Glossary · Eye area
Interpupillary distance
Interpupillary distance is the distance between the centres of the two pupils. It sets the middle of the facial fifths, and it is fixed by the skull, so it is structural. A phone lens close to the face distorts apparent eye spacing, so BecomeTen reports spacing as a band relative to eye width, not a number. Glasses fitting uses it.
Also called: IPD, eye spacing, pupillary distance, PD
What is interpupillary distance?
Look straight ahead and measure from the centre of one pupil to the centre of the other. That is the interpupillary distance, IPD, or in an optician's notes simply PD. It is decided by how far apart the orbits sit in the skull, and it stops changing when facial growth finishes. Forums use it to sort faces into close-set, average and wide-set eyes. BecomeTen rates eye spacing as one eye-area trait and reports it as a band.
How does IPD fit the facial fifths?
The facial fifths divide the face horizontally into five equal widths, each notionally one eye wide. The middle fifth is the gap between the eyes, the two beside it are the eyes, and the outer two run to the edge of the face. Interpupillary distance fixes the width of the central three fifths together. Pupils far apart relative to eye width make a wide middle fifth and the eyes read wide-set; close together, they read close-set. That is why BecomeTen reports spacing as a ratio band against eye width rather than a distance: the ratio is what the eye judges, and it survives changes of scale.
What a photo can and cannot show
A photo can show spacing relative to eye width, and it can show it wrongly. A phone lens a hand's width from the face is a wide-angle lens used close, and perspective enlarges whatever is nearest: the nose and the centre of the face grow, the sides fall away, and the ratio of eye spacing to face width shifts. Turn the head a little and the far eye shrinks. There is also nothing of known size in a selfie to scale against, so no app can honestly output the distance itself. BecomeTen reports a band with a capture grade, as its methodology requires. The fix is cheap: camera at eye level, an arm's length away, head square to the lens. See photo quality, light, angle and lens.
Is interpupillary distance workable or structural?
Structural, without exception. The orbits are bone and their spacing is set. BecomeTen tags eye spacing structural, the plan never promises to change it and the potential image is forbidden from redrawing it. The eye area's workable ceiling comes from the tissue around the eyes: brows, under-eye condition, skin and sleep.
What actually changes how eye spacing reads?
- Brows. Brow heads close to the bridge of the nose pull the eyes together visually; tidying the inner ends opens the middle fifth.
- Hair parting and volume. Volume at the sides widens the outer fifths, so the eyes read closer together. A centre parting makes spacing read as it is.
- Glasses. A frame's bridge width and lens position reframe the middle fifth. Lenses centred over the pupils read neutral; frames too wide for the face make the eyes look close-set.
- Lens distance. The single largest distortion in most selfies. Arm's length or further, every time.
One photo. Then stop guessing.
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Why do opticians measure IPD?
For a neutral, practical reason: the optical centre of each spectacle lens should sit in front of the pupil, or the lens introduces prismatic error and eye strain. An optician measures it with a ruler or a pupillometer against the real face, and the number goes on the prescription. It is a genuine measurement because the scale is known. That is exactly what a photo lacks, which is why the optician's number and a rating band should not be compared.
Questions
Can I use my optician's interpupillary distance to check my facial fifths?
Only half of it. The optician's number is a real distance, but the fifths are a ratio of spacing to eye width and face width, and you would need those measured the same way on the real face. A photo will not give them. BecomeTen skips the distance and reports the ratio band directly.
Does a wide interpupillary distance lower a BecomeTen score?
Not by itself. Spacing is one eye-area trait, tagged structural, and the model reads it as a band relative to eye width. Faces in the outer bands are not penalised for being there; the 2011 review finds averageness rated well, and the wide and close bands simply sit further from that middle. Skin, sleep and brows move the eye area more.
Why does my interpupillary distance look narrower in selfies?
Because a phone close to the face is a wide-angle lens, and perspective enlarges the centre of the face relative to the sides. The nose grows, the face narrows, and the ratio the eye judges shifts. Hold the camera at arm's length or further, at eye level, and the spacing band settles across scans.