Pupillary distance explained: how to measure PD

Having your eyes tested is the first step to getting a prescription. There are a number of elements that are necessary for your prescription. It is especially the numbers indicated on it that are important.

The numbers are necessary to provide you with the correct prescription eyeglasses. This will also be helpful when you need prescription sunglasses. It is also important to be able to read your own prescription.

Most optometrists have the necessary tools and equipment to do your eye test for you as accurately as possible. They have the equipment to photograph the back of your eyes, test for eye pressure, and see if you have any defects such as cataracts. If there are any medical issues with your eyes that eyeglasses cannot solve, they will refer you to an ophthalmologist.

However, an eye test is important to find the prescription for your left and right eyes. Each eye will have a number indicating how weak it is separately. It will show how the lens will refract the light, a correction number for astigmatism, and the diopters, which are the measurement units for the optical power of your lens. Included are also the correction numbers for close focusing.

All of these numbers are extremely important when you need to get your prescription from Lensmart and should be as accurate as possible. Unfortunately, these numbers will be meaningless if you do not have an accurate measurement for your pupillary distance (PD).

What is Pupillary Distance?

Pupillary Distance (PD) is the distance, in millimeters, between the center of one pupil to the center of the other. The PD is needed to manufacture your glasses because it determines the exact optical center of the lens, which is the point where you look through the lens.

The optometrist is able to provide you with a more accurate PD as they can measure the distance according to your needs. This means that they will measure either the far pupillary distance or the near pupillary distance. This will depend on the type of eyeglasses you need. And you can measure your own PD at home as well, which does not necessarily need to be on your prescription. 

How to Measure your Pupillary Distance?

Millimeter measurements are the most accurate for measuring PD. To get the most accurate PD measurement, you can visit your optometrist to get it added to your prescription if you are going to order your prescription online. However, for this purpose, you can also do it yourself at home.

Recommend to use a physical PD ruler or consult your ophthalmologist.

Steps to measure PD:

1. Position yourself arm's length from your friend or yourself approximately 8 inches (20cm) away from a mirror. 

2. Close your right eye and align the 0mm over the center of your left pupil.

3. Close your left eye and note the reading directly over your right pupil. That will be your Total PD.

You can download PDF version of Lensmart's PD measurement guide here and print it to A4.

The Importance of Pupillary Distance

All the numbers on your eye prescription are important. However, in order to get your prescription to "read" exactly, you need to have the correct pupillary distance for your eyes. It need not be one hundred percent accurate, but it needs to be as accurate as possible to get the right-sized glasses, such as Jasmine or Jini as below.

Although it's not frequently necessary for managing your vision treatment, your eye doctor may use PD to examine specific aspects of your eye function or vision. Because of this, even if you require it when ordering glasses, it is not always on your prescription. It does, however, make it most helpful when ordering your eyeglasses, if the optometrist can add it to your prescription.

Furthermore, if you have the most accurate PD, you can be assured that your prescription glasses will not blur and give you headaches. It will help you get the right prescription that will improve your vision, not make it worse.

The Average Pupillary Distance for Men and Women

As noted before, getting your pupillary distance is important to get your eyeglass prescription as accurately as possible. This also means that you or your optometrist have to take into consideration that there are slight differences in the PD of men and women.

For the most part, the average PD for adults in general, including both males and females, is 63 mm. It can be as low as 50 mm, though, and as high as 70 mm. However, according to research, there is a difference in the average measurements between males and females.

Females have a pupillary distance between 53 and 65 mm on average. This is why it is important to have the actual measurement of your own eyes. It will give you accurate prescription eyeglasses and improve your vision.

The importance of the most accurate PD measurement applies to men as well. Males, on the other hand, have a pupillary distance between 55 and 70 mm. It is therefore important to get as exact a measurement as possible for men as well.

These are generally the ranges of PD for men and women. Because it is an estimation, each individual needs to have their own specific measurements to get it as accurate as possible.

Frequently Asked Questions About Pupillary Distance (PD)

Q1: Is my PD always the same, or does it change?

Your PD generally remains stable once you reach adulthood. However, for children, PD can change as they grow. This is why it's crucial for children's PD to be measured by an eye care professional.

Q2: What happens if my PD is wrong on my glasses?

If your PD is incorrect, the optical center of your lenses won't align properly with your pupils. This can lead to various discomforts like blurred vision, eyestrain, headaches, and even a "prism effect" which makes it feel like objects are displaced.

Q3: My eye doctor didn't put my PD on my prescription. Can I still get it?

Yes! Optometrists often don't include PD on prescriptions as it's not always medically necessary for vision treatment. However, you can always ask your eye doctor to provide your PD measurement separately.

Q4: How can I measure my PD if I don't have a ruler?

You can use smartphone apps or download and print a printable PD ruler. Another way is to have a friend help you by marking the distance between your pupils on a piece of paper or a card.

Q5: Do I need a different PD for reading glasses versus distance glasses?

Potentially, yes. Your far pupillary distance (for distance vision) is usually slightly larger than your near pupillary distance (for reading or computer work). This is because your eyes naturally converge a few millimeters when focusing on close-up objects. Many online retailers will use your single PD for all purposes, but for specific needs like dedicated reading glasses, a near PD measurement might be more accurate.

Q6: What's the difference between 'single PD' (or 'total PD') and 'dual PD' (or 'monocular PD')?

Single PD is one number for the total distance between your pupils (e.g., 63mm). Dual PD uses two numbers, measuring from the center of your nose to each pupil separately (e.g., Right: 31.5mm, Left: 31.5mm). Dual PD offers greater precision, especially for complex prescriptions or progressive lenses. To learn more about when to use single or dual PD, check out our blog post, " difference between ‘single’ and ‘dual’ pupillary distance".

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