Date on Master's Thesis/Doctoral Dissertation

12-2021

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Physiology and Biophysics

Degree Program

Physiology and Biophysics, PhD

Committee Chair

Borchman, Douglas B.

Committee Co-Chair (if applicable)

Joshua, Irving G.

Committee Member

Joshua, Irving G.

Committee Member

Kakar, Sham S.

Committee Member

Roberts, Andrew M.

Author's Keywords

dry eye disease; Meibomian gland dysfunction; spectroscopy; Fiji; meibum; phospholipids

Abstract

It is generally believed that the tear film lipid surface film inhibits the rate of evaporation (Revap) of the underlying tear aqueous. It is also generally believed that changes in the composition of the tear film lipid layer is responsible for an increase in Revap in patients with dry eye. Both of these ideas have never been proven. The purpose of the current studies was to test these ideas. Revap was measured in vitro gravimetrically. Lipid spreading was measured using Raman spectroscopy and microscopy. The influence of the following surface films on the Revap of the sub phase of physiologically buffered saline (PBS) was measured: 1-hydroxyl hydrocarbons, meibum from normal donors and donors with dry eye with and without added phospholipids and phospholipids. The Revap for longer chain 1-hydroxyl hydrocarbons was significantly higher compared with shorter chain 1-hydroxyl hydrocarbons. However, the differences were minor, < 1%. The Revap of tears and PBS were not different. None of the combinations of lipids mentioned above altered Revap more than 1%. A 50% reduction in Revap would be expected if lipid films inhibited Revap. Although surface lipids did not attenuate Revap, phospholipids appeared to facilitate the spreading of meibum. All of the lipid systems studied completely covered the aqueous surface. Meibum from patients with dry eye on the surface aggregated into clusters, but when the same meibum samples were applied to a layer of phospholipids, clustering decreased (66 ± 16 %) significantly. In conclusion, it is unlikely that 1-hydroxyl hydrocarbons can be used to inhibit the Revap of reservoirs. Our data do not support the idea that meibum with or without phospholipids inhibit the Revap of the tears. Perhaps stiff ordered lipids cause the surface lipids to aggregate into ‘islands’ that inhibit the spreading of the tear film which may contribute to tear film instability associated with dry eye symptoms.

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