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Emergency Medicine

Training Level

Resident PGY 3


Henry Ford Macomb


Anisocaria is a condition characterized by unequal pupil size. The potential causes of anisocaria range from benign to potentially life threatening processes. Therefore, determining the etiology is of great importance. Mydriasis, more specifically, is when anisocaria is caused by an abnormally dilated pupil. There are several well-known causes of this phenomenon, however the objective of this clinical case study is to present an unusual cause of mydriasis to help provide more insight into a potentially challenging diagnosis. A 14-year-old female presented to the ED with chief complaints of sore throat, fatigue, and a dilated left pupil. She reported headache at the time of symptom onset, however that resolved prior to presentation. She wears contact lenses, changing them daily, and denied any changes to her regimen or exposure to any chemicals. She denied any traumatic injury, visual changes, and only noticed that her pupils were different in size because somebody else informed her. On exam, patient’s pupils unequal, with left pupil approximately 4mm larger than right. Both pupils were round, and reactive to light. Fundus exam was normal. No other focal neurological deficits were noted. Other physical exam findings where positive for anterior cervical lymphadenopathy, and posterior oropharyngeal erythema. Testing in ED was significant for positive infectious mononucleosis antibody screen. Patient had no other findings concerning for malignant underlying process, so she was discharged home with symptomatic treatment of mono, instructions to remove contact lens, and to follow up ophthalmology. After discharge, patient was evaluated by ophthalmologist, and subsequently referred to neuro-ophthalmologist due to unexplained persistent mydriasis. Prior to neuro-ophthalmology evaluation, her symptoms resolved, 8 days after initial onset. After further workup by neuro-ophthalmologist, it was determined that her transient mydriasis was related to autonomic nervous system irritability secondary to regional inflammation from infectious mononucleosis pharyngitis. Anisocaria results from one pupil having either impaired constriction or dilation. The parasympathetic and sympathetic pathways mediate these processes. To determine which pathway is involved, examination in light/dark conditions, and evaluating pupillary response to light and near stimuli is used. In mydriasis, the anisocaria is greater in light conditions, signifying an abnormal ability to constrict, or in other words, an interruption in normal parasympathetic function. Common causes of mydriasis include trauma, oculomotor nerve palsy, tonic pupil (damaged to ciliary ganglion or short ciliary nerves), or pharmacologic causes with drugs such as atropine, phenylephrine, clonidine, apraclonidine, cyclopentolate, scopolamine patches, aerosolized ipratropium, and jimsonweed. Infection is not typically considered one of the common causes of this condition, but as seen in the case presented, do not forget to include it in your differential, as this knowledge may aid in early diagnosis and help to prevent unnecessary testing and further workup.

Presentation Date


Case Study: Infectious Mononucleosis, A Rare Cause of Transient Mydriasis