Meibomian gland dysfunction (MGD) affects the small oil glands located along the rims of the eyelids. They produce an essential substance that prevents water evaporation in the tear film. MGD occurs when these glands are not secreting enough oil or secreting poor oil quality. The meibomian glands may also become clogged, causing less oil excretion. As a result, patients may experience burning, dryness, irritation, and itchiness.