Doctors may press on the eye lids to determine if the meibomian glands are secreting meibum (confirming the patency of the glands), or if they are blocked. When the eye lids are gently pressed, healthy meibomian glands will secrete a small amount of meibum that will appear as a clear drop on the eye lid margin, at the opening of the meibomian gland. There should only be the sensation of pressure. If there is tenderness, the meibomian glands may be blocked or diseased, a sign of meibomian gland dysfunction (MGD).
Healthy meibomian glands secrete adequate quantities of meibum. The meibum secreted by healthy glands is clear, colorless, and contains no particulate matter. Unhealthy meibomian glands secrete meibum that may be amber-colored, opaque, thick and pasty like toothpaste, or contain particulate matter. Unhealthy meibomian glands may secrete little meibum.
If no meibum is secreted under gentle pressure, this is an indication of drop out or obstruction. The gland may be fully obstructed or partially obstructed. Or the gland may dead or dormant. It is not uncommon for obstruction to occur at any point along the length of the gland, not just at the opening, or for there to be more than a single point of obstruction.
Sometimes when pressure is applied to the glands and some oil is secreted it is assumed that the glands are functioning. But in reality the oil may be flowing only from the part of the gland nearest the opening. This gives the appearance of a healthy or functioning gland while deeper in the gland there may be obstruction which restricts the flow of meibum, leading to misdiagnosis.
Fibrous tissue bands that encircle the gland (periductal fibrosis) may be found to be the cause of obstruction as well as hardened or stagnant meibum.
Comparison of meibomian gland loss and expressed meibum grade between the upper and lower eyelids in patients with obstructive meibomian gland dysfunction
Eom Y, Choi KE, Kang SY, Lee HK, Kim HM, Song JS.
2014 May;33(5):448-52. doi: 10.1097/ICO.0000000000000092.
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Meibum Color and Free Fatty Acid Composition in Patients With Meibomian Gland Dysfunction
Arita R, Mori N, Shirakawa R, Asai K, Imanaka T, Fukano Y, Nakamura M, Amano S.
Investigative ophthalmology & visual science
2015 Jul;56(8):4403-12. doi: 10.1167/iovs.14-16254.
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