Anisocoria

Image of eye with anisocoria
  • Difference in pupil diameters as viewed in dim illumination
  • May be physiologic (normal variant) if diameter difference is 1mm or less and both pupils react briskly and equally to light
  • Pathologic causes are eye inflammation (anterior uveitis) or trauma (including eye surgery), medication instilled in eye, damage to ciliary ganglion or ciliary nerves ("tonic pupil"), third nerve palsy, Horner syndrome
  • Call it pathologic if anisocoria greater than 1mm in dim illumination, one pupil constricts poorly to light, or pupil shape irregular
  • If you find ptosis on side of smaller pupil, consider Horner syndrome
  • If you find ptosis, diplopia, or abnormal eye movements or alignment, consider third nerve palsy
  • Irregular pupil shape suggests anterior uveitis, tonic pupil, and eye trauma (including intraocular surgery)
  • Remember that anisocoria can be caused by instilled anticholinergic or sympathomimetic eye drops, or accidental contamination from plants or medicated skin patches and aerosols
  • If pupil constricts very slowly to light and dilates very slowly when light is withdraw, consider tonic pupil caused by damage to ciliary ganglion or nerves in orbital disorders (including surgery)
  • Nothing—you should be able to tell if two pupils are different in size
  • Challenge is to decide whether anisocoria is pathologic
  • Measure amount of anisocoria in dim illumination; more than 1.5mm usually pathologic, especially if pupil constricts poorly to light
  • Refer to ophthalmologist if findings suggest pathologic anisocoria
  • Refer urgently if you suspect third nerve palsy (could be caused by intracranial aneurysm) or Horner syndrome (could be caused by arterial dissection or tumor)
  • Measure amount of anisocoria in dim illumination; more than 1.5mm usually pathologic, especially if pupil constricts poorly to light
  • Refer to ophthalmologist if findings suggest pathologic anisocoria
  • Refer urgently if you suspect third nerve palsy (could be caused by intracranial aneurysm) or Horner syndrome (could be caused by arterial dissection or tumor)