A stye, also called a hordeolum, is an infected oil gland of the eyelid. These oil glands are called meibomian glands. They line the upper and lower eyelid margin. When infected, they become red, painful, swollen, and can weigh down the eyelid.
A stye is a synonym for hordeolum. A hordeolum is the term used when the oil gland is acutely infected. After the gland has been infected for approximately a month, the inflamed and infected material inside will change into scar tissue. It is then called a chalazion.
A hordeolum is treated with a combination of antibiotics and steroids. A chalazion typically will require an excision because the scar tissue inside does not respond to medications.
Meibomian glands line the upper and lower eyelid margins. They are located just behind the eyelashes on both the upper and lower eyelids. They secrete the oil layer of the tear film. The oil layer is the most superficial layer of the tear film which coats the eye.
MGD is a condition that is thought to be related to environmental factors, genetic factors, aging, and bacterial overgrowth of the eyelids. It results in the consistency of the gland secretions changing from a normal olive oil consistency to a toothpaste like consistency which is irritating to the eyes. Additionally the glands become atrophic (die). This can result in dry eye disease.