Determination of relative contribution of the superior and inferior canaliculi to the lacrimal drainage system in health using the drop test

Purpose: The aim of this study was to explore the use of the ‘drop test’ as a method of assessing maximal lacrimal outflow capacity, and to measure the relative contribution of the superior and inferior canaliculi to the drainage capacity in normal subjects. Method: The drop test involves instilling measured aliquots of normal saline over 3‐min periods to raise the tear lake medially. Both eyes were assessed; however, for the right lacrimal drainage system only, sequential insertion and then removal of silicone punctal plugs was performed. After each stage the maximal lacrimal drainage capacity was measured. No punctal plugs were placed in the puncta on the left side. Results: Complete data were collected from 20 subjects with a mean age of 35.6 years. The intraclass correlation coefficient for the five left eye readings was 0.98 (CI 0.96−0.99) and the limits of agreement of a single reading were −22.6 to +93.0 µL/3 min. Without intervention, no statistically significant difference was found in the mean lacrimal outflow between the left and right eyes (P = 0.16). A statistically significant reduction in outflow resulted from punctal occlusion (P