The correlation of phenylephrine 1% with hydroxyamphetamine 1% in Horner's syndrome

Pharmacological testing in Horner's syndrome involves the use of cocaine to confirm the diagnosis and hydroxyamphetamine to localise the lesion to the post-ganglionic (third order) or non-postganglionic neuron. However, hydroxyamphetamine bromide 1% (Paredrine) is not always readily available to the ophthalmologist. An alternative drug for localising the site of the lesion is phenylephrine 1% which can easily be prepared by dilution of stronger concentrations (2.5% or 10%) and which is almost universally available in most ophthalmologists' offices. Because of the principle of denervation supersensitivity, a Horner's syndrome produced by a lesion interrupting the postganglionic fibres should dilate the pupil when phenylephrine 1% is placed in the conjunctival sac. The pupil of a patient with central (first order) Horner's syndrome should not dilate, while a pre-ganglionic (second order) pupil may dilate minimally ¹ ; a normal pupil may, at best, dilate minimally. The purpose of this study was to compare the pupillary response of patients with Horner's syndrome to phenylephrine 1% and hydroxyamphetamine 1%.

Fourteen consecutive patients with Horner's syndrome were prospectively tested with cocaine 10%, hydroxyamphetamine 1%, and phenylephrine 1% on separate days, at least 3 days apart. All pupils were measured in the same room lighting with a standard ruler 1 hour after instillation of two drops. Phenylephrine 1% was prepared on each examination day by diluting phenylephrine 10% hydrochloride (0.1 ml) with 0.9 ml of preservative free natural tear drops. The clinician interpreting each pharmacological test was masked to the results of the other pharmacological tests and the cause of Horner's syndrome.

Nine of the...