Tear evaporation dynamics in normal subjects and subjects with obstructive meibomian gland dysfunction

PURPOSE. To test a newly developed tear evaporimetry system that detects real-time changes in tear evaporation rates and shows the tear film stability in patients with obstructive meibomian gland dysfunction (MGD). METHODS. A ventilated chamber system with high-sensitivity microbalance sensor was used to evaluate tear evaporation. Tear evaporation rates and dynamic changes in them in response to blinking ("flip heights") were measured. Both were compared in 38 eyes of 22 normal subjects and 32 eyes of 21 patients with obstructive MGD, in a prospective case-control study. The relationship between tear evaporation rates and flip heights to meibomian gland orifice obstruction was also analyzed. RESULTS. Changes in tear evaporation rates produced by blinking were detected. The tear evaporation rates in the patients' group were 5.8 ± 2.7(10^-7) g/cm² per second, significantly higher than in normal subjects (4.1 ± 1.4[10^-7] g/cm² per second; P = 0.0008). The flip heights in the obstructive MGD group were 0.58 ± 0.33(10^-7) g/cm² per second, significantly higher than in normal subjects (0.39 ± 0.27[10^-7] g/cm² per second, P = 0.02). The correlations between both tear evaporation rates and flip heights to the meibomian gland orifice obstruction score were statistically significant (P < 0.0001 and P = 0.004, respectively). CONCLUSIONS. This new system was helpful in differentiating MGD patients from normal subjects. These significantly higher evaporation rates and higher flip heights reflect the unstable tear evaporation and may well indicate unstable tear film in patients with obstructive MGD with abnormal evaporative tear loss.