Tricompartment model of the lacrimal pump mechanism.

BACKGROUND

The role of the lacrimal sac in the lacrimal pump mechanism is controversial.

METHODS

Movements of the lateral wall of the lacrimal sac with blinking were videotaped through an endoscope in eight patients after dacryocystorhinostomy. In addition, movements of an air bubble at the opening of the nasolacrimal duct with blinking were studied in three patients with an incompetent valve of Hasner.

RESULTS

The superior half of the lateral wall of the lacrimal sac moved laterally with lid closure and medially with lid opening. The inferior half of the lateral wall of the lacrimal sac moved medially with lid closure and laterally with lid opening. In patients with an incompetent valve of Hasner, the air bubble at the opening of the nasolacrimal duct bulged into the nose with lid closure and retracted into the nasolacrimal duct with lid opening.

CONCLUSIONS

A tricompartment model of the lacrimal pump is presented that incorporates these findings. With lid closure, the orbicularis muscle contracts, compressing the canaliculi and pulling the superior half of the lateral wall of the lacrimal sac laterally. This creates a lower pressure in the superior sac, allowing tears to be propelled from the canaliculi into the sac. At the same time, the inferior half of the lateral sac wall moves medially, creating a positive pressure in the inferior sac and nasolacrimal duct, thus forcing tears down the duct into the nose. With lid opening, the orbicularis muscle relaxes, allowing the canaliculi to open and the superior half of the lateral sac wall to move medially. The resulting negative intracanalicular pressure allows tears to flow from the lacrimal lake into the canaliculi, and the higher pressure in the superior sac closes the valve of Rosenmueller and forces tears from the superior to inferior sac and proximal nasolacrimal duct. At the same time, the inferior half of the lateral sac wall moves laterally, resulting in a negative pressure in the inferior sac and nasolacrimal duct.