 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

A R A V I N D E Y E C A R E S Y S T E M 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.

A R A V I N D E Y E C A R E S Y S T E M Thank You