Anisocoria in Focus: A Case of Patient Distress When the Mirror Signals Trouble.

Anisocoria, characterized by unequal pupil diameters typically ranging from 0.3 mm to over 2.0 mm, represents a clinically significant finding that requires thorough evaluation in the emergency department. This asymmetry may indicate dysfunction of the cranial nerves or iris musculature, thereby providing valuable insight into the integrity of the autonomic nervous system. Although anisocoria may be physiologic or benign, it can also serve as a warning sign of severe neurologic or ophthalmologic pathology, including intracranial hemorrhage, oculomotor nerve palsy, or Horner syndrome. In the absence of overt trauma, the diagnostic process may be complicated by a lack of clear clinical indicators, potentially delaying appropriate intervention. Timely recognition and accurate differentiation between benign and pathologic causes are critical, given the association of anisocoria with high-risk neurologic emergencies, pharmacologic influences, and considerable patient distress. This case report details the presentation of a previously healthy 40-year-old man who arrived at the emergency department with acute-onset anisocoria. It includes a comprehensive review of the underlying pathophysiology, clinical manifestations, diagnostic algorithms, and therapeutic considerations. Particular emphasis is placed on the role of a meticulous history and focused physical examination in guiding prompt and effective clinical decision making.