What does a "fixed and dilated" pupil indicate?

A "fixed and dilated" pupil is a significant clinical sign that indicates potential brain injury or a severe neurological issue. This condition occurs when the pupil does not respond to changes in light, remaining wide and unchanging, which can suggest a disruption in the neural pathways that control pupil size. This can be indicative of increased intracranial pressure, direct brain injury, or even brain death.

In contrast, normal neurological function is characterized by pupils that react appropriately to light, constricting in bright light or dilating in dim lighting. A reaction to light involves the pupils changing size in response to illumination, clearly showing they are functioning normally. An allergic reaction typically does not cause fixed and dilated pupils but may cause other symptoms such as swelling or redness in the eyes. Thus, when assessing a patient with fixed and dilated pupils, the focus should be on potential neurological compromise, making it critical to seek further evaluation and management.