Current pharmacologic testing for Horner syndrome.

First described in 1727, Horner syndrome occurs from injury to one of the three neurons in the oculosympathetic pathway. Its presence can be confirmed with pharmacologic testing, traditionally including cocaine testing with hydroxyamphetamine localization. More recently, apraclonidine testing has become a viable alternative in some practices. Concern has been raised regarding the possibility of false-negative results with apraclonidine testing as well as the safety of its use in young children.