Tachyphylaxis With Sustained Apraclonidine Use in the Treatment of Ptosis Associated With Horner Syndrome

Apraclonidine is an adrenergic agonist with stronger affinity for α2 receptors than α1 receptors. Following sympathetic denervation in Horner syndrome, α receptors are upregulated, and therefore apraclonidine causes both mydriasis, via the effect of α1 stimulation of the dilator pupillae, and lid elevation, via the effect of α2 stimulation on Müller's muscle. In addition to being helpful in confirming Horner syndrome, apraclonidine can be used as a therapeutic agent for ptosis