Why Should You Care About Your PD Measurement?
What is a PD measurement and why does it matter to you? The pupillary distance measurement is a critical element in eye exams, but is not something every person thinks about unless they want to order glasses. That is when this elusive number becomes a vital statistic. Find out why PD measurements matter and how to find out yours.
What is a PD Measurement?
Tesco Opticians explains that the pupillary distance (PD) measurement determines the focal center of your eyeglasses. Put simply, this is the distance between the centers of your eyes. The measurement is taken in millimeters.
What is the Average PD Measurement?
Head size is a factor in pupillary distance, so measurement varies. Prescription Glasses Online states, for adults, the average ranges between 54 and 68 millimeters. For children, it is 41–55 millimeters.
How Do You Get a PD Measurement?
If you go to an optician for your glasses, you do not need to worry about your PD measurement. The optician will use one of three methods to determine PD as part of fitting you for new glasses.
- Manual method – The optician holds a PD stick, similar to a ruler, to your face and measures the distance between your pupils.
- Pupillometer – This is a device that measures both the distance between the pupils and pupil response.
- App – There are mobile and online applications that will measure pupillary distance using a webcam. The optician will have you stand on a mark in front of a computer and look at the screen. The software takes your picture and calculates the distance between your pupils.
What If You Order Glasses Online?
If you want to order glasses online after an eye exam, you need to provide your PD measurement. The doctor may be able to give you that information as part of the eye exam if you ask.
You can manually measure your pupillary distance, too.
- Stand in front of a mirror.
- Place a ruler with millimeter markings under your eyes, lying across the bridge of your nose. The zero mark should line up with the center of your right eye.
- Look directly into the mirror and mark the ruler at the center of the left eye. This marked place on the ruler is your PD measurement. For example, if the tick mark sits four lines after the 6 on the ruler, your measurement is 64 mm.
An accurate pupillary distance measurement is essential when ordering glasses after eye exams, especially if you need bifocals. Check with online glass retailers to see if they have a system to get the measurement using a webcam.