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Matthew J. Thurtell

, and Robert L. Tomsak

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date: 17 January 2021

A difference in the size of the pupils (anisocoria) is a frequent finding on physical examination. While often a cause for alarm, it is not uncommonly physiologic. In this chapter, we begin by reviewing the innervation of the iris sphincter and dilator muscles. We next introduce clinical strategies that can help to determine the etiology of anisocoria. We describe the components of the pupil examination, which includes an evaluation of pupil size in bright light compared to darkness, as well as evaluation of the pupil shape, response to light, and response to near. We include an algorithm that summarizes the clinical approach to anisocoria. Lastly, we review the clinical features of physiologic anisocoria, which occurs in up to 20% of the normal population and does not require further diagnostic testing.

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