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E. Knop, N. Knop; Keratinisation and Muco-Cutaneous Junction of the human Lid Margin in Relation to the Meibomian Gland Orifice. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4833.
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Analysis of keratinisation of the human lid margin including the opening and excretory duct of the Meibomian gland may be relevant for the understanding of the onset of Meibomian gland disease (MGD). MDG appears to represent a frequent and potentially underestimated factor in the pathogenesis of dry eye disease.
Conjunctival whole-mount specimens including the lid margin from ten human body donors of older age (average age in the mid seventies) were embedded in paraffin. Serial histological sections were stained with different histological stains (including HE and Masson Goldner's trichrome stain) for investigation of histology and degree of keratinisation.
At the human lid margin the stratified squamous keratinised skin epithelium (epidermis) which also covers most of the free lid margin ended abruptly close to the inner lid margin. This keratinisation typically continued into the initial part of the Meibomian gland and extended in a narrow zone (100-200µm) around the orifice of the gland. Further proximal it was replaced by a para-keratinsed, non-cornified epithelium that represents the muco-cutaneous junction (MCJ). In between the Meibomian orifices the MCJ started slightly further distal in about the middle interconnecting line between the orifices. The initial part of the Meibom excretory duct was typically lined by a stratified squamous keratinised epithelium of varying thickness. The lumen was slightly extended, compared to the rest of the duct and frequently formed a kind of ampulla. Along the terminal around 0,5mm long portion that immediately preceded the orifice, the ductal lumen became narrower. The cornified layer became thicker from the ampulla to the orifice and in the terminal part the cornified layer together with shed luminal keratin lamellae increasingly obstructed the lumen.
The terminal part of the Meibomian gland excretory duct, at least in elderly individuals, is frequently obstructed by a keratinised epithelial cells which may contribute to stasis of Meibom inside the gland and impairment of its proper secretion onto the lid margin. This may contribute to an increased incidence of MGD and dysfunctional tears in the elderly population.
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