A 26-year-old woman has unequal pupils with the right pupil being larger. What best describes this pupillary abnormality?

The correct answer is Adie's tonic pupil, which is characterized by a unilateral dilated pupil that reacts poorly to light but has a better response to accommodation. In this scenario, the right pupil being larger suggests a potential disruption in the autonomic nervous system. Adie's tonic pupil typically occurs due to damage to the parasympathetic fibers that control the sphincter muscle of the iris, leading to a dilated pupil that may appear slower to react.

This abnormality is often associated with other features, such as light-near dissociation, where the pupil constricts more when focusing on a near object than in response to bright light. It’s important to distinguish this from other conditions such as an afferent pupillary defect, which would manifest differently, and a third cranial nerve palsy, which might present with additional symptoms like ocular motor deficits or ptosis.

The Argyll Robertson pupil is typically associated with neurosyphilis and is characterized by pupils that constrict poorly to light but maintain a more normal response to accommodation, which does not correlate with the specific findings of a larger pupil in this case. Thus, Adie’s tonic pupil is the most appropriate description for the abnormality presented in this scenario.