Evidence for the major contribution of evaporation to tear film thinning between blinks.

PURPOSE

To determine the contribution of evaporation to the thinning of the precorneal tear film between blinks.

METHODS

The rate of tear film thinning after a blink was measured using spectral interferometry from the right eyes of 37 subjects. Data were obtained under two different conditions: free air and air-tight goggles.

RESULTS

The mean (±SD) tear film thinning rates for subjects was 3.22 ± 4.27 μm/min in free air and -0.16 ± 1.78 μm/min (i.e., a slight but not significant thickening) for the same subjects wearing air-tight goggles; this reduction in thinning rates was significant (P < 0.0001).

CONCLUSIONS

The large reduction in thinning rate caused by wearing goggles indicates that evaporation is the major cause of thinning between blinks. The mean thinning rate in free air is greater than reported evaporation rates; it is argued that the preocular chambers used in evaporimeters restrict movement of air over the tear film and reduce evaporation compared to our free air condition.