Why do most topical ophthalmic medications require several applications per day?

Topical ophthalmic medications require several applications per day primarily because the eye secretes tears. The tears serve multiple important functions, including lubrication and protection of the eye, but they also help to wash away foreign substances and medications. When a medication is applied topically, it can get diluted or washed away by the natural tear film and the blink reflex, which can significantly reduce its therapeutic effect.

As a result, frequent reapplication is often necessary to maintain effective drug concentrations within the ocular tissues, ensuring that the intended therapeutic action can take place. This is particularly crucial for treatments aimed at conditions like glaucoma, infections, or dry eyes, where sustained drug levels are needed to achieve desired outcomes.