anisocoria

A condition where someone’s pupils are not the same size. It can be caused by abnormal brain activities (often severe difference in size), a reaction to eye injury or a harmless sign of an unsymmetrical body (which is often more common than a symmetrical body. Anisocoria due to this cause is often only a small difference that can go unnoticed.)

If you have a big and easily noticable difference in your two pupils and do not remember having an eye injury, make sure to visit a doctor or other professional.