Meibomian Gland Dysfunction (MGD)

Study Notes

Recognized by ICD codes
Meibomian glands, or glandulae tarsales, are large sebaceous glands present in eyelids that secrete lipids to protect evaporation of the aqueous phase of tear film
There are about 25-40 glands in the human upper eyelid and about 20-30 in the lower eyelid
Each gland consists of clusters of about 10-15 secretory acini that secrete lipid material through small ductules via a central duct at the lid margin
Meibum contains over 100 major individual complex mixture of lipids, over 90 proteins, and electrolytes that contribute to the stability of tear film in health and disease

Chronic, diffuse abnormality of the meibomian glands
Commonly characterized by terminal duct obstruction and/or qualitative/quantitative changes in the glandular secretion
May result in alteration of the tear film, symptoms of eye irritation, clinically apparent inflammation, and ocular surface disease

Underdiagnosed and undertreated disease
Asymptomatic disease is far more common than symptomatic MGD
Estimated that 70% of Americans over the age of 60 have MGD
Prevalence is less among Caucasians when compared to Asians and ranges from 3.5-70% depending on the parameter looked at

Aging
Deficiency of sex hormones (notably androgens)
Systemic conditions (e.g. Sjogren's syndrome, Stevens-Johnson Syndrome, psoriasis, atopy, polycystic ovary syndrome, hypertension)
Ophthalmic factors (e.g. aniridia, chronic blepharitis, contact lens wear, eyelid tattooing, trachoma, Demodex folliculorum infestation)
Use of certain medications (e.g. antibiotics, Isotretinoin, antihistamines, antidepressants, hormone replacement therapy)

Classified based on the final consequence of Dry Eye Diseases (DED) into low delivery and high delivery categories based on the secretion status
Low delivery status further classified into hyposecretory and obstructive conditions
Hyposecretion due to decreased Meibomian gland function from gland atrophy or medications
Obstruction of meibomian glands due to hypertrophy of ductal epithelium and keratinization due to aging, or other factors