Objective To evaluate lacrimal sac (LS) pump failure in patients with lower motor neuron facial nerve palsy (FNP) using ultrasound biomicroscopy (UBM).

Methods This was a prospective observational case series. Patients with unilateral lower motor neuron FNP of different aetiologies, age groups and gender were enrolled in this study. Anatomical patency was confirmed through irrigation of the lacrimal drainage system. The degree of lagophthalmos and House–Brackmann grade (HBG) were evaluated, and the dye disappearance test performed. UBM evaluation of the LS during opening and closure of the eyelids was performed for both sides; the control side and the side with assumed lacrimal pump failure (attributed to FNP). Any changes in the orbicularis oculi muscle and fluid turbulence within the sac were reported.

Results A total of 17 patients with unilateral lower motor neuron FNP were evaluated. The average age (±SD) was 33.2±20.1 years. UBM evaluation of control side LS showed obvious fluid turbulence of different patterns within the sac during opening and closure of the eyelids. Fluid turbulence was absent in the LS with HBG V and VI FNP and reduced in the LS with HBG III and IV FNP.

Conclusions UBM can be used as a safe, non-invasive and office-based tool to evaluate the LS pump.