Pupillary Reflex; Roadside to Resus

Pupillary assessment provides critical diagnostic and prognostic data for patients with neurological impairment, yet its value depends on understanding the underlying anatomy and clinical context. The sympathetic dilation pathway follows a long route through the spinal cord, while the parasympathetic constriction pathway remains within the cranium. This distinction helps differentiate between benign physiological anisocoria and life-threatening conditions like intracranial mass effect or third nerve palsy. In cases of traumatic brain injury, serial documentation of pupil size and reactivity is essential to detect neurological deterioration, as these signs often precede clinical decline. While fixed, dilated pupils during cardiac arrest reflect brainstem hypoperfusion rather than a definitive outcome, they serve as a specific prognostic indicator 72 hours post-resuscitation. Accurate interpretation requires integrating these findings with the patient's full clinical picture, including potential drug exposures and ocular history, to avoid misdiagnosis.