Schirmer test and break-up time of tear film in normal subjects.

We examined the precorneal film, the Schirmer test No. 1, and the break-up time tests in 440 healthy young students. There were no statistically significant differences (1) between men and women from the same origin who were brought up in the same environment, (2) between students from different ethnic origins who were brought up in the same environment, and (3) between students of the same origin who were brought up in different environments. Gradual seasonal changes in climatic factors, such as temperature, humidity, visibility, and barometric pressure, seem to have no appreciable effect on the Schirmer test No. 1 or break-up time test.