Pharmacological tests for Horner’s Syndrome

1) COCAINE 4%

-Blocks re-uptake of norepinephrine at the pre-synaptic cleft allowing more norepinephrine to function in stimulation of the pupillary dilator muscle.
-The response of a normal pupil to cocaine 4% is dilation
-The response of a Horner syndrome pupil to cocaine is no or poor dilation because there is a shortage of norepinephrine in the synaptic cleft.
-Despite blockage of pre-synaptic norepinephrine reuptake by cocaine in a Horner syndrome eye, there is already limited norepinephrine in the
synaptic cleft to cause dilation.


2) APRACLONIDINE 1%

-Weak alpha2-agonist activity, with little effect on the normal pupil.
-Horner pupil will dilate much more than the normal pupil after instillation of apraclonidine as a result of the dominant alpha1 effect from adrenergic receptor super-sensitivity


3) HYDROXYAMPHETAMINE 1%

-Stimulates release of preformed noradrenaline
-Hydroxyamphetamine eye drops dilation of both pupils indicate a lesion of the 1st or 2nd order neuron
-If the smaller pupil fails to dilate, it indicates a lesion of the 3rd order or post-ganglionic neurone


4) PHENYLEPHRINE 1%

-Non selective alpha agonist
Phenylephrine 1% has no effect on a healthy pupil
-Phenylephrine 1% has no effect on a 1st and 2nd order Horner’s
-Dilation of pupil indicates a 3rd order Horner’s due to supersensitivity

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