How to Measure PD (Pupillary Distance) at Home

The PD (Pupillary Distance) is very important when ordering glasses, helping the lenses to be centered correctly over the pupils. If you know how, you can measure PD accurately at home. This article provides a detailed guide on how to quickly measure PD using just a PD ruler or a mobile app.

What is PD and Why is it Important?

• The eyes have to strain more to see through the incorrect part of the lens.
• It can cause eye strain, headaches after wearing for a period.
• Vision may appear distorted or blurry at the edges of the lenses.
• For progressive lenses, an incorrect PD will render the glasses nearly unusable.

There are two types of PD:

• Total PD (binocular PD): The total distance between the two pupils.
• Monocular PD: The distance from the bridge of the nose to each individual pupil (usually noted as 31/32mm).

Methods to Measure PD at Home

There are three common ways to measure PD at home:

Method 1: Using a Regular mm Ruler

This is the simplest method, requiring just a ruler with millimeter markings and a mirror.

• A ruler with mm markings (a clear plastic ruler is preferable)
• A large wall mirror
• A pen and paper for notes

Method 2: Asking Someone Else to Measure

The most accurate way to measure at home is to ask someone else for help. The person measuring should stand about 40cm away, hold the ruler, and read the measurement.

Method 3: Using a PD Measurement App on Your Phone

There are many mobile apps available that support PD measurement using the camera. Some popular apps include:

• EyeMeasure (iOS)
• GlassifyMe (Android/iOS)
• PD Meter (Android)

These apps use the front camera and facial recognition algorithms to measure PD. While convenient, their accuracy is often less than manual measurement by 1–2mm.

Detailed PD Measurement Guide (Using a Ruler)

Step 1: Preparation

Step 2: Measure the Right Eye First

• Close your right eye and open your left eye.
• Align the 0mm mark of the ruler with the center of your left pupil.
• Keep the ruler steady and do not move it.

Step 3: Measure the Left Eye

• Close your left eye and open your right eye.
• Look in the mirror and read the number on the ruler at the position of the center of your right pupil.
• That number is your total PD.

Step 4: Repeat 3 Times

Measuring Monocular PD

To measure monocular PD for each eye:

• Ask someone to stand opposite you.
• Place the ruler horizontally across the bridge of your nose.
• Read the distance from the center of the nose bridge to the center of each pupil.
• Monocular PD is usually noted as: Left PD 31mm / Right PD 32mm.

Important Notes When Measuring PD

Keep the Ruler Steady

Look Straight Ahead

Your eyes should look straight ahead, not to the side. When asking someone to measure, they should stand opposite you so you can look directly into their eyes.

Appropriate Measurement Distance

• Measure PD for distance glasses: Look at an object far away (or a mirror at a distance of 20-30cm).
• Measure PD for reading glasses: Look at an object about 30-40cm away. Near PD is usually 2-3mm smaller than distance PD.

When to Measure Again?

• PD in adults changes little over time.
• Children need to have their PD measured each time they change glasses as their faces are still developing.
• If you change frame styles (from large frames to small frames), it’s advisable to check PD again.

Reference PD Table by Age

Conclusion

Measuring PD at home is not difficult if you do it correctly. Use a mm ruler, measure at least 3 times, and take the average. If you are unsure about the results, visit an eyewear store to have it measured with specialized equipment.

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