Blepharitis is a chronic (longterm) inflammatory condition of the eyelids. It is generally split into anterior and posterior forms, where posterior blepharitis is synomonous with meibomian gland dysfunction (MGD). However, it aids understanding to think of MGD as separate to blepharitis, though they often coexist. Posterior blepharitis then refers to inflammation of the lid wiper, that part of the eyelid that is in contact with, and spreads, the tear film.
Blepharitis is often caused by an overgrowth of the normal bacteria living along the eyelids and base of the lashes. This bacterial overgrowth causes crusting along the eyelids and creates a sticky environment that traps dead skin cells and other debris. The problem is compounded by the fact the eyelids are not usually cleaned properly due to scrunching of the eyes when washing. This can lead to a gradual build up of debris over the years creating an environment in which the bacteria flourish, causing a multitude of irritating symptoms often resulting from the release of bacterial endotoxins. This leads to a chronic inflammation that can affect all the structures of the tear system. This is why anterior blepharitis and MGD often coexist. Chronic inflammation results in a cycle whereby fewer tears, and therefore fewer tear antibodies, are produced resulting in further bacterial proliferation and consequently even more endotoxins so that the condition gets progressively worse.
Though blepharitis has long been thought largely due to bacteria it is now also acknowledged that the demodex mite can be responsible. These live within the eyelash follicle and require a different treatment to the bacterial form.
If blepharitis is confirmed it is important that a cleaning regime be adopted even if there are no symptoms. Irreparable damage is likely to result if left untreated. This is the main reason I do not advocate using artificial tears as the sole treatment. The drops may eliminate any dry eye symptoms but the underlying condition is still there, untreated.