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IPD Measurement
The document discusses measuring interpupillary distance, which is the distance between the centers of the two pupils, and describes various instruments that can be used to measure IPD at both distance and near. It provides steps for measuring binocular distance IPD, monocular distance IPD, and near IPD using a ruler, and includes an example of calculating near IPD using the three-quarter rule based on dioptric demand.
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IPD Measurement
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- 2. Anatomic pupillary distance Distancefrom centre of one pupil to the centre of the other pupil Measured in millimeters(mm) Sharma IP,
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- 4. Instruments for measuringPD SharmaIP, P D ruler Rodenstock Interpupillary gauge Pupillometer (Elissor pupillometer) Topcon Digital PD meter, Model PD 5 C a l coast PD ruler
- 5. Instruments for measuringPD Calcoast PD Meter Digital Essilor Pupillometer PD ruler Sharma IP,
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- 8. A :Between center of two pupil B : Right temporal pupillary margin to left nasal pupillary margin C:Right temporal limbus to left nasal limbus Sharma IP,
- 9. Technique Sharma IP, Steps inMeasuring binocular distance PD using a ruler 1.Dispenser position at 40 cm(16inches) 2.Dispenser closes right eye , patient fixes at dispensers open left eye 3.Dispenser lines up the ruler zero point on the subject’s right pupil, left pupillary border or left limbus. 4. Dispenser closes left eye , patient fixes at dispensers open right eye 5.Dispenser reads scale directly in line with subject’s left pupil center ,left pupillary border or left limbus 6.Dispenser closes right eye, opens left; subject fixates on dispenser’s left eye 7.Dispenser checks to make sure that zero point is still correct
- 10. Common difficulties andtheir solution SharmaIP, Problem Solution 1.Dispenser 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- canthus measurement
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- 12. Technique Sharma IP, Steps inMeasuring monocular distance PD using a ruler 1.Measure the binocular PD using center of pupil as reference point 2.Before moving the ruler, note the reading at the center of the nose. This is the monocular PD of oneeye 3.Stbtract this reading from the binocular reading to obtain the reading of the other eye.
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- 14. Near PD Sharma IP, Required for single vision reading glasses or for multifocal lenses C a n be either measured or calculated
- 15. Technique Sharma IP, Steps inMeasuring near PD using a ruler 1.Dispenser places his/her dominant eye in front of the subject’s nose at the subjects near working distance 2.Dispenser close the non-dominant eye 3.Subject fixates on dispenser’s open eye. 4.Dispenser places zero point of the PD ruler at the center of subject’s right pupil. 5.Scale reading at the center of the subject’s left eye is read.
- 16. Calculating near PD SharmaIP, M o s t commonly usedis called three -quarter rule I t 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
- 17. Example Sharma IP, Aspectacle lens wearer has the following prescription: OD: -1.00 DS OS: -1.00 DS Add: +2.00DS Distance PD is 64mm. What is the near PD at 40 cm?
- 18. Solution: Sharma IP, Dioptric demand=1/0.40=2.50 D Insert per lens =2.50 x (3/4) =1.9mm = 2.00mm (approx) We need to deduct 2 mm from each lens i.e 4 mm from the distance IPD Near IPD= 64mm- 64 mm =60mm Easiest Solution: Deduct 4 mm from distance PD for normal working distance
- 19. Orthoptics as acareer (ZG)