Measuring PD by yourself
Those who prefer to measure their PD independently will need a mirror and a millimeter ruler. Once you have the necessary tools, follow these steps:
- Stand in front of the mirror with approximately 8 inches between it and your face.
- Place the bottom edge of the ruler against your eyebrows.
- While holding the ruler in place, shut your right eye and line up the 0 mm mark of the ruler with the middle of your left pupil.
- Open your right eye and close your left eye while keeping a straightforward gaze.
- The number that aligns with the center of your right pupil reflects your binocular PD (more on this later).
Measuring PD with someone’s help
The steps for having a friend measure your pupillary distance are very similar to measuring it yourself. The main difference is that you’re relying on another person instead of a mirror. With a millimeter ruler and a trusted pal ready, follow these DIY measurement steps:
- Stand face-to-face with your friend, keeping approximately 8 inches between you.
- Stare straight ahead while you or your friend holds the top edge of the ruler across the bridge of your nose.
- Cover or close your left eye while your friend aligns the 0 mm mark of the ruler with the center of your right pupil.
- Cover or close your right eye and have your friend make note of which number aligns with the center of your left pupil.
- Repeat these steps a total of three times to ensure measurement accuracy.
It’s okay if you don’t get the same number for all three measurements. You can take the average number and use that as your measurement. Keep in mind that if one of the measurements is significantly different from the others, you should re-measure for accuracy.
Special apps are available that can help measure PD from home. However, the results may not be as accurate as when using a ruler or pupillometer.
What are the different types of PD measurements?
The different types of pupillary distance measurements are:
- Single PD, also called binocular PD
- Dual PD, also called monocular PD
- Distance PD
- Near PD
While all types measure pupillary distance, they do so in various ways.
Single PD (or binocular PD)
Single, or binocular, pupillary distance is the total distance from the center of your right pupil to the center of your left pupil. This is the standard measurement taken by most eye care practices and provides a single, two-digit number.
For adults, this measure is usually between 50 to 75 mm, with most adults measuring between 60 and 65 mm. Children have an average PD closer to 55 mm, and newborns around 40 mm.
Dual PD (or monocular PD)
Dual, or monocular, pupillary distance measures how far each pupil is from the bridge of the nose. Rather than having one large number, like 65 mm, dual PD gives you two smaller numbers, such as 32 mm and 33 mm.
Monocular PD is a more precise measurement than binocular PD because most faces are not symmetrical. The distance of the left pupil from the nose isn’t usually the same as the distance on the right side.
There are some instances where dual pupillary distance is required over single PD. These instances include:
Distance PD vs. near PD
Distance PD, also called far PD, is the distance between the pupils when the eyes are focused on a distant object. Near PD, or reading PD, measures the distance between the pupils when the eyes are focused on something up close.
Near PD is important for those who need prescription reading glasses. It’s also valuable for bifocals or progressive lenses that have a specific section of the lens for reading and nearwork.
Pupillometers have different settings to accommodate distance PD and near PD. When measuring distance PD, the patient is instructed to focus on an object approximately 20 feet away. To measure near pupillary distance, patients are told to focus on a point around 40 centimeters from them.
When the eyes focus on a close-up object, the pupils should move inward toward each other. This is a natural response known as the convergence-accommodation reflex.
What happens if my PD is wrong on my glasses?
If prescription lenses are produced with the wrong pupillary distance measurement, your pupils will not align with the optical centers of the lenses. While this isn’t necessarily dangerous, it can cause some uncomfortable symptoms, such as:
- Blurred or distorted vision
- Dizziness
- Headaches
- Eye strain
- Double vision
Having an accurate pupillary distance measurement ensures the clearest, most comfortable vision with your eyeglasses. If you suspect a problem with the pupillary distance in your lenses, an eye care professional can help.
Frequently asked questions about pupillary distance
While pupillary distance is a critical part of a vision prescription, not many people are familiar with its details. Below are common questions and answers regarding pupillary distance.
Is my PD number on my eye prescription?
Whether your PD is included on your eye prescription depends on your eye doctor. The United States has a rule, called the “Eyeglasses Rule,” that requires eye care professionals to share your vision prescription for free. However, this rule doesn’t include providing pupillary distance.
For this reason, pupillary distance is rarely included unless the patient requests it. There are a handful of states in which laws include PD in a prescription, such as:
- New Mexico
- Kansas
- Massachusetts
- Alaska
After updating your vision prescription with a comprehensive eye exam, remember to ask your eye doctor to add your pupillary distance.
What is a normal PD for adults?
Everyone’s eyes are different, including the pupillary distance. But there is an average range that eye doctors rely on when measuring PD. The average pupillary distances for various age groups are as follows:
- Children aged 5 to 9 – 55 mm
- Adolescents aged 10 to 19 – 60 mm
- Adults aged 19 and older – 60 to 65 mm
Does my pupillary distance change over time?
Pupillary distance changes throughout childhood because the skull and facial features grow during this time. Once you reach adulthood, pupillary distance usually stabilizes.
So, an adult’s PD measurement can be used from year to year, even if their vision prescription changes. An exception to this would be if the structure of an adult’s face changed due to reconstructive or cosmetic surgery. In this case, an updated PD measurement is recommended.
