There are two types of blepharitis:
- anterior blepharitis - this is when the inflammation affects the outside front edge of your eyelids, where your eyelashes are connected, and
- posterior blepharitis - this is when the inflammation affects the inside front edge of your eyelids, where they come into contact with your eye.
Sometimes, people will experience both types of the condition as the causes of blepharitis are often connected.
Anterior blepharitis
Many cases of anterior blepharitis are caused by a bacterial infection.
Blepharitis that is caused by bacteria is often referred to as staphylococcal blepharitis.
Anterior blepharitis can also occur as a complication of seborrhoeic dermatitis. Seborrhoeic dermatitis is known to cause oily skin, so it is thought that this excess oil can irritate the eyelids and provide a breeding ground for bacteria.
Blepharitis that is caused by seborrhoeic dermatitis is often referred to as seborrhoeic blepharitis.
Posterior blepharitis
Posterior blepharitis is caused when something affects the glands that are found at the rim of your eyelids. These glands are responsible for producing an oily substance that makes up the top layer of your tears. This oily substance is needed to keep your tears in place and help protect your eyes.
Skin conditions such as seborrhoeic dermatitis or rosacea are known to affect how these glands work.
In the case of seborrhoeic dermatitis, the glands produce too much oil, so as in the case of anterior blepharitis; the excess oil is thought to offer a breeding ground to bacteria.
In the case of rosacea, not enough oil is produced. However, this is still a problem, as your eyes are not being properly protected by your tears, so they also become vulnerable to infection.
Around 50% of people with rosacea will experience associated eye symptoms such as redness and irritation. Rosacea that affects the eyes is known as ocular rosacea. Though ocular rosacea is unlikely to develop in people already taking oral antibiotics for rosacea.
Left untreated, ocular rosacea can lead to iritis (inflammation of the iris) or keratitis (inflammation of the cornea).
Blepharitis that is caused by problems with the Meibomian gland is often referred to as Meibomian blepharitis.
Other causes
Less commonly blepharitis can develop as a result of an allergic reaction, or an infestation of lice on the eyelashes.
