Circular opening in the centre of the eye is called pupil. It allows the light to pass through it. The pupil expands when there is little light and contracts when there is greater light. Unequal pupil size or anisocoria refers to an unequal pupil size. Anisocoria is a condition characterized by an unequal size of the pupils. This condition causes one of the dog's pupils to be smaller than the other.
The most noticeable symptom is when your dog has one pupil that is visibly smaller than the other.
