When ordering your glasses online you may have reached the point where you are asked for your PD measurement - but what exactly are we asking for?
Your PD (Pupillary Distance) is the measurement (in millimetres) between the centre of your pupils, which is usually taken by a professional so that your new lenses can be made with the correct optical centres.
The average binocular distance PD for females is usually around 61mm whilst the average for a male is 64mm. However, you may find that your PD is higher or lower than the average depending on your features and size. Also, as a rule of thumb, your PD will be around 1.5mm lower for viewing close objects so for reading glasses, you would have a smaller PD than for distance glasses.
For varifocals, we order the glasses based on your distance PD and this is automatically adjusted for the reading portion of your lenses. Often, you might see two measurements are required for your PD. This is known as your monocular PD and is the measurement from the centre of the bridge of your nose, to each pupil individually. Usually, it is half of your distance (or binocular) PD, but again this can vary from person to person.
What happens if I am not looking through the optical centres?
If your lenses are not centred to your individual PD measurement several things could happen, and the severity of symptoms really depends on your prescription and how far off the PD measurement is. If you are looking through a point other than the optical centre of your lenses you may not be getting the best vision possible from your glasses. This can lead to eye strain, headaches or even images appearing to be displaced (prismatic effect). The higher your prescription, the more noticeable this effect as your eyes are naturally attracted to looking through the correct optical centre of the lenses.
How do I get my PD?
Your PD measurement is usually taken during the dispensing process after your eye test so it may not be written on your prescription. You can request this information from your optician (but there will likely be a charge to provide it). SureSpecs are able to make your glasses by using an average PD or if you have a high prescription and want to have your PD professionally measured, you can book an appointment for a SureSpecs Dispensing Technician to visit you at a convenient time and location to take the measurement for you*.
*Mainland UK only. £30 charge or complimentary with varifocal orders over £199.