What is your Pupillary Distance (PD)?
Pupillary distance (PD), is the distance between the center of one pupil to the center of the other pupil, measured in millimeters. This number is usually on your prescription given to you by your doctor, but if for some reason you don’t have it, it is easy to measure yourself.
This is important is because lenses are slightly curved, not flat. This is why your PD has to be properly measured so the eyeglass manufacturer knows how to align your prescription to your eyes.
People who have myopia, nearsightedness, should be particularly mindful because if their prescription lenses are not fitted properly to their PD, the person might experience “induced prism.” This is where the lenses will not focus light properly on the eyes and this can cause headaches and excessive eye strain.
Single PD OR Dual PD?
Single PD and dual PD are the two primary options for PD measurements.
Single PD, also known as binocular PD, is what most people talk about when PD is mentioned and this is the easiest version to measure yourself. This is the measure of the center of one pupil to the center of the other pupil (refer to the above section).
The other one, which is a little less common is dual PD or monocular PD. This is the measurement from your nose bridge to each eye. Dual PD is often believed to be the most accurate measurement of the two because many people’s nose-to-pupil measurement is not equidistant on both sides.
How do I measure PD?
- Grab a ruler that has measurements in millimeters. Grab a friend to help you out or do this in front of a mirror. Remove your glasses if you have any on.
- Close your right eye and align the ruler’s zero to the center of your left pupil.
- Open your right eye and close your left. Read the millimeter line that matches with the center of your right pupil with the other end of the ruler still centered on your left pupil.
- This number, the distance between your left pupil and your right pupil, is your pupillary distance.
How to Measure PD (With Glasses)?
- Make you are wearing your glasses and have a felt tip marker on hand. (You will be writing on your glasses, so you want to make sure the marker is washable).
- With your glasses on, stand still and focus on an object that is at least 20 feet away.
- Closing your left eye, mark your right lens directly over the object you are focusing on.
- Repeat step three, but this time do it with your right eye closed and mark your left lens.
- Once both lenses are marked, open both eyes to check that both dots overlap and form a single dot.
- Remove your lenses and measure the distance between the two dots with a millimeter ruler.
Note: If you have trouble viewing things up close, repeat the same steps except instead of focusing on an object that is 20 feet away, focus on something like a book/magazine or a computer screen.
What is a normal PD?
Once you measure your PD, you might be wondering what a normal range is. PD measurements can vary significantly. For an adult singular PD, the average range is between 54mm and 74mm.
Children are usually between 43mm and 54mm.
If you measured a PD number outside of this range, there is a possibility that this number is normal, but its best to measure one more time just in case!