Abstract
Purpose :
The functions attributed to the Tear Film Lipid Layer (TFLL) include maintaining the lid margin in a hydrophobic state to avoid tear overflow, the lowering of the tear surface tension, and the retardation of evaporation. There has been a number of experimental studies trying to measure the specific influence of the TFLL on evaporation, but the results have been unimpressive and equivocal. In this work, we propose two different systems to quantify differences in evaporation between healthy controls and patients diagnosed with Meibomian disorders.
Methods :
Meibomian lipids were extracted from 10 patients diagnosed with Meibomian gland pathologies and 9 healthy controls. The lipids were used to form a lipid layer of around 100 nm over water. In the first system the evaporation rate was measured by quantifying the volume of pendant drops over time. To better reflect the physical characteristics present on the ocular surface, we developed a new strategy, which measures the evaporation induced by the presence of menisci. In this method, we evaluated the instantaneous speed of colloidal particles in the meniscus formed on the corner of a cuvette.
Results :
Using the pendant drop method we observed that for both cases and controls, the presence of a meibomian lipid layer reduced the evaporation by up to 50%. Nonetheless, no significant difference was noticed between both groups. By tracking particles in a meniscus, we discovered that the evaporation induced by the meniscus was 25% higher in patients with Meibomian disorders, compared to healthy controls.
Conclusions :
Our study adds to the evidence of the role of Meibomian lipids as inhibitors of evaporation. However, most of the experimental investigations rely on the measurement of evaporation that is homogeneous along a surface, which may not be the appropriate configuration for the eye. A more relevant model may be that of evaporation induced by contact lines, such as those found in tear menisci. By employing a novel technique measuring this type of evaporation, we demonstrated a significant increase of the evaporation using lipids films obtained from patients suffering from Meibomian disorders, compared to the healthy controls. This may have implications not only on tear reduction by evaporation, but also on the arise of internal stress, which may lead to the instability of the tear film.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.