The narrowest part of the bony nasolacrimal canal: an anatomical study.

Purpose: To determine the narrowest diameter of the bony nasolacrimal canal.
Methods: Fifty-eight bony nasolacrimal canals from 29 Japanese cadavers (12 men and 17 women; average age at death, 83.4 years; range, 70-99 years) had been fixed in 10% buffered formalin before use. After exposing the medial (44 canals) or posterior half (14 canals) of the bony nasolacrimal canal, the part with the shortest anteroposterior or transverse diameter was determined on inspection. These positions from the canal entrance were measured, and the distance ratio, indicating where the shortest diameter was located in relation to the total length of the canal, was calculated.
Results: The shortest anteroposterior and transverse diameters were at the entrance to the canal in 32 of 44 canals (72.7%) and in 9 of 14 canals (64.3%), respectively. In the other canals, the shortest anteroposterior and transverse diameters were located at an average of 3.6 and 5.6 mm from the entrance, and the distance ratios were 29.0% and 46.7%, respectively. The mean shortest anteroposterior and transverse diameters were 5.6 and 5.6 mm, respectively.
Conclusions: The shortest anteroposterior and transverse diameters were at the entrance of the canal in most of the bony nasolacrimal canals. These results are comparable with the rate of obstruction at the canal entrance in primary acquired nasolacrimal duct obstruction.