Purpose: To evaluate the effect of excess meibum on tear
evaporation rate in patients with and without dry eye.
Methods: Eleven healthy subjects and 16 patients with dry eye were
tested. The dry eye group was divided into 2 subgroups: classic
keratoconjunctivitis sicca (KCS) with clear and easily expressed
meibum and KCS with meibomian gland dysfunction (MGD) with
turbid secretions and difficult-to-express meibum. Evaporative
measurements were performed at baseline and after digital expression
of meibomian glands at 12, 24, 36, and 48 minutes. Two ranges of
relative humidity were used, 25% to 35% and 35% to 45%. The data
were expressed as microliters per square centimeter per minute.
Results: An increase in the evaporation rate of the tear film was
noted for all measurements at both relative humidities in the classic
KCS and KCS with MGD groups compared with healthy subjects
(P , 0.05). The average evaporation rates at relative humidities of
25% to 35% and 35% to 45% were 0.056 6 0.016 and 0.040 6 0.008
for the classic KCS group; 0.055 6 0.026 and 0.037 6 0.019 for the
KCS with MGD group and 0.033 6 0.012 and 0.023 6 0.008 for the
healthy group. Also, a decrease in the evaporation rate was observed
in the healthy and KCS with MGD groups between baseline and the
first measurement after digital expression for both relative humidities
(P , 0.05). The classic KCS group did not show any changes after
expression.
Conclusions: Classic KCS and KCS with MGD groups showed an
increase in tear evaporation rates compared with the healthy group.
Aqueous tear evaporation diminished in the healthy and KCS with
MGD groups after expression of meibomian glands. However, this
effect was transient and negligible after the second measurement.