What is Pupillary Distance and What is its Significance?

Have you ever felt intimidated by the optical industry jargon shot by your optician during an appointment? One of those terms is Pupillary Distance. Read through this article to know what it exactly means and how it’s related to your glasses and sunglasses.

What is Pupillary distance?

Pupillary Distance is the distance measured between the centers of our two eye pupils. Pupil is the black coloured circular center of our eye that lets through light. It increases or decreases in size according to the amount of light needed.

Single Vs. Dual PD

• Monocular PD

Single or monocular PD is measured from the center of the pupil of one eye to the bridge of your nose.

• Binocular PD

Dual or binocular PD is measured from the center of the pupil of one eye to the centre of the pupil of the other eye. It is also referred to as interpupillary distance.

• Which one is more accurate?

For most of us, our eyes are not located symmetrically on our face. Measuring the dual PD can make a frame with inaccurate lens dimensions for the eye. For example, if your binocular PD is 60 mm, your monocular PD can not necessarily be 30–30 mm, but for an asymmetrical face, they can be 28 mm and 32 mm. Therefore, monocular PD should be used for a more accurate measurement. However, the binocular PD is used more generally for standard size of frames.

How is it useful?

The pupillary distance measurement is used when you go to an optician to buy glasses. Every eye lens has an optical centre which is determined with the help of your PD. If you look at your lenses, you’ll notice that they are not a flat piece of transparent glasses but slightly curved from the centre. The PD is used to align the eye lens with your eye and determine the spot where you look through your glasses.

Kids and Adult PD

• For kids, the pupillary distance can lie anywhere between 43–58 mm.
• The average pupillary distance of an adult human can be about 63 millimeter.
• For an adult woman, the PD can range between 51 mm and 74.5 mm, while for an adult male, the PD ranges from 53 mm to 77 mm.

How to measure your own PD?

When you are looking to buy prescription or reading glasses online, you’ll need to know your PD to purchase the right pair of glasses. Here is how you can do that:

Do it yourself

• Stand 8 inches away in front of a mirror and hold your face straight.
• Place a ruler on your forehead, against the brows, with the millimeter scale facing your eyes.
• Close your left eye and place the zero above the centre of your right pupil.
• Now, open your left eye and close your right eye.
• Take the measurement from the centre of your right pupil to the bridge of your nose. This is your monocular/single PD.
• Repeat the process for the other eye — close your right eye, place the zero above the centre of the left eye and then take the measurement from the centre of the left pupil to the bridge of your nose.
• For binocular/dual PD, close the left eye, place the zero above the pupil centre of the right eye, open left eye and close the right eye. Now, with your left eye open, measure the distance between your two pupils.
• Pro tip : Repeat these steps at least 3–4 times to make sure that the measurement is correct.

Ask a friend

• Make your friend sit right in front of you in a crouching position.
• Look about 10–20 ft above your friend’s head. Do not look into his/her face.
• Keep your eyes as still as possible.
• Now, let your friend repeat the above mentioned steps for you and take the readings.