A pupil that does not react to stimuli.
A fixed pupil, referring to the circular opening in the center of the iris, is an abnormal condition where it does not respond to light or adjust during the process of focusing on objects (accommodation). This condition could indicate various eye disorders like acute glaucoma and uveitis, or in rare cases, a brain tumor affecting brainstem structures responsible for eye reflexes. If both pupils are fixed and dilated, it can be a sign of brain death.