The diameter of the nasolacrimal canal measured by computed tomography: gender and racial differences

The incidence of dacryocystorhinostomy surgery among Pacific People is greater than would be expected given their proportion in the population. Some have suggested that racial and sex differences in facial skull dimensions produce narrower nasolacrimal canals and therefore differences in the incidence of primary acquired nasolacrimal duct obstruction (PANDO). We measured the minimum diameter of the canal in those not known to have PANDO.

A retrospective review of the digital computed tomography (CT) database was performed. Minimum diameter of the nasolacrimal canal on axial cuts of a sinus series CT scan was measured. Sex and racial origin were recorded. All series on the database were included. Absence of axial images and pathology distorting the canal excluded a patient. This was carried out in the Department of Radiology and Ophthalmology, Greenlane Medical Centre, Auckland.

A total of 178 CT scans were included. Men had a mean diameter of 3.9 mm (95% confidence interval [95%CI]: 3.8-4.1) versus women 3.6 mm (95%CI: 3.5-3.8) P = 0.01. Both Caucasian and New Zealand Maori had mean diameters of 3.7 mm (95%CI: 3.5-3.9) whereas Pacific People were 4.1 mm (95%CI: 3.9-4.3) P = 0.01.

As in other studies women had narrower canals than men. Surprisingly we found no difference between New Zealand Maori and Caucasian. Unexpected was the larger diameter in Pacific People, as they have a higher incidence of dacryocystorhinostomy surgery. PANDO is likely to be of multifactorial aetiology and nasolacrimal canal diameter may not be a significant factor. Our described method of measuring canal diameter by CT scan is comparable to a cadaver study.