Secretion, meibomian gland

Etiology. Meibomian gland secretions are responsible for the lipid component of the precorneal tear film. The chemical composition of meibum and/or the lipase action of the normal lid bacteria is thought to contribute to or cause blepharitis and in many cases the dry eye that accompanies it. The composition of meibum has been found to be different in normal and blepharitis patients, and there is a distinct difference between the types of MGD as well. Most studies of lid flora in bacterial blepharitis cases did not find any appreciable isolates from meibum that were not found as normal flora on the lids, therefore disproving the theory that the meibomian glands act as a bacterial reservoir. 

Signs of meibomitis include inspissated orifices of the meibomian glands (Figure 23-8A), cloudy or thickened yellow-white meibomian secretions on gland expression, frothy tear film (Figure 23-85), hyperemia, mild papillary conjunctivitis, and thickened rounded eyelid margins. SPK of the cornea and conjunctiva in the inter-palpebral space is associated with an unstable tear film evidenced by a markedly reduced tear breakup time. 

An internal hordeolum is a localized staphylococcal infection of the meibomian glands. The infection may result from blockage of the gland and is foimd more frequently in the upper lid. A specific change in meibomian gland secretion has been linked to internal hordeolum formation. 

Figure 24-8 Meibomian gland disease. Note caps or domes over meibomian orifices. These can be translucent, as in this case, or opaque,indicating a more severe solidification of meibomian secretions.

Evaporative dysfunction is caused by a reduction in the lipid layer of the tear film. Most often, this condition is caused by MGD or blepharitis. MGD is traditionally conceptualized as a triad of meibomianitis (stagnated secretions within the meibomian glands), meibomian seborrhea (overabundance of meibomian secretions into the tear film), and seborrheic blepharitis (oily debris visible on the eyelashes and ocular adnexal surfeces). Additionally, we have become increasingly aware of the influence of male hormones, or androgens, on the health of the meibomian glands. Clinically significant androgen deficiency, which naturally occurs in women of menopausal age and men in... 

Certain abnormal meibomian gland secretion/gland atrophy, increased tear film osmolarity, decreased tolerance to CL, ocular discomfort, blepharoconjunctivitis, keratitis, corneal opacities, decreased vision, photophobia decreased dark adaptation, myopia intracranial hypertension (IH). 

Similar to mouse models that lack the acyl-CoA cholesterol acyltransferase-1, diacyl-glycerol acyltransferase-1, and ElovlS genes, Scdl mice exhibit cutaneous abnormalities with atrophic sebaceous glands and narrow eye fissure with atrophic meibomian glands, suggesting an important role of MUFA in skin and eyelid homeostasis. The major function of sebaceous and meibomian glands is to secrete lipid complex lubricants, termed sebum and mebum, respectively. These lubricants contain wax esters, TGs, and cholesteryl esters, and prevent the evaporation of moisture from the skin and the eyeball. 

The lipid composition is kept within physiological limits by androgens [17]. The decrease of their secretion in elderly people is one of the reasons for development of dry eye syndrome. Patients with Meibomian gland dysfunction show a high tear film evaporation rate and a high tear osmolality [18, 19]. 

Meibomian glands are specialized glatMls that secrete a sebaceous substance. 

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