What does pupil dilation mean?

A normal human pupil is about 2.5 to 4.0 mm in diameter under diffuse natural light, and a dilated pupil is one that is greater than 5 mm in diameter. A dilated pupil can be a physiological response to weakening light and strong emotional changes (reflex to light), or it can be caused by eye disease or cranial disease and epilepsy.

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