The nasolacrimal sac is a small structure located in the inner corner of the eye. It is part of the nasolacrimal system, which is responsible for draining tears from the eye into the nasal cavity. When you blink, tears are produced by the lacrimal glands and flow across the surface of the eye, eventually entering the nasolacrimal sac through tiny openings called puncta. This sac connects to the nasolacrimal duct, which leads to the nasal cavity. If the nasolacrimal system is blocked or not functioning properly, it can lead to excessive tearing or infections. Conditions affecting the nasolacrimal sac may require medical evaluation or treatment.