Are Your Eyes Dry? Meet Helen.
Series: CBE Departmental Seminars
Location: Elgin Room (E-Quad A224)
Date/Time: Wednesday, December 4, 2013, 4:00 p.m. - 5:00 p.m.
Dry eye, a burny, itchy feeling of dryness and discomfort, is a common malady that infects up to 30 % of the global population. It is especially prevalent in the elderly and women, and in arid, windy climates. During a blink, aqueous tear film is coated and trapped on the cornea, and exposed to a subsaturated air environment. Water evaporates from the tear through a 100-nm lipid-covering layer exuded from the lid meibum glands. We present a periodic-steady description of human tear dynamics that demonstrates how salts concentrate in the tear during the 5-s interblink and how that leads to ocular surface damage. Ameliorating dry eye thus requires understanding and minimizing tear evaporation through a thin duplex-oil film.
By spreading thin oil films of bovine and human meibum and model lipids over the air/water interface in a miniature Langmuir trough, we study in-vitro water-evaporation kinetics for film thicknesses ranging from 100 nm to 100 ?m. Detailed understanding of mass and heat transfer is requisite for obtaining meaningful evaporation kinetics. Contrary to current understanding of the human tear film, however, we find that 100-nm thin films of spread lipid do not slow water evaporation rates enough to prevent increased tear salinity during blinking.
Quantifying the role of the in-vivo lipid layer in controlling tear evaporation in human subjects is extremely challenging, partly because the lipid layer cannot be eliminated or controlled. We design a hand-held in-vivo flow evaporimeter in which the evaporation rate scales linearly with ambient relative humidity and with air velocity to a power index less than unity. Most importantly, we calibrate the new in-vivo evaporimeter using a life-size, anatomically correct mannequin, known as Helen. Preliminary results for selected human subjects (i.e., students) are shown and discussed. The new flow evaporimeter opens many avenues for studying corneal disease and the effects of contact-lens wear.