What effect does Phenylephrine have on conjunctival blood vessels?

Phenylephrine is a sympathomimetic agent that primarily acts as an alpha-1 adrenergic agonist. When applied to the conjunctiva, phenylephrine causes vasoconstriction of the conjunctival blood vessels. This vasoconstriction leads to a blanching effect, where the blood vessels become less perfused and appear paler or less vascular.

The mechanism involves the stimulation of alpha-1 receptors on smooth muscle cells lining the blood vessels. As these muscles contract, the diameter of the blood vessels decreases, reducing blood flow to the area. This is useful in various ophthalmic applications, such as reducing redness in the eyes.

In this context, the choice that describes the action of phenylephrine correctly emphasizes its ability to blanch conjunctival blood vessels by inducing vasoconstriction. This is why the selected answer accurately represents the pharmacological effect of phenylephrine on conjunctival blood vessels.