Anisocoria is a disparity of pupil size. To determine the abnormal pupil, compare pupil sizes in light and dark. It is accentuated in the paretic muscle. If the iris sphincter (or its innervation) is involved, the anisocoria will be increased in bright light. If the iris dilator muscle (or its innervation) is affected, it will be more pronounced in darkness. Up to 20% of normal individuals have physiologic anisocoria of 1 to 2 mm.
Other causes of anisocoria with an abnormally large pupil include mydriatic drops, contamination from a scopolamine patch, an Adie pupil, and ocular trauma with iris sphincter damage. A dilated pupil due to anticholinergic agents (eg, atropine) does not react to light, although a dilated pupil due to sympathomimetics still has some response.
An abnormally small pupil may be secondary to Horner syndrome, chronic Adie pupil (8 weeks or more after the event), iritis, and eye drops (pilocarpine). Miosis secondary to pupillary sphincter muscle spasm may be transiently observed after ocular trauma, followed by mydriasis.
Management and Disposition
Evaluation is dependent on clinical presentation. A patient with the acute onset of 3rd-nerve palsy with associated headache or trauma should be evaluated as a neurosurgical emergency.
Pilocarpine may be helpful to differentiate the etiology of pupil dilation. With low concentrations (0.125%), an Adie pupil will constrict more than the unaffected eye secondary to denervation supersensitivity. With higher concentrations (1%), a pupil that fails to constrict is most likely secondary to topical anticholinergic mydriatics (scopolamine, atropine, or cyclopentolate). Unlike the mydriasis seen with intracranial pathology, pharmacologic mydriasis is not associated with pain, ptosis, or diplopia. Other pathology within the iris sphincter muscle that prevents constriction to 1% pilocarpine includes iris muscle trauma and synechiae.
A patient with a dilated pupil, ptosis, and abnormal extraocular movements should be evaluated emergently for an aneurysm or expanding supratentorial mass with tentorial herniation.
With physiologic anisocoria, the pupil size disparity is the same in light and dark, and there are no other ocular findings.
A driver’s license or ID badge may be helpful to document a preexisting anisocoria.
Some brands of eye makeup contain belladonna alkaloids, which can cause mydriasis.
An Adie pupil initially is dilated but may become miotic over time. It is a benign condition that affects young adults, affects women more often than men, and is associated with decreased reflexes.
Posttraumatic Anisocoria. Marked chronic anisocoria secondary to prior trauma as a child. (Photo contributor: R. Jason Thurman, MD.)