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Pupillary Distance (PD) is the distance (usually measured in millimeters) between the centers of the pupils in each eye. This measurement is used when making prescription eyeglasses. Positioning lenses correctly in relation to the pupil centers is especially important for higher powered lenses. This measurement is usually taken twice: 1st with the patient focusing at a distance, and 2nd at near focus. The 2nd measurement is used for reading glasses, and bifocals. The measurements may also be verified with a pupilometer, since most practicioners take preliminary measurements with a millimeter ruler placed across the bridge of the nose.
- The typical pupillary distance for adults is around 54-68 mm, while measurements generally fall between 48 and 73 mm.
- For children the measurement usually ranges from 41 to 55 mm.
An optician can accurately measure your PD, or you can measure it yourself using a ruler, with someone’s assistance or a mirror.
An optometrist will typically measure the distance from one eye's nasal limbus to the other eye's temporal limbus, as the actual centre of the pupil can be very difficult to locate. In very young children and babies, where the patient is unlikely to stay still, the optician will typically measure from one medial canthus to the other lateral canthus. In this case, measurements are often inaccurate by a few millimetres.
See also
External links
- Diagram at eyeglassdirect.com
- PD measurement Method and Procedure
- Measuring your own PD at Vita Optical
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- This page was last modified on 24 July 2008, at 22:39.
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