SMTube is thin strip with a central  ditch filled with absorber. Scale is printed on the both  side of absorber  to measure the tear volume. Each SMTube is packaged individually in sterile pouch.

When SMTube is applied to the tear meniscus in lateral lower lid of an eye, it absorbs  tears via the capillary action  of absorber  taking effect in the center of the strip. The indicator, placed at the end of the strip, is dissolved  in the absorbed tear fluid. At the end of 5 seconds, the length of the stained tear column is marked and read to quantify the tear meniscus volume.