The effect of digital expression of the meibomian glands on the lipid layer of the tear film and evaporation rate

Purpose: To examine the effect of meibomian gland lipid secretions on the evaporation rate and appearance of the human tear film. Methods: We examined 10 volunteer subjects who were not screened for pre-existing ocular pathology. Measurements of the evaporation rate at 30% relative humidity were taken of both right and left eyes prior to and immediately following digital expression of the meibomian glands of the lower lids. Confocal microscopy of the lipid layer of the tear film was also performed on each eye prior to and immediately following digital compression using non-parametric scales: lipid thickness (1 thin, 10 thick), linear pattern (1 linear, 10 nonlinear), debris (1 rare, 10 heavy), pattern stability (1 stable, 10 nonstable), and dry spots (1 few, 10 many). Results: We found that the evaporative rate of both eyes in each subject was significantly reduced following digital expression. The evaporative rate pre-expression was 29.57 ± 9.9 × 10^-7 gms/cm²/sec and post expression increased to 14.75 ± 4.0. The average decrease was 48 ± .12%. Post expression the tear film lipid layer also showed significant changes in appearance. Lipid thickness increased from 3.2 ± 1.5 to 8.0 ± 1.0. The pattern became more linear from 7.8 ± 1.7 to 4.4 ± 3.0. Debris increased from 1.8 ± .87 to 3.6 ± 2.2. The stability improved from 5.0 ± 1.9 to 1.7 ± 0.9. The dry spots did not change 1.0 to 1.0. Conclusions: Meibomian gland expression increases the lipid volume over the tear film, lowers the evaporation rate and can be assessed using tandem scanning confocal microscopy.