It is a curious fact that air, except in minimal amounts, is not often found in the lacrimal sac, despite its anatomic connection with the nose. One of the earliest tests (1823) for patency of the lacrimal passages was to have the patient blow the nose and feel or hear the exit of air from the lacrimal puncta; this, however, does not hold in most persons. According to Duke-Elder,1 about 5% of persons can whistle through their eyes, as it were, when air is forcibly exhaled with the nose closed, and some can emit smoke in the same manner.
The nasolacrimal duct is an irregular passage lined with mucous membrane which has a variable number of folds, or valves, the function of which is uncertain. The fold at the lower orifice of the nasolacrimal duct, known as the valve of Hasner, is thought to be a barrier to the
LEVITT JM, KRAVITZ D. Lacrimal Air Anomalies. AMA Arch Ophthalmol. 1959;61(1):9-13. doi:10.1001/archopht.1959.00940090011002