Adie's pupil is a condition characterized by an abnormally dilated pupil in one eye, which reacts poorly to light. This condition is often associated with damage to the autonomic nervous system, particularly affecting the parasympathetic nervous system. Individuals with Adie's pupil may experience blurred vision and difficulty focusing, especially in bright light. The affected pupil may also respond slowly to changes in light intensity, leading to a noticeable difference in size compared to the other pupil. This condition is usually benign and may not require treatment unless it causes significant visual disturbances.