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C. A. Blackie, D. R. Korb; Meibomian Gland Expression: Forces of Expression, Types of Secretion and the Limitation of Resulting Pain. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3385.
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Meibomian gland expression (MGE) is required for diagnosis of the presence or absence of individual meibomian gland (MG) secretion, the quality of the secretion, and the status of the MG excretory pathways. MG expression is the only method to determine the functionality of an individual MG. Instrumentation for standardized diagnostic expression utilizing 0.3PSI was introduced in 2008, and further custom instrumentation to exert pressures from 1.0 to 150 PSI was developed to determine the amount of force required to: (1) determine whether individual glands are functional when evaluated with forces approximating those of forceful blinking, (2) determine whether non-functional individual glands have the potential to secrete, (3) determine the forces required for therapeutic expression to treat obstructive MGD.
Expression pressures from in the range of 1 - 333 g/mm2 (0.3 - 100 PSI) were applied for a standardized time of 15 seconds to evaluate the forces required for the aforementioned three forms of expression, and to study the nature of the expressed secreta resulting from a particular force.
The force to evaluate gland functionality is 1 - 2 g/mm2 (~ 0.3 - 0.6 PSI); to determine the potential to secrete 3 - 204 g/mm2 (~ 0.9 - 60 PSI), and 4 - 275 g/mm2 (~ 1.2 - 80 PSI) for therapeutic expression. The maximum force which could be tolerated, despite topical anesthesia, was limited by the subjective pain response, and varied from 15 - 275 g/mm2 (~ 5 - 80 PSI).
Determination of MG functionality requires the evaluation of MG expressibility. The use of an instrument providing a standardized force for diagnostic expression is desirable, if not mandatory, for evaluation of MG function. Forces of significant magnitude are required for therapeutic expression, with pain being the limiting factor.
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