PD or Pupilary Distance is a term used in optical world and you can hear about it at your doctor or even at the optical store. But much details about this PD is not abundantly available to everyone. Many people, even those who have worn glasses for decades do not know what this term stands for. Pupilary distance is an important part of the Eye prescription, especially if you’re planning to order your new glasses online.
PD distance is the distance between the midpoint of the two pupils. While the lenses are prepared it’s cruicial to position optical lenses correctly in relation to the pupils of the wearer for high powered lenses because the optical center of the lenses can be aligned properly. Knowing this value creates optical lenses with zero errors and gives best vision. So it’s important to know the PD value and your optometrist will know how to determine it.
PD distance is different for each individual but for most adults, this value ranges between 54 to 68mm. Children typically have a PD value between 41 to 55 mm. The PD distance can be measured in two ways. The first is called binocular PD Distance calculation, which is a pupil-to-pupil measurement. In this type of measurement, the values would be between 41-80 mm. The second type of measurement is called monocular PD Distance measurement, which is a per-eye measurement from the pupil to the middle of the face. In this type of measurement, the values would be between 20-40 mm. Monocular measurements are most often used when the intended wearer’s face is not perfectly symmetrical. In this case one eye can be closer or farther from the middle of the face than the other.
PD is usually measured by your eye doctor while you’re getting your eyes examined. If your doctor does not measure your PD during your eye exam, or if it’s missing from your prescription, you can request a PD measurement. Some eyecare doctors may charge extra for a PD measurement, but most doctors will include it as part of the eye exam and write the value down in your prescription.
If you’re ordering online, you must know your prescription details and values beforehand. Even if you’re getting it done at a store, this value is important to make your lenses perfect. The details you enter are important, and it’s essential that you know the values well. In this regard it’s best to consult with your doctor and tell him to mention the values in the prescription properly.
A spectacle lens made with correct PD values will have the optical centres rightly aligned with your pupils for the best vision. So get your PD measured and mention it the next time you’re getting your spectacles done for the best fit online .