The true canalicular angle: a mathematical model.

A mathematical formula that allows for the computation of the true angle between the upper and lower canaliculi using dacryocystograms is described. It was used to determine the true canalicular angle in 33 patients. The mean calculated angle at the 1.0 mm distance was 57.2 degrees +/- 13.0 degrees, and at the 0.5 mm distance was 65.2 degrees +/- 16.2 degrees. The true calculated angle was highly correlated with the angle measured in the Waters view. There was no statistically significant correlation between the right and left sides in the same patient. There was no statistically significant difference between the canalicular angle in males and females, and there was no correlation between canalicular angle and patient's age. A clinical application of this model is discussed.