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pupil (of the eye)
one's eyes
彼女の澄んだひとみに心を奪われた。
I was captivated by her clear eyes.
彼女の大きな眸が印象的だった。
Her large eyes were striking.
目のひとみは光の量によって大きさが変わる。
The pupil of the eye changes size depending on the amount of light.