Types of blepharitis
This type of blepharitis is thought to be caused by a bacteria called staphylococcus. This bacterium commonly lives in low numbers on the skin without doing any harm. However, in some people this bacterium causes an infection of the eyelids, resulting in blepharitis.
This type of blepharitis is closely associated with a skin condition called seborrhoeic dermatitis where the affected skin becomes more oily and can become scaly. Seborrhoeic dermatitis typically causes bad dandruff and sometimes rash, commonly on the face and upper body. A type of yeast called Malassezia furfur is involved. This yeast lives in the oil (sebum) of human skin in most adults and usually does no harm. However, in some people the yeast seems to trigger an inflammatory reaction, causing the blepharitis.
This is also known as meibomian gland dysfunction. The tiny meibomian glands in the eyelids lie just behind the eyelashes. You have about 25-30 meibomian glands on each upper and lower eyelid. They make a small amount of oily fluid which comes out on the inside of the eyelids next to the eye. This oily fluid forms the outer layer of the tear film which lubricates the front of the eye. People with meibomian blepharitis are thought to have a problem with their meibomian glands and the fluid they produce which may lead to eyelid inflammation. This also explains why people with meibomian blepharitis often have dry eyes, as the fluid they make may not be adequate to lubricate the eye.