Anisocoria

Unequal pupil size. Physiological (simple) anisocoria is present in about 20 percent of the population, up to 1 mm, remains the same in light and dark and shows normal reactions.

• Pathological anisocoria is a sign of disorders of the sympathetic or parasympathetic pathway, iris disease or pharmacological effect.
• Causes: Horner syndrome (small pupil abnormal), third nerve palsy, Adie tonic pupil, pharmacological mydriasis (atropine, scopolamine patches, ipratropium nebuliser, plant exposure to Datura and belladonna), pharmacological miosis (pilocarpine, opioids), iris sphincter tear after trauma, iritis with synechiae, acute angle closure, post-surgical iris damage, uncal herniation.

• Anisocoria greater in the dark: the smaller pupil is the abnormal one (sympathetic deficit: Horner syndrome, with dilation lag) or physiological.
• Anisocoria greater in bright light: the larger pupil is the abnormal one (parasympathetic deficit: third nerve palsy, tonic pupil, pharmacological, sphincter damage).
• Third nerve palsy: ptosis, ophthalmoplegia, fixed dilated pupil.
• Adie: segmental palsy with vermiform movements and light near dissociation.
• Pharmacological: very large pupil (8 to 9 mm), no reaction, no ptosis or motility problem, no response to 1 percent pilocarpine.
• Traumatic: irregular pupil, sphincter tears, iridodialysis, hyphema.
• Acute angle closure: mid-dilated oval pupil, red painful eye, raised pressure.
• Emergency features: coma with a unilateral fixed dilated pupil indicates uncal herniation; neck pain with a small pupil indicates carotid dissection.

• Measure pupil diameter in bright and dim light with a pupil gauge; check the swinging flashlight test for relative afferent pupillary defect; examine the near response.
• Slit lamp for sphincter atrophy, tears, synechiae, transillumination defects and anterior chamber activity.
• Check lid position, ocular motility, corneal sensation and sweating.
• Pharmacological tests:
  • 1 percent pilocarpine: no constriction in a pharmacologically dilated pupil; constriction in a tonic or third nerve pupil.
  • 0.1 percent (dilute) pilocarpine: constriction indicates denervation supersensitivity (Adie, some third nerve palsies).
  • Apraclonidine 0.5 percent: dilation of the small pupil confirms Horner syndrome; cocaine 4 or 10 percent can substitute.
• Imaging: urgent CT angiography or MR angiography for a painful or pupil involving third nerve palsy; angiography of the neck for painful Horner; MRI orbits and brain for other neurological signs.

• Physiological anisocoria needs no treatment.
• Treat the cause: aneurysm repair, carotid dissection antithrombotic therapy, relief of raised intracranial pressure (head elevation 30 degrees, mannitol 0.25 to 1 g/kg IV, hypertonic saline, neurosurgical decompression) for herniation.
• Acute angle closure: acetazolamide 500 mg IV or orally, topical timolol 0.5 percent, pilocarpine 2 percent after pressure begins to fall, apraclonidine 1 percent, followed by laser peripheral iridotomy.
• Pharmacological mydriasis: remove the agent; pupil recovers over days (atropine up to 2 weeks).
• Traumatic sphincter damage: manage hyphema or iritis with topical prednisolone acetate 1 percent four times daily and cycloplegia (cyclopentolate 1 percent twice daily); iris repair or cosmetic contact lenses when symptomatic.
• Glare and photophobia in large pupils: tinted lenses, pilocarpine 0.0625 to 0.125 percent; iris print contact lenses or pupilloplasty when severe.