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Peggy A. Stauffer, Elaine Campbell, Michelle Senchyna, Howard Ketelson; Physical Characterization of Human Meibum using Polarized Light Microscopy. Invest. Ophthalmol. Vis. Sci. 2012;53(14):615.
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Meibum is a lipid rich secretion from glands in the upper and lower eyelids and is a critical component of the tear film. Meibomian Gland Dysfunction is a condition marked by changes to the quality and quantity of meibum which can lead to inflammation and an unstable tear film. The physical characteristics of the meibum may be an important key to understanding how meibum functions as a critical component of the tear film. In order to characterize certain physical characteristics of human meibum, Polarized Light Microscopy (PLM) was used to visualize changes in the crystalline structure as a function of temperature.
After informed consent, meibum samples were collected from the lower lids of six healthy non-dry eyed individuals using a Mastrota paddle and digital pressure. Once expressed, a degreased ocular spud was used to collect a pin-head sized pearl of meibum. Left and right lid samples were pooled and stored neat at room temperature in sealed amber vials. Characterization of inherent crystal structure and melt behavior was accomplished by temperature cycling from 21° to 60°C using PLM on a temperature controlled stage. Visual observations of the recorded images were used to estimate melting point(s) and the size and shape of the crystalline structures.
Using PLM, crystalline structures of various sizes and intensities were observed at 21°C. As temperature was increased, increased fluidity was observed beginning at 32° (+/- 1°) C with subsequent melting of the crystalline structures occurring in 2 phases. The first melt phase began at 38° (+/- 1°) C and the second at 45° (+/- 1°) C. Recrystallization began as the sample was cooled to 35° (+/- 1°) C and was complete by 30°C. Upon recrystallization, crystals formed in a smaller and more uniform pattern than the original samples. Subsequent melting curves demonstrated that the crystalline structure observed in the original sample was unique to those seen upon recrystallization, and changes to the original crystalline structure caused by heating are irreversible.
PLM studies show that human meibum samples have an organized crystalline structure which is sensitive to temperature. The molecular order associated with meibum may be an important parameter to understand in more detail how lipid composition changes and how this may impact tear film stability in MGD dry eye patients.
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