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J. P. McCulley, J. C. Wojtowicz, J. C. Arciniega, E. Mohamed; Meibum Effect on Tear Film Evaporation Over Time. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4635.
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It is generally accepted that evaporation from the tear film is a major factor in dry eye pathophysiology. During ocular blinking meibomian gland secretion (meibum) spread onto the ocular surface to form the lipid layer of the tear film. It is believed that one of its functions is to retard evaporation of the tear film. Therefore, this study was conducted to evaluate the effect of excess meibum in reducing tear film evaporation rate over time.
In a controlled laboratory setting, the effect of expressed meibum on aqueous tear (AT) evaporation was tested in 15 normal subjects without symptoms nor objective findings of dry eye. Evaporative measurements were performed at baseline and following digital expression of both upper and lower lid meibomian glands. Each measurement took 10 minutes to complete. A total of four sequential measurements were taken following digital expression. Subjects were allowed an interval of two minutes in between each measurement to rest. Evaporometer was used at two ranges of relative humidity (RH) 25 to 35% and 35 to 45%.
A statistically significant difference was noted between baseline and the first measurement following digital expression for both RH ranges (p=0.002). There was no statistically significant difference observed between the baseline and the remaining three measurements following digital expression. For the final measurement, a mean value of 0.036 ± 0.011 for the 25-35% range and 0.023 ± 0.011 for the 35-45% range was noted. This was almost the same as the AT baseline measurement: 0.038 ± 0.012 for the 25-35% range (p=0.584) and 0.024 ± 0.007 for the 35-45% range (p=0.438).
Digital meibum expression onto the ocular surface retards evaporation of the tear film, but this effect showed variability over time. A decrease in the AT evaporation rate was noted during the first 12 minutes although this beneficial effect was negligible after 24 minutes. It is concluded that excess meibum has a transient effect on AT evaporation in normal subjects without documented findings of dry eye.
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