Why is pupil diameter taken into account?

Average pupil size changes significantly over the course of a person’s life. With increasing age, the pupil also loses some of its ability to dilate widely. Observations show a 50% change in maximum pupil dilation, from almost 8.0 mm to around 4.0 mm. However, considerable variability can also be observed within the same age group, including in people with presbyopia.

For subjective perception when looking through a specific area of a spectacle lens, the effect across the entire pupil ray bundle must be considered. Since area increases with the square of the radius, even small differences can have a noticeable impact on vision. In progressive lenses, taking the actually measured individual average pupil size throughout the day into account can support optimisation of the vision zones and further improve visual quality.