Why Do I Have Dry Eye and What Can I Do About It?
By Wayne Evardson BSc (Hons) Mc Optom FBDO
This sounds like it should be a very easy question to answer, because you don’t have enough tears! But it turns out that it is actually quite a lot more complicated than that.
The tear film consists of 3 layers:
(1) A layer of mucous which ‘sticks’ the watery tears to the front surface of the eye
(2) A watery layer, which is the majority of the tear volume
(3) A layer of oil (meibum) which sits over the outside surface of the tear film and helps lubricate the lids, but also stops the tears from evaporating so easily
It turns out that most people with dry eye symptoms have a problem with excessive evaporation of the tears, a condition called evaporative dry eye. If we can improve the oily layer then symptoms should improve quite rapidly as the tear film is stabilised under the oil. Dry eyes are more common in contact lens users due to the fact that the lens sits within the tear layer and makes the tear film more unstable already.
The oil is produced by specialist glands within the eyelids called ‘Meibomian Glands’. These lie vertically within both the upper and lower lids and open out in a series of small dots in a line behind the eyelashes. The oil then spreads over the front surface of the tear film. It also protects the skin along the edge of the eyelids preventing the skin from becoming damaged from prolonged contact with the wetness of the tears.
Artificial tear drops help a lot with symptoms as they add more moisture to the eye but to get to the root cause of the dry eye problem we need to improve the oil production of the meibomian glands. When the glands become dysfunctional (and we don’t really know exactly why this happens) the melting point of the oil rises and it no longer flows properly. This means that normal body heat no longer makes the oil liquid but it becomes more paste-like. The glands then become inflamed which makes the problem even worse. Therefore we need to raise the temperature of the glands above the new melting point of the meibum to get everything flowing again. Over time this will make the gland work properly again. There is lots of ongoing research into the causes, prevalence and management of Meibomian Gland Dysfunction and a good review paper was published in 2011.
We are now stocking heated eye masks which should be used twice a day for 4 weeks initially. The masks can be microwaved up to temperature, and then placed over closed eyes for 5 minutes. Once removed, we then massage the lids firmly to move the, now liquid, oil out of the glands. In some cases this also needs to be combined with cleaning of the lid edges and also dry eye drops but your optician will be able to give you individual guidance about this.
Since I have started using these eye masks I have found a big improvement in symptoms for my dry eye sufferers and I am pleased that we can finally deal with the problem, not just improve the symptoms with drops.