Meibomian gland dysfunction (MGD) is a common eye condition when the meibomian glands in your lids are clogged or have been compromised by chronic inflammation, demodex infestation, long-term use of contact lenses or failure to blink regularly when using digital device use without breaks.
When blocked, the meibomian glands secrete too little or no oil (meibum), which is needed to stabilize your tear film and help avoid your tears from evaporating too quickly.
Meibomian gland dysfunction is considered to be the primary cause of dry eye and is estimated to affect 86% of dry eye patients.
When available, an optometrist can check the structural quality of your meibomian glands by taking pictures of the inside of your lids with a meibographer as shown below.
When the meibomian glands function properly, they will secrete clear oil naturally every time you blink to create a stable tear film.
When blocked or clogged, the meibomian glands secrete little to no oil.  Instead, they will secrete unhealthy crusty, pus or toothpaste-like oil when expressed with forceps.
When left inflamed or clogged for too long, the meibomian glands may atrophy and die off.  At that stage, you will suffer irreversible and permanent dry eye symptoms.