The meibomian glands run along the inner skin of the eyelids with their orifices situated between the eyelashes and and back edge of the eyelids. They are arranged vertically with 30-40 in the upper lid and 20-30 in the lower. Upon blinking, the force created causes expression of oil from the glands. This oil, or meibum, helps prevent evaporation of the thin tear layer and spilling of tears over the eyelid margins. It also interacts with the tear film to enhance the spread of tears by reducing surface tension.
Meibomian Gland Dysfunction (MGD) is a chronic abnormality often characterised by gland obstruction and changes in the qualtiy/quantity of meibum. In a healthy individual the meibum will have an olive oil consistency which progresses to a toothpaste-like consistency in advanced stages of the disease.
MGD results in tear film instability, evaporative dry eye, infections and potential cyst formation. The constant low grade inflammation in MGD eventually leads to keratinisation (blockage) and ‘drop-out’ of the glands. At this stage treatment options become limited. Further, gland drop out causes a physical shift in the remaining glands to a possibly less efficient position within the eyelids.
MGD is often associated with, and can also result from, anterior blepharitis. It is therefore usual to treat both conditions if MGD is confirmed on assessment.
There is a form of MGD called seborrheic blepharitis that results in excessive oil production. This form is commonly associated with seborrheic dermatitis and usually does not involve much obvious inflammation. A common symptom is stinging of the eyes on waking. This is due to a saponification (soap forming) reaction occurring between excess lipids and tear proteins over night.