<p>Zinc ions, the active compound of zinc sulphate, have an astringent, i.e. tissue-sealing and slightly anti-septic effect. Naphazoline constricts the blood vessels and reduces the inflammation and swelling of the conjunctiva. This effect of naphazoline, a substance of the benzylimidazoline group, is due to direct binding to a-adrenergic receptor sites on unstriated muscle cells in the blood vessels.</p>