Everything you need to know about what causes meibomian gland dysfunction
As well as ageing and environmental stress from desiccation (called desiccation stress) from low humidity, central heating or air conditioning, there are many different light sources mainly from computer screens, which affects your production of the oil and hence protection of your tear film.
There are also other causes or risk factors. How you blink can affect the distribution of the oil that you are producing over the surface of the eye. If you are looking at a screen (whether it be in cinema, on a computer, laptop, tablet or mobile phone) your blink rate decreases.
Other risk factors for meibomian gland dysfunction include
- tablets and drops you take as medications,
- nutrition, and
- something we call the ‘ocular microbiome’.
The term microbiome is a relatively new medical word, which is a noun describing the microorganisms in a particular environment or part of the body.
We are very dependent on the vast army of microbes to stay alive, and the microbiome protects us against other germs. For instance, your gut breaks down food to release energy and produce vitamins. On the eye, the ocular microbiome it has an important role in protecting against infection and maintaining the health of the front of the eye.
External factors can affect the microbiome, such as environmental desiccating stress that I already mentioned. Also, small factors such as contact lens wear can affect the ocular microbiome. I will talk more about microbiomes a bit later. Meanwhile, here are some of the risk factors for Meibomian Gland Dysfunction (MGD).
1. Hormonal aspects
Androgens and oestrogens have receptors within the meibomian glands. The meibomian glands can respond to their environmental levels of androgen and oestrogen. The meibocytes even contain enzymes, which synthesise and metabolise the sex steroids, androgens and oestrogens within the eccrine gland.
The androgens stimulate meibum secretion and suppress inflammation, whereas oestrogens increase the inflammation in broad terms.
However, androgens also regulate thousands of genes found in the human meibomian glands, including pathways involved with the lipid dynamics and the PPAR or peroxisome proliferator-activated receptor signalling.
Clinically, meibomian gland dysfunction has been described in many androgen-depleted states including individuals who are on anti-androgen agents for instance being treated for benign prostate hypertrophy or prostate cancer, and for individuals with complete androgen insensitivity syndrome and those with Sjögren’s syndrome.
In all of these conditions, there is an alteration in the meibomian gland secretion and lipid profile. For those of you who are men and who may have benign prostatic hypertrophy or suffering from prostate cancer and are on medication, this may well be exacerbating your meibomian gland dysfunction and contributing to worsening of dry eye.
2. Systemic medications
One of the retinoid acids called Accutane, 13-cis-Retinoid acid, is associated with severe atrophy of the meibomian glands. Retinoid Accutane is often taken for severe acne vulgaris, and the retinoic acid binds two nuclear receptors within the meibomian ducts’ epithelium, which causes changes in their gene transcription. That causes the meibomian glands to decrease their volume overall and inhibits maturation of the lipid-laden meibomian acinar cells. The cells get meibum hyposecretion, which then leads to effective evaporation of tears, increase in tear osmolarity and finally dry eye symptoms.
3. Topical medications
Topical medications have also been found to alter meibomian gland dysfunction such as epinephrine, which can cause hyperkeratinisation of the meibomian gland duct epithelium and lead to meibomian gland plugging and dilation. There are also some glaucoma medications such as topical beta-blockers and prostaglandin analogues and carbonic anhydrase inhibitors, which are associated with changes in the meibomian gland morphology, including decreasing the density of the cells which can contribute to dry eyes.
A diet poor in Omega-3 fatty acids o an incorrect ratio of Omega-3 to Omega-6 and -9, can worsen MGD. Taking oral fatty acids as supplements can improve dry eye symptoms and signs, as well as improving the expressibility and quality of the meibum in meibomian gland dysfunction. In particular, Omega-3 fatty acids are associated with beneficial alterations in the lipid profile and decrease in the saturated fatty acid content of meibomian gland secretions.
Taking Omega-3 supplements helps to decrease the ocular surface inflammation measured by the human leukocyte antigen (HLA-DR) in patients with dry eyes and also decreases inflammatory lipid mediator profile and tears. All these are good things. Examples of foods which are rich in Omega-3 fatty acids include fish oil; particularly salmon, mackerel, anchovy, sardine, flaxseed oil and olive oil.
Diet can also affect the downregulation of the PPAR pathway that is seen in meibomian gland dysfunction, which we have already discussed above and in previous blog posts. It is possible to use some drugs to stimulate the PPAR pathway such as Pioglitazone, Thiazolidinedione, Troglitazone, and Rosiglitazone. You can also use dietary supplements that contain conjugated linoleic acid as found in vegetables, fruits, nuts, grains, and seeds and linseed oil, or even docosahexaenoic acid can also be beneficial.
5. Ocular surface microbiome
The meibum contains cholesteryl esters and if there are too many cholesteryl esters in the meibum, this can stimulate the growth of the normal bacteria found on the eyelid margin known as commensal organisms such as staphylococcal aureus. These commensal bacteria have enzymes in them which are lipolytic, in other words, they break down neutral fatty esters releasing triglycerides and free fatty acids into the tear film and alter the composition of the meibum.
Having low-grade Staphylococcal lid margin disease can contribute to your meibomian gland dysfunction. That is one of the reasons you have to clean your eyelids to make sure that fewer commensal organisms are building up, but also to have the correct diet as well, as once the composition of the meibum has been detrimentally altered, you will get dry eyes.
The ocular surface microbiome refers to the normal bacterial life that sits on our lids, lid margins and in our tears which are typically in balance. If there are stimulation and proliferation of Staphylococcus aureus on the lid margin, these bacteria will release products called toxins, as well as the lipase enzymes even in the absence of apparent infection, which can be irritating to the eye and cause symptoms of irritation.
The lipids which are produced are polar lipids and these travel through the tear film in a different way from non-polar or neutral lipids and go through the aqueous layer towards the deeper mucin layer making the tear film hydrophobic and unstable. Also, the break down of triglycerides into the free fatty acids causes and exacerbates hyperkeratinisation within the meibomian glands.
Other infections such as Demodex might have also been associated with meibomian gland dysfunction. Almost a half of meibomian gland dysfunction patients having Demodex presented in one study done in 2011 by Nichols, Foulks, and Bron called the International Workshop on Meibomian Gland Dysfunction: Executive Summary Invest Ophthalmol Vis Sci 2011; 52: 1922 to 1929. Demodex is commonly found in hair follicles in humans and it is believed to have a contribution to meibomian gland dysfunction in some patients.
6. Contact lens wear
Contact lens wear is associated with reduced meibomian gland morphology and function. Contact lens wearers have a higher degree of meibomian gland dropout, and this dropout is irreversible.
They also can have abnormal meibum quality and lid margin abnormalities, which is correlated with the duration of contact lens wear. Hypotheses of why contact lenses drive the pathophysiology of meibomian gland dysfunction include mechanical trauma, plugging from the accumulation of desquamated epithelial cells on the lid margin at the gland orifices, and chronic inflammation or a combination of all of these.
As you can see, there is a lot of knowledge about the precipitating risk factors for MGD and hence ways to improve your eyelids.