IPA: /ˌɪntəˈpjuːpɪˌlɛri/
KK: /ˌɪntərˈpjuːpɪˌlɛri/
Relating to the space or distance between the pupils of the eyes.
The interpupillary distance is important for fitting glasses properly.
Interpupillary → It is formed from "inter-" (meaning between) and "pupilla" (from Latin, meaning pupil of the eye). The word refers to the distance between the pupils of the eyes.
Think of the distance that is 'between' ('inter-') the 'pupils' ('pupilla') of the eyes to remember that interpupillary refers to that specific measurement.
No commonly confused words.