An Adult With Unilateral Mydriasis

Karima S. Khimani; Rod Foroozan, MD


October 04, 2017

Case Diagnosis

Isolated anisocoria in the absence of ocular misalignment and ptosis raises suspicion for a tonic pupil. This diagnosis is further confirmed by the absence of other neurologic or systemic findings and a normal CT and MRI of the brain.

Argyll Robertson pupil is a feature of tertiary syphilis and can occasionally be clinically distinguished from a tonic pupil.[1] Argyll Robertson pupils are usually bilateral and miotic. They react with the near response but are fixed to stimulation with light. In contrast, the tonic pupil is usually unilateral and mydriatic. It has a delayed response to light and near, with tonicity to a near target. An Argyll Robertson pupil can be confirmed with serologic testing for syphilis.[1] This patient had no signs of syphilis and presented with a unilateral mydriatic pupil. Because of the overlapping clinical findings of a tonic pupil and Argyll Robertson pupil, serologic testing for syphilis is typically suggested if a tonic pupil is noted bilaterally.

Miller Fisher syndrome (MFS) is characterized by a triad of ophthalmoplegia, ataxia, and areflexia.[2] The diagnosis can be further supported by elevated levels of the anti-GQ1b antibody. Although most patients initially present with diplopia, pupillary involvement can occur in 50% of patients. Treatment with intravenous immunoglobulin can accelerate the recovery in some patients.[2] This patient had a unilateral tonic pupil, but he did not have areflexia and ataxia, which are diagnostic features of MFS.

A Hutchinson pupil occurs from compression of the third cranial nerve due to a mass lesion typically from trauma, tumor, or aneurysm. Mechanical pressure on the nerve can cause isolated mydriasis due to the superficial location of the parasympathetic nerve fibers on the oculomotor nerve. Patients usually present with ophthalmoplegia in addition to a dilated pupil, and they may have elevated intracranial pressure.[3] If a Hutchinson pupil is suspected, brain imaging is typically necessary to assess for an intracranial mass, hemorrhage, or aneurysm, as well as an orbital tumor or fracture. This patient had no history of trauma, his extraocular movements were normal, and there was no ptosis. CT and MRI of the brain showed no abnormalities that would suggest the presence of an intracranial mass effect.

Clinical Course

Six months after initial presentation, the anisocoria remained unchanged. However, he noted a decrease in the size of his right pupil on some days. He denied diplopia or ptosis. The patient continued having blurred vision with reading. His uncorrected near vision was J1 bilaterally.

The diagnosis of a tonic pupil was made, and the patient was instructed to follow up in 1 year or as needed.


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