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How to Measure Your Pupillary Distance (PD)

What Is Pupillary Distance and Why Is It Important

Pupillary distance (PD) is the distance between the centers of two pupils. This number is very important in most operations that require someone to wear eyeglasses or contact lenses. It helps determine where eyes should look at the moment.

A fitted pair of glasses will improve your sight and focus, relieve fatigue, and will make you happier about life in general. If your PD is incorrect, you may experience blurred vision, double vision, severe headaches, and even nausea.

Pupillary Distance Measurement

Even the smallest mistakes in pupillary distance measurement can give you mild headaches. Unfortunately, many people experience mild symptoms but never realize that an incorrect pupillary distance measure is the cause.

The Average Pupillary Distance

The average adult has a PD (pupillary distance) of almost 2.5 inches (54 - 75 mm). The average for children is 1.8 to 2.2 inches (43 - 58 mm).

Why Is Pupillary Distance Important?

A pupillary distance is crucial in determining the prescription for eyeglasses and contacts. Aligning the optical center of an eye exam translates to comfort and clear vision. If you don't need astigmatism correction and use low-power lenses, PD will probably be less of a problem.

However, for those who suffer from a high error category, especially if there is a need for astigmatism correction, PD measurement is critical. The farther you are from the center of your lenses, the more light is received by your eyes and the resulting retinal image becomes blurry.

What Determines Your Pupillary Distance?

PD measurement determines the shape of your glasses prescription. It identifies where one’s pupil size or shape best suits PD lenses too. Pupil size is defined by the distance between the two pupils.

What Is The Difference Between Single and Dual Pupillary Distance?

There is a single and a dual pupillary distance. Both are important when your optometrist is figuring out how your glasses should look. Single PD is the distance between the pupil and the bridge of your nose. You have to measure it when ordering progressive or multifocal glasses. On the other hand, dual PD is the distance between the center of the pupil of the right eye and the center of the pupil in the left eye.

How To Measure Pupillary Distance (PD)

Most people’s pupillary distance is measured when they visit their eye doctor and get fitted for a new pair of prescription glasses. These measurements are also carryable over to either contacts or sunglasses. However, do you know that it's also possible to measure PD without even leaving home?

You can do this measurement at home with different methods. You can apply the first method by following these steps:

  • First, stand 8 inches from a mirror with your eyes open. Hold a millimeter ruler against your brow bone while you are standing in this position.
  • Close your right eye and line up the 0 mm mark on the ruler with the center of your left eyeball.
  • Looking at yourself in the mirror straight on, shut your left eye and then open just your right eye.
  • Find the millimeter line that is exactly in the middle of your right pupil and write down what it says. It is your PD measurement.

There is another method for measuring PD if you already wear eyeglasses. You’ll need a non-permanent pen.

  • With your glasses on, stand about 12 inches from a bathroom mirror and stare at yourself in the reflection.
  • Close your right eye and place a small mark on the left lens of your glasses in front of your pupil.
  • Holding your head still, close your left eye and open your right eye for a minute.
  • Standing in front of the mirror, look into your eyes, and place a small mark on your right lens.
  • Remove your glasses and hold the ruler between two dots. It is your PD measurement.

Another option is to download a free app! For example, GlassesOn is an app available for both iOS and Android devices. This app measures PD for you using computer vision.

You can also compare your measurements to the prescription that's provided to you by your healthcare provider or if you have a medical history.

Talk to your doctor if you believe your PD was measured inaccurately when you were fitted for eyeglasses or if you don’t think your glasses fit correctly.

How to Find Pupillary Distance on Prescription

If you have a pair of eyeglasses, check for your pupillary distance on the prescription. It will be a number followed by a “PD.” Prescriptions for contact lenses will likely not have a box for pupillary distance. You can ask your eye doctor about this if you don’t know where to find your PD.

Effects of Pupillary Distance on Eyeglass Frame Size

PD affects the size of your glasses' frames but not the shape. This is because it does not influence the shape and size of your lenses. Frame measurements are sometimes overlooked when prescription eyeglasses are being produced.

The size of a frame affects the PD because the location of the optical center is based on the size of a frame. If you prefer large lenses and frames this is especially true.

Finding the perfect set of prescription frames for your eyes needs to be just as important as getting an accurate PD measurement. Improperly fitted glasses can cause headaches and other side effects associated with your vision by putting unnecessary pressure on your forehead.

Your ophthalmologist will retrace the measurements of your glasses or check the fit to see if there's a problem.

Your eye doctor or optician can help determine the right frames for you. If you order glasses online, you can use an old pair of properly fitted glasses as a template.

An accurate PD measurement helps your eyes live a life that's as close to normal as possible. It drastically enhances the overall quality of vision as well as allows your eyes to focus correctly and work as they should.

Your PD number or pupillary distance is an essential step when it comes to purchasing glasses online. It helps you pick the right product for your face and protects your eyesight while wearing them.

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