What do my meibomian glands do for my eyes? Why do you have meibomian glands?

The meibomian glands provide the key components of the meibum or oily layer to your tear film to help maintain a balanced, healthy ocular surface.
When meibomian glands are functioning normally, the lipids they secrete reduce the ocular surface tear film watery evaporation and preventing dry eye.
When the glands are reduced, absent or dysfunctional, there can be a very significant effect on the balance and health of the ocular surface. That manifests itself in different ways clinically regarding symptoms and signs.
The clinical signs of meibomian gland dysfunction are variable but are easily seen by an ophthalmologist with binocular magnification by slit lamp examination.
When I examine a patient with symptoms of dry eyes or meibomian gland dysfunction, I mainly look for meibomian gland orifice plugging, eyelid margin foaminess, redness or hyperaemia and telangiectasia along the lid margin and changes in the position of the meibomian gland orifices concerning the mucocutaneous junction.
I then assess the meibomian gland secretions by putting pressure all along the lid margin or the eyelid margin sequentially, and I rate the expressibility and texture of the meibum.
Usually, meibum is clear and very easily expressed, but in meibomian gland dysfunction the meibum becomes more opaque and viscous like and can be quite difficult to express. Often I have to presstovery hard in order to get a little plug to pop out of the meibomian gland orifices and then form thicker turbid meibum to follow.
I also look on the inner aspect of the eyelids to determine meibomian gland drop out. I can do this as well by transillumination through an everted eyelid or by infrared photography.
I also look at the tear film and for ocular surface signs.
I look to see whether there is increased tear evaporation when hyperosmolarity is measured with the tear lab osmolarity machine and I look at the tear breakup time as these can cause irritative symptoms of the ocular surface and eyelids and overlap with dry eye disease.
Meibomian gland dysfunction is a key contributor to the evaporative type of dry eye disease. Tear evaporation occurs because the tear film lipid layer derived from the meibomian glands fails to function correctly to prevent the water evaporation from the optical surface; namely the cornea and the conjunctiva. This protective film layer does not form well over the eye if the meibomian glands are not working correctly and evaporation occurs. If meibum is replaced in the form of oil, a lipid film can be reformed.
In obstructive meibomian gland dysfunction, where there are meibomian gland dropout and poor meibum expression but without noticeable signs of inflammation, there are much higher tear evaporations compared to healthy controls, and the tear evaporation increases proportionally with the severity of the meibomian gland dysfunction.
So, we have concluded that tear evaporation rates correlate closely with the quality of the meibum and the quantity of the meibum on the ocular surface.
Your Meibomian glands and their proper function producing healthy oil, are essential for comfortable eyes and clear vision
I will discuss tear osmolarity in the next blog post.