Unilateral non-reactive mydriasis

Specialty: Ophthalmology.

• unilateral dilated and fixed pupil
• reactive pupillary asymmetry

Why it occurs

• Acute compressive palsy of the third cranial nerve (extrinsic compression due to aneurysm of the posterior communicating artery)
• Uncal brain herniation secondary to ipsilateral intracranial edema or expansile mass (Hutchinson's sign)
• Direct blunt or penetrating ocular trauma that causes physical rupture of the pupillary sphincter of the iris (traumatic mydriasis)
• Accidental or intentional exposure to substances with an atropinic effect (mydriatic ophthalmic eye drops, transdermal scopolamine patches, eye contact after touching plants rich in belladonna alkaloids)
• Unresolved acute angle-closure glaucoma (causing ischemia and irreversible paralysis of the iris sphincter)

Initial workup

Urgent neurological examination of ocular motility and pupillary reflexes (direct and indirect or consensual reflex); Ophthalmological examination in a slit lamp looking for visible tears or breaks in the margin of the iris sphincter; Urgent brain CT angiography or emergency brain MRI to immediately rule out a vascular aneurysm or expansile intracranial mass; Immediate measurement of intraocular pressure.

Standard management

• There are no pharmacological treatments indicated directly on the eyeball to constrict a pupil that presents neurological or severe ischemic paralysis. Management is etiological and neurological resuscitation. Mannitol 20% (intravenous infusion of 1.5 to 2 g/kg to be administered over 30 minutes if intracranial hypertension associated with uncal herniation is confirmed in the hospital emergency department).