Perioperative unilateral mydriasis is a disturbing finding, which is suggestive of acute intracranial pathology during general anesthesia. In addition, the assessment of an abnormal neurological injury is limited during general anesthesia, with anisocoria requiring special consideration. The case of a 27 year old healthy male patient, with ipsilateral mydriasis found near the end of surgery of open reduction for left blow out fracture, was experienced. The patient's pupils were bilaterally equal four hours after uneventfully surgery. The possible causes of unilateral mydriasis include the effects of anesthetic agents, stellate ganglion block, impaired venous return from head and neck, an acute intracranial mass lesion or hemorrhagic event, direct eye trauma, pre-existing medical or surgical conditions (Adie's tonic pupil, artificial eye etc.) and inadvertent direct deposition of α-adrenergic or anticholinergic agents in the eye. The understanding and diagnosis of unusual mydriasis during general anesthesia requires knowledge of the autonomic nerve pathways and pharmacology of the eye. In this case, the myadriasis of the left eye was considered to have resulted from the absorption of 1:100.000 topical epinephrine infiltrated into the lower eyelid via episcleral vessels.