Question of the Week

You are the resident on call when a 72-year-old man presents with complaints of glare and a dilated left pupil. One week ago, he underwent uncomplicated cataract surgery on the same eye. Postoperative care included topical antibiotics and anti-inflammatory drops. On postoperative day 1, his left pupil was noted to be 7 mm compared to 3 mm on the right. He reports no pain, and there was no corneal edema or elevated intraocular pressure. Examination now reveals a round, fixed dilated pupil that fails to constrict to topical 2% pilocarpine. Weeks later, iris atrophy is noted.

What is the most likely diagnosis?

A. Horner syndrome
B. Urrets-Zavalia syndrome
C. Pharmacologic mydriasis
D. Intraoperative iris sphincter damage

Answer

Urrets-Zavalia syndrome is a rare complication of cataract or other anterior segment surgery. It is characterized by persistent, fixed mydriasis, resistance to pilocarpine, and eventual iris atrophy. The most likely underlying mechanism is iris ischemia, often associated with elevated intraocular pressure or trauma during surgery. Iris ischemia damages the sphincter muscles and prevents normal pupil constriction. Horner syndrome (A) is incorrect because Horner syndrome causes miosis (pupil constriction) on the affected side due to disruption of sympathetic innervation. This is the opposite of the presentation here, where mydriasis (pupil dilation) is observed. Pharmacologic mydriasis (C) is incorrect because pharmacologically dilated pupils (e.g., due to tropicamide or atropine) would resolve over time as the drug wears off. Additionally, these pupils would typically respond to pilocarpine because the iris sphincter remains functional, unlike in Urrets-Zavalia syndrome. Intraoperative iris sphincter damage (D): while trauma to the iris sphincter can cause a dilated pupil, it would typically result in an irregularly shaped pupil, not the round pupil observed here. Furthermore, intraoperative damage alone does not account for the iris atrophy seen weeks later.

Source:

11.Kawasaki AK. Diagnostic Approach to Pupillary Abnormalities. Continuum (Minneap Minn). 2014;20(4 Neuro-ophthalmology):1008-1022. doi:10.1212/01.CON.0000453306.42981.94