Blepharitis is a common condition, usually developing in middle age but also affecting people of every age from children to the elderly. It is associated with a number of other conditions, including dry eye disease, seborrhoeic dermatitis and rosacea, as well as certain medications, notably isotretinoin. There may be an infection at play, or dysfunction of the meibomian glands, which run along the eyelid margin and secrete the fats that are an important component of tears.

As it is a chronic problem, remissions, relapses and exacerbations are common. Maintenance therapy, as previously described, can significantly reduce the number of relapses and their severity. Complications can include the formation of a meibomian gland cyst (chalazion) or a stye (hordeolum), dry eye syndrome, intolerance to contact lenses and conjunctivitis. Severe and long-standing cases can lead to keratitis – inflammation of the cornea, which can cause ulceration, perforation and decreased visual acuity – and changes to the eyelashes and eyelids, for example, depigmentation, loss or misdirection of the eyelashes, and thickening, ulceration or scarring of the eyelids, which can cause them to turn inwards or outwards (known as entropion and ectropion respectively).