To get the correct lens placement for your eyeglasses and lenses you must measure your pupillary distance. Pupillary Distance is the distance between the center of one pupil to the center of the other pupil, and it’s measured in millimeters. The PD is important; it helps the laboratory accurately create your eyeglasses by lining up your pupil with the center of the lens. The PD measurement technically is not part of the eye exam, but most eye care professionals will do it. Most opticians will measure your PD at no charge.
If you can not obtain the PD from your eye doctor or an optician, you can measure it yourself:
PD is the distance between the pupil centers (the central black dot of your eye).
The “limbus” is where the white part of the eye (sclera) meets the colored part (iris).
PD is measured in millimeters.
The PD can be measured by looking into the mirror or by someone helping you.
Illustration #1: Place the zero of the mm ruler at the inside limbus of one eye and measure at the outside limbus of the other eye. This illustration shows a PD measurement of 65 mm.
Illustration #2: Place the zero of the mm ruler at the center of the pupil of one eye and measure at the center of the pupil of the other eye. This illustration shows a PD measurement of 65 mm.
There are two options for taking your PD measurement; someone else can take your measurement or you can measure your own PD.
If someone else is taking this measurement, hold a millimeter ruler the zero at the limbus of the left eye and end the measurement at the limbus the right eye. After you have completed this measurement please note in millimeters your PD.
If you are taking your own measurement stand in front of a mirror at arm’s length away and measure from the limbus of your left eye to the limbus of your right eye using a millimeter ruler.
For accuracy, repeat the measurement three times. If the number obtained is different each time, take the average of the three for your PD.
If you are getting reading or computer eyewear glasses, simply take 3 mm off of the distance PD to account for convergence of the two eyes.
We were taught in school that taking the PD at the limbus is more accurate than trying to find the center of the pupil, especially on larger pupils, unless you have the more sophisticated instruments do it from the centers.
Some sites suggest that you take a standard 62 mm for adults or smaller for children if you can’t get the PD. We don’t’ recommend doing that, especially in higher powers. It can induce prismatic effect that can give you headaches and interfere with the balance of the muscles that move the eyes.
It’s highly recommended that you have an eye exam and ask for the PD to be put on your prescription.
Most eye care professionals and opticians (large chains) will do it for free.