Medications, trauma, and medical conditions can lead to abnormally small pupils (miosis). In miosis, the pupil is smaller than it should be, even in darkened conditions when it would typically ...

Nocturnal animals tend to have proportionally bigger eyes than humans do. They also tend to have pupils that open more widely in low light. So, at the outset, nocturnal eyes gather more light than ...

The peripheral drift illusion causes us to perceive motion in a still image. A new study shows that the mechanism of this illusion relies on changes in pupil size.

Fish like roach that migrate between lakes and streams have larger eyes with bigger pupils, improving vision in low light.