diagnosis
Last reviewed 01/2018
The level of a complete lesion in Horner's syndrome can be identified by the use of pharmacological agents:
- 4% cocaine eyedrops fail to dilate the pupil in Horner's syndrome:
- cocaine inhibits the reuptake of noradrenaline, if there is no noradrenaline then cocaine is inactive
- hydroxyamphetamine will not dilate a Horner's pupil if the lesion is post-ganglionic
- weak adrenaline dilates a Horner's pupil when the lesion is post-ganglionic
In summary:
- a normal pupil is dilated by cocaine and hydroxyamphetamine
- when the lesion is pre-ganglionic only hydroxyamphetamine causes dilatation
- when the lesion is post-ganglionic only adrenaline causes dilatation