Additionally, which drug is also used to identify the nature of Horner's syndrome lesions?

In the context of diagnosing Horner's syndrome, hydroxyamphetamine is particularly valuable. This drug helps differentiate between pre- and post-ganglionic lesions affecting the sympathetic innervation to the eye. When hydroxyamphetamine is administered, it causes the release of norepinephrine from sympathetic nerve terminals.

If a pre-ganglionic lesion is present, there would be sufficient stores of norepinephrine, and the pupil will dilate in response to the drug. Conversely, if the lesion is post-ganglionic, there would be a lack of norepinephrine available, resulting in no response to hydroxyamphetamine, thus indicating the location of the sympathetic disruption.

Knowing this mechanism, it's easier to understand why hydroxyamphetamine is a preferred choice in this diagnostic process, as it offers a clear indication of the type of lesion involved in Horner's syndrome. Other drugs listed, while useful for different indications in ophthalmology, do not have the diagnostic utility for this specific purpose.