Cholinergic Supersensitivity of the Pupil: Has Testing for It Outlived Its Diagnostic Utility?

Supersensitivity is the behavior of an effector organ following denervation whereby it demonstrates enhanced function in response to a stimulus that was previously too weak to generate such a response. Demonstrating supersensitivity of the iris sphincter in response to a topically-applied dilute cholinergic agonist has become a standard diagnostic tool to confirm Adie's pupil. In fact, this procedure is now so firmly entrenched as an associated finding of Adie's pupil that many physicians are reluctant to diagnose this condition without pharmacologic confirmation, despite the presence of diagnostic pupillary signs (e.g., light-near dissociation and segmental palsies of the iris). But, the performance and interpretation of this test is filled with pitfalls that make it far less reliable than its inflated reputation would have you believe. What are the patient and test factors that influence the result? What defines an endpoint for a ""positive"" test? How sensitive is it? How specific is it? As you ill read in the discussion that follows, my bias is that testing for supersensitivity is an overrated procedure that rarely contributes to the diagnosis of Adie's pupil.