How to Measure Your Pupillary Distance

Pupillary distance, or PD, is the distance between the pupils (the pupils in your eyes; not the ones in your classroom). PD determines where we place the optical centres for your glasses. It is a crucial measurement. If it’s incorrect it can cause an optical prism, which unless prescribed, is a recipe for spectacles disaster. It can lead to blurry vision, eyestrain and headaches.



In my opinion, the best course of action is to have your local optician measure your interpupillary distance for you. A professional has the expertise and the tools, like a corneal reflex pupillometer. Try saying that five times fast. Not an option? Your second best bet is enlisting a friend to help. If all else fails you can try the least desirable option and do it yourself. Here’s the scoop on how to measure your pupillary distance:

  1. You will need a small ruler that measures in millimetres, known in the biz as a PD stick.
  2. Place the ruler along the bridge of your nose.
  3. Have your friend stand about arms length away from you.
  4. Make sure you are looking straight ahead and ask them to place the 1mm mark in the centre of your left eye.
  5. Finally, have your friend take note of the number that lines up with centre of your right eye.
  6. Be sure to repeat this process several times so you get it right.

If you currently have a pair of glasses, measuring your pupil distance will be a little easier. Simply have your friend use a felt tipped marker to place a dot at the centre of each pupil on your current lens. Then, use the handy PD stick to measure the distance between the two.

For a DIY method, preferably conducted as a last resort, hop on the selfie bandwagon. Take a picture of yourself holding the ruler on the bridge of your nose while looking straight ahead. Record the measurements as described above. You can also do this in a mirror, yet it is less likely to be accurate. Again, make sure to repeat the process several times.

The methods discussed determine the binocular PD, which is 100% acceptable within all of our standards. It’s just not infallible, as we divide the total by two. Therefore, a 62 PD is edged at 31 on the right and 31 on the left. Adults typically have a binocular PD within the 54-68mm range, while kids normally have a binocular PD within the 41-55mm range.

Ideally you’ll determine your monocular PD as well, which involves measuring from the centre of your bridge to the centre of the pupil. This is a more accurate measurement, since faces aren’t always symmetrical. A monocular PD is generally between 20-40mm. It’s difficult to conduct a monocular PD test yourself so we highly recommend having a trained professional measure your monocular PD for you.

Wondering where all of these numbers come into play on your prescription for eyeglasses or contacts? Well, you may notice columns labeled OD, OS and OU. OD is the abbreviation for the Latin term oculus dexter, meaning right eye, while OS, or oculus sinister, represents the left eye. OU, or oculus uterque, means both eyes.

The PD measurement is normally written beneath these other terms. For single vision lenses, a binocular PD measurement for both eyes (OU) may say 62, while the monocular PD for both eyes will read something like 31.5/34.5. The number on the left is for the left eye (OS) and the number on the right is for the right eye (OD). If you wear progressive or bifocal lenses, there will be a binocular PD listed for near and far distances for both eyes (OU). The near PD is calculated by subtracting 3mm from your distance PD measurement.

For a quick and exact pupillary distance measurement, visit the Spectacle Shoppe in Vancouver. Going it alone is a little like cutting your own hair. We’ll ensure your measurements are correct and your new glasses will offer you the truest vision.



Morgan Nahanee
Morgan Nahanee

Author

Morgan is The Spectacle Shoppe’s Lead Technician and Customer Relations Specialist as well as a Principle of Spectacle Shoppe. She is a licensed contact lens fitter and dispensing optician and has been working for The Spectacle Shoppe since 2006. She graduated from Douglas College’s two year Dispensing Optician and Contact Lens Fitting Program in 2008. From contact lens fitting to eyeglass repairs and adjustments Morgan is eager to help you with any optical needs. Connect with Morgan Nahanee on Google+