When the dark circle in the center of your eye is larger than normal Dilated pupils (mydriasis) can happen for many reasons, such as a normal response to light, medication or drug use, eye exams ...

is a condition in which the pupil in one of your eyes spontaneously dilates. It can stay dilated for just a few minutes or can go for days before returning to its normal size, Mackay says.

Unequal pupils (anisocoria) may be a sign of a medical issue. Certain medications placed in the eyes can cause the pupils to ...