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What is Pupil Distance (PD)? How to measure your Pupil Distance (PD)?

Pupillary Distance (PD) or interpupillary distance (IPD) is the distance (the industry standard is to measure in millimeters) between the centers of the pupils in each eye. This measurement is used when preparing to make prescription eyeglasses. Positioning lenses correctly in relation to the center of the pupils is especially important for higher-powered lenses due to the location of the optical center of the lenses. It can also be relevant to binoculars: they must be adjusted to suit the user's IPD, and the minimum allowed by some binoculars is still too great for people with a small IPD.


PD is measured either during the eye test or when prescription glasses are ordered. Obviously, we cannot measure your PD over the Internet, so it is best to make sure your PD is included in your glasses prescription.  

If your prescription does not contain your PD:

  • Ask to have it measured at an optical shop, some may charge a fee.
  • Contact an optical shop where you have previously purchased prescription glasses. Your PD has been measured if you have ever had prescription glasses made up.
  • Your previous optometrist may have a record of your PD.
  • Alternatively, try measuring your own Pupillary Distance as explained below. (Note: Measuring your own PD may not be as accurate as having a trained person do it. If your head or the ruler moves during the measurement then the reading will be inaccurate)

The higher the lens power in the glasses prescription, the more important it is to use an accurate PD. These procedures may not work for everyone. We recommend that you obtain a professional measurement of PD whenever possible.

if you have no Pupil distance data, we suggest you can measure it at an optical lab, that is very easy, it just several minutes can get it. 
if you want to measure your own PD, we also can guide you as below:

Measuring your own PD (Pupillary Distance):
(1) using the Mobil Phone App to measure your PD.  also will be fine. (recommended

Open your Mobil phone App Store, search " PDCHECK AR" And download this app. and then you can measure your PD with this App. notice. mounting TTL loupes need to fill near PD. So When you order, choose the PD with the same as the near PD you measured. 
(2) measure your PD with a ruler (not recommanded) , this method maybe not 


TIP: This should be done with glasses off, if the numbers on a ruler are difficult to see, then a magnifying mirror may help.

1. Whilst looking into a mirror hold a ruler against the bridge of the nose with one hand.

2. Close your left eye, and line the '0' up with the center of the pupil of your right eye as shown in the diagram.

3. Without moving your head or the ruler open the left eye and close the right eye. Read the number that lines up with the center of the pupil of the left eye. This number represents your Distance PD in millimeters. You have just used this technique to measure your distance PD.

4. Repeat this whole process at least 3 times to try and get a consistent measurement in millimeters. Make sure your head and the ruler do not move after lining up the zero on the ruler until you take the reading. This procedure may be difficult if one eye has very poor vision compared to the other eye.

how to get your near-pupil distance? the near PD is  normally less than 3mm or 4mm than PD
e.g. Distance PD = 60
        Near PD= 60 -3 = 57

Sometimes the center of the pupil is difficult to see. Instead of lining up the ruler with the center of the pupil, it is more precise to use the edge of the pupil as shown at the bottom of the page; (be careful to use the inside edge of one pupil and the outside edge of the other pupil.)


Getting a Friend to Measure Your PD:

This technique uses a second person to measure your Pupillary Distance (PD).

1. Both of you should be sitting down approximately 45cm apart. The person having their PD measured keeps both eyes open. When your friend is taking the measurement, they must keep one eye closed.

2. The ruler is held against the forehead as shown above. The person having the PD measured looks into the open eye of the person taking the measurement.

The s lined up with the center of one pupil. Record the number lining up with the center of the other pupil in millimeters. This is the measurement for the near PD,  Neither person should move their head during this procedure. This procedure will not work if the person having their PD measured has a turned eye. You have just used this technique to measure your near PD.

if you get your near pupil distance, the far distance is added  3 mm. (This rule is accurate for most people).

Eg Near PD= 57
Distance PD= 57 + 3= 60

Instead of using the center of the pupils, you can use the edge of the pupils as shown below. (be careful to use the inside edge of one pupil and the outside edge of the other pupil.)