Background: Surgical importance of the nasolacrimal duct (NLD) for both otolaryngologists and ophthalmologists cannot be overemphasized. Injury to this structure can lead to iatrogenic epiphora, synechiae formation and need for secondary lacrimal diversion procedures. Materials and methods:The present study was conducted on 27 mid-sagittal sections of head and neck of formalin fixed adult cadavers. The inferior opening of the NLD was identified and exposed. The duct and the lacrimal sac were dissected. Pertinent distances of the inferior opening of the NLD from the easily identifiable surgical landmarks were recorded, so as to accurately locate the inferior opening of the duct using a digital vernier calliper (accuracy 0.02 mm, Mitutoya, Japan). Various dimensions and angulation of the duct and lacrimal sac were measured. Results:The average length of NLD was 11.42 ± 2.45 mm and it was making an angle of 20° with the vertical plane. The duct was narrowest in caliber in its upper 1/3rd in majority (82%) of the cases. The average diameter of the inferior opening of the NLD was 3.14 mm. In two cases (7.4%), the opening was only 1.8 mm wide. The mean distance of the inferior opening of the duct was 20.7 mm from the columella, 25.5 mm below the skull base and 16.5 mm above the hard palate. The average distance between the inferior opening of the NLD and anterior end of the inferior turbinate was 14.8 mm. The mean A-P diameter of superior opening of NLD was about 3 mm. The average length and width of nasolacrimal sac at its center was 6.95 and 3.24 mm respectively. Conclusion:Detailed anatomical knowledge of the NLD is of great importance for safe and successful endonasal surgery. The present study attempts to provide useful surgical guidelines by using anatomic and positional relationships between the NLD and the major surrounding landmarks.

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