PD
PD (Pupillary Distance) is the distance between your pupils, measured in millimeters. Your pupils are the dark centers of your eyes that widen to let in light or narrow to focus on close objects.
Average PD ranges
- Most adults have a single PD between 50 mm and 70 mm, with the average around 63 mm.
- PD stabilizes in the late teens and generally remains constant through adulthood.
- Men tend to have slightly wider PDs than women on average.
Types of PD
| Type | What It Measures | Example |
| Single PD (Binocular) | The total distance from the center of one pupil to the center of the other | 63 mm |
| Dual PD (Monocular) | Two numbers: the distance from the center of the nose bridge to the center of each pupil | 31/33 mm (right/left) |
PD Measurement Is Critical for Glasses
It ensures the optical center of your prescription lenses aligns precisely with your pupils. Misalignment introduces unwanted prismatic effects, which can compromise your vision in several key areas.
Comfort
When the optical center does not match someone’s pupil position, his brain has to work harder to fuse the images from both eyes. This extra effort can lead to noticeable daily discomfort.
- Eye strain and fatigue after short periods of reading or screen time.
- Tension headaches, particularly around the temples.
- Blurry or double vision (diplopia).
- A persistent “off” feeling or difficulty adapting to new glasses
Optical Physics
For example, a 1 mm decentration error on a +4.00 D lens induces approximately 0.4 prism diopters per eye. This means that the stronger your prescription, the more significant the visual disturbance from even a 0.5 mm PD error.
Conversely, for low prescriptions (e.g., ±1.00D), the same 1 mm error induces only about 0.1 Δ—which most wearers can tolerate comfortably.
