Last revised by Derek Smith on 11 Oct 2021

Anisocoria is present when an individual's pupils differ in size. If a person's pupils are symmetric there is said to be isocoria.


The prevalence of transient physiological anisocoria of >0.4 mm is found in up to 20% population. However persistent anisocoria seems to be rarer, in the same study it was only found in 3% subjects 1



Most cases are benign, the two diagnoses of concern are third nerve palsy and Horner syndrome, each of which has multiple causes (see individual articles).

  • third nerve palsy
  • Horner syndrome
  • medication: mydriatics (dilating agents) are more commonly the cause than miotics (constricting agents) 3
    • mydriatics
      • vasoconstrictors, hyoscine, glycopyrrolate antiperspirant, Jimson weed, angel's trumpet, blue nightshade
    • miotics
      • opiates, clonidine, organophosphates, pilocarpine, prostaglandins
  • physiological
  • local pathology of the iris (rare) e.g. trauma

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