Mydriatic agent phenylephrine

Phenylephrine is an effective mydriatic agent frequently used to facilitate examination of the retina. It is also a useful decongestant for minor allergic hyperemia and itching of the conjunctival membranes. Sympathomimetics administered as ophthalmic drops are also useful in localizing the lesion in Horner s syndrome. (See An Application of Basic Pharmacology to a Clinical Problem.)... 

Mydriatic agents containing tropicamide and phenylephrine hydrochloride (nurses)... 

Many of the adrenergic agents produce a transient, incomplete mydriasis when applied to the eye. Cycloplegia does not occur. Ephedrine sulfate in a 3% concentration has been used for this purpose. As has been indicated, the effect is most positive in Caucasians with light-colored irides. Ephedrine is not considered to be a good mydriatic, as it is none too reliable and its solutions are quite irritating to the cornea. Phenylephrine should probably be the adrenergic mydriatic of choice. 

Another study compared the mydriatic effect of 2.5% phenylephrine to 1% hydroxyamphetamine in a group of 28 young adult subjects without ocular disease. The two agents produced a nearly equal pupillary dilation (Figure 8-3). The maximum effect with both drugs occurred at approximately 45 minutes. 

Phenylephrine is a sympathomimetic aj adrenoceptor agonist capable of producing mydriasis in some species by iris dilator muscle contraction. In the horse, topical application of a 10% solution has been shown to have no effect on the pupil diameter in the normal eye. However, 10% phenylephrine in combination with topical atropine is reported to be useful in reversing pupillary spasm in some stubborn cases of anterior uveitis, although there is no pharmacological evidence to support any additive mydriatic effect when the two agents are used together. 

Given intravenously, phenylephrine is useful in the therapy of paroxysmal atrial tachycardia (PAT), or as a pressor agent in hypotensive states. Used topically, it reduces blood vessel diameter and thus is useful as a decongestant, hemostatic agent, or to reduce swelling of inflamed tissues, or as a mydriatic. It is also used systemically in the therapy of frequent urination. 

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