A new thread tear test using silicone tubing.

I have already reported the development of a method for measuring tear volume using a cotton thread (No. 82/3, about 0.2 mm in diameter). While this previous testing method proved useful, both in the diagnosis of lacrimal deficiencies, and in cases of slight to medium epiphora, it could not accurately measure the high volume of lacrimation produced in cases of strong epiphora because of the low absorption capacity of the thread. To overcome this shortcoming, I have developed a new system which utilizes a cotton thread enclosed in a soft, calibrated, silicone tubing. In subsequent testing of this new technique, eyes that exhibited a strong epiphora state gave a wetted length of 226.9 +/- 56.0 mm (mean +/- SD) in a 5- to 10-second test. This compares with 41.0 +/- 8.9 mm in tests using thread alone in a 5- to 10-second test (p less than 0.001).