Topazolin (tetrahydrozoline) is a vasoconstrictor used in topical pharmaceutical formulations, primarily for ophthalmic and nasal applications. In eye drops, it reduces redness by constricting blood vessels in the conjunctiva, providing temporary relief from irritation caused by dust, smoke, or eye strain. In nasal sprays and decongestants, it shrinks swollen mucous membranes to alleviate congestion, sinus pressure, and allergy symptoms by improving airflow. It is available over-the-counter and offers localized effects with minimal systemic absorption when used as directed. Prolonged use should be avoided to prevent rebound congestion or redness.