Measuring interpupillary distance
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This document discusses measuring interpupillary distance (IPD). It begins by defining IPD as the distance between the centers of the two pupils. It then lists several instruments that can be used to measure IPD, including rulers, gauges, and digital meters. The document provides techniques for measuring both binocular and monocular IPD using a ruler. It also discusses measuring near IPD, either directly or by calculating it using the three-quarter rule based on dioptric demand and distance PD. An example calculation of near IPD is shown.
Measuring interpupillary distance
- 1. Measuring Interpupillary Distance Indra Prasad Sharma Optometrist, ERRH Mongar
- 2. Anatomic pupillary distance Distance from centre of one pupil to the centre of the other pupil Measured in millimeters(mm) Sharma IP,
- 3. Sharma IP, Why to measure IPD?
- 4. Instruments for measuring PD PD ruler Rodenstock Interpupillary gauge Pupillometer (Elissor pupillometer) Topcon Digital PD meter, Model PD 5 Cal coast PD ruler Sharma IP,
- 5. Instruments for measuring PD Cal coast PD Meter Digital Essilor Pupillometer Sharma IP, PD ruler
- 6. We can use this Sharma IP,
- 7. Binocular Distance IPD Sharma IP,
- 8. Sharma IP, A: Between center of two pupil B: Right temporal pupillary margin to left nasal pupillary margin C:Right temporal limbus to left nasal limbus
- 9. Technique Steps in Measuring binocular distance PD using a ruler 1.Dispenser position at 40 cm(16 inches) 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 Sharma IP,
- 10. Common difficulties and their solution Sharma IP, 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
- 11. Sharma IP, Monocular Distance IPD
- 12. Technique Steps in Measuring 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 one eye 3.Stbtract this reading from the binocular reading to obtain the reading of the other eye. Sharma IP,
- 13. Near PD Sharma IP,
- 14. Near PD Required for single vision reading glasses or for multifocal lenses Can be either measured or calculated Sharma IP,
- 15. Technique Steps in Measuring 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. Sharma IP,
- 16. 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 Sharma IP,
- 17. Example A spectacle 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? Sharma IP,
- 18. Solution: 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 Sharma IP,
- 19. Orthoptics as a career (ZG)