Interpupillary-to-face width ratio

Eyes can stay the same distance apart and look closer together inside broader cheeks. More width lies beyond the eye region, making it appear concentrated towards the centre. Inside a narrower face, the same pupil span occupies more of the available width.

Pupil spacing also differs from the gap between the inner eye corners. Long openings can place the pupils far apart even when the inner gap is modest. Short eyes around a large gap can look separated locally while still occupying a small share of a broad face.

A high ratio can reflect a wide inner gap that moves the eyes apart. If eye width stays similar, the empty space around the bridge becomes a larger part of the eye region. Long eyes can also increase pupil span, but more of that span is then occupied by the openings themselves.

Narrow cheeks raise the ratio around either arrangement. If eye width relative to the face is high too, the eyes may simply occupy a large share of a narrow outline. The inner gap helps show whether their prominence comes mainly from size or separation.

A low result can likewise reflect close pupils or broad cheeks. An ordinary eye arrangement inside a broad face looks different from a small, closely grouped pair inside a narrower one. Compare the openings with each other before attributing the result entirely to spacing.

The mouth provides a second horizontal span below the eyes. Widely spaced pupils can make an unchanged mouth look narrow beneath them. If the mouth is broad too, the central features may retain similar widths relative to each other while occupying more of the face.

Pupil spacing also contributes to midface ratio, where it is compared with eye-to-upper-lip height. Widening the pupils raises both ratios without shortening the face. The centre becomes wider in proportion, even though the nose and mouth remain at the same vertical positions.

A low pupil-to-face ratio alongside low relative eye width describes an eye region occupying little of the facial span. The inner gap then determines whether that region looks closely grouped or contains small eyes separated by appreciable space.

Pallett, Link and Lee altered eye and mouth placement within female faces and found preferred horizontal spacing near 46% of facial width. The eyes themselves could remain unchanged while their arrangement affected ratings.

Their facial-width measurement ran between the inner ear edges, whereas this ratio uses the cheekbones. The percentages therefore describe different spans. The 45–50% reference here places the pupils around half of cheekbone width, but the study does not directly validate those limits.

Eye-region dimensions and cheekbone width develop at different rates. If facial breadth grows faster than pupil spacing, the ratio falls even though the pupils may become farther apart. This can make the adult eye region look less prominent within the face than it did earlier.

Sforza's eye-region research and Fang's review of population variation describe differences in the component dimensions across samples. A typical value depends on those samples and their measurement methods. For comparisons within one person, direct gaze is important because looking to the side shifts the pupils inside otherwise unchanged openings.