There are somewhere between 25 and 40 tiny oil glands running vertically through your upper eyelid, and another 20 to 30 in the lower. They're called meibomian glands, after the German physician who described them in the 1660s. Every time you blink properly, they release a small amount of oil onto the edge of the lid, which spreads across the tear film and slows evaporation.
When they stop working well, tears evaporate two or three times faster than they should. That is the mechanism behind most dry eye — not a shortage of tears, but a shortage of the oil that keeps them where they belong.
The awkward part is that these glands can be quietly deteriorating for years before anyone notices. By the time symptoms show up, some of the gland tissue may already be gone, and gland tissue that has atrophied does not grow back. That's the single most important thing to understand about MGD, and the reason it's worth taking seriously earlier than most people do.
What goes wrong
Two things, usually at the same time.
The openings block. The gland orifices sit along the lid margin, just behind your lashes. Over time they can become capped with hardened oil, keratin and debris. Nothing gets out.
The oil itself changes. Healthy meibum is clear and runny at body temperature, roughly the consistency of olive oil. In MGD it thickens. It becomes cloudy, then granular, then in advanced cases something close to toothpaste. Thick oil doesn't flow through narrow ducts, which worsens the blockage, which raises pressure inside the gland, which damages the cells lining it.
If the blockage persists, the gland dilates, the tissue atrophies, and eventually it drops out altogether. On a meibography scan — an infrared image of the lids — you can see this directly. Healthy glands look like a neat row of vertical stripes. In advanced MGD there are gaps, shortened stubs and truncated ends.
How to tell if you have it
Some of the signs are visible in a mirror. Pull your lower lid down gently in good light and look at the margin, the strip of skin just behind the lashes:
• Small white or yellow caps over the gland openings
• Fine red blood vessels crossing the lid margin towards the lashes
• A thickened, irregular or notched lid edge
• Foam or froth collecting at the outer corner or along the lid margin
• Crusting at the lash bases, which points to blepharitis, a frequent travelling companion of MGD
Symptom-wise, MGD tends to produce:
• Eyes that feel worse as the day goes on
• Grittiness, burning, or a sensation of something in the eye
• Blurred vision that clears when you blink hard
• Reduced contact lens comfort
• Watery eyes, for the reflex-tearing reasons covered in the dry eye article
• Recurrent styes or chalazia, which are essentially blocked glands that have become inflamed or infected
Quite a lot of people with clear gland dropout on imaging report no symptoms at all. That's part of why routine lid margin examination matters even when nothing hurts.
Why it happens
Blinking, or the lack of it. Every complete blink squeezes the glands. Incomplete blinks — where the upper lid comes down most of the way but doesn't fully meet the lower — don't. Screen use produces a lot of incomplete blinks. So does reading, driving and anything else requiring sustained concentration. Over years, poor blinking means poor gland turnover.
Age. Gland dropout increases steadily from around the fourth decade.
Skin conditions. Rosacea and seborrhoeic dermatitis are strongly associated. If you flush easily, have visible facial redness, or have a history of dandruff and scaly eyebrows, the lid margins are usually involved too.
Demodex mites. These live in hair follicles and are more common with age. In larger numbers they cause a characteristic sleeve of debris around the lash base and can inflame the glands. They need targeted treatment, not just standard lid hygiene.
Hormonal changes. Androgens influence gland function, which is one reason MGD becomes more common around and after the menopause.
Isotretinoin. Effective for acne, but it shrinks sebaceous glands throughout the body, including the meibomian glands. The effect can outlast the course of treatment.
Contact lens wear. Long-term wear is associated with gland dropout, although the mechanism is still debated.
Eye makeup on the waterline. Applying eyeliner or kohl to the inner lid margin puts pigment directly over the gland openings. It's a genuine risk factor, and one that's easy to change — apply outside the lash line instead.
Treatment: heat is the foundation
Meibum needs to be warmed before it will move. The melting point of abnormal meibum is higher than normal meibum, which is why casual attempts at warm compresses so often do nothing.
To actually work, a compress needs to hold the inner lid surface at roughly 40°C for around eight to ten minutes. A flannel run under the hot tap loses most of its heat within 90 seconds. If you're using a flannel, you'll need to re-wet it every couple of minutes, and honestly, most people give up.
A reusable microwaveable eye mask filled with flax or silica beads is a far better bet. Heat it per the instructions, check the temperature against the inside of your wrist first, and keep it on for the full duration. Comfortably warm, never hot. Burning the eyelid skin is a real risk and the skin there is the thinnest on the body.
Then massage. Heat alone softens the oil; something has to move it. With clean hands and eyes closed, use a fingertip to sweep the upper lid downwards towards the lashes, and the lower lid upwards towards the lashes. Firm but gentle, about ten strokes each. Always towards the lash line — that's the direction the ducts run.
Then clean. Wipe along the lash base and lid margin with a dedicated lid wipe or a foam cleanser on a cotton pad. This clears away the softened oil and debris you've just released. Diluted baby shampoo was the standard advice for years and still gets recommended, but purpose-made lid cleansers are gentler on the ocular surface and generally better tolerated.
Do all three, in that order, once or twice daily. Expect to keep going for at least six to eight weeks before judging the results, and expect to continue in some form indefinitely. MGD comes back when treatment stops.
When home treatment isn't enough
In-clinic gland expression. A clinician warms the lids and applies controlled pressure with forceps or paddles to clear blocked ducts directly. More effective than anything you can do at home, and often used to reset things before you take over with maintenance.
Thermal pulsation systems. Devices such as LipiFlow apply heat to the inner lid surface while massaging from the outside, in a single 12-minute treatment. Results typically last somewhere between nine and eighteen months.
Intense pulsed light (IPL). Originally a dermatology treatment for rosacea, now widely used for MGD. Pulses of filtered light applied to the cheeks and lower lids reduce inflammation, close abnormal blood vessels and appear to improve meibum quality. Usually a course of three or four sessions a few weeks apart. The evidence base has strengthened considerably, though it works better for some patients than others and it isn't suitable for all skin types.
Topical azithromycin, which has both antibacterial and anti-inflammatory effects on the lid margin.
Low-dose oral doxycycline or lymecycline. Prescribed at anti-inflammatory rather than antibiotic doses, typically for several weeks to months. Not suitable in pregnancy or for children, and it increases sun sensitivity.
Demodex-directed treatment if mites are found, usually a lid cleanser containing terpinen-4-ol, the active component of tea tree oil. Neat tea tree oil should never go near the eye.
Blinking retraining. A structured programme of conscious complete blinks, sometimes with an app or reminder, aimed at the underlying mechanical problem rather than its consequences.
The point about acting early
Most chronic eye conditions give you some warning. MGD often doesn't. Gland dropout accumulates silently, and the treatments above are far better at preserving remaining glands than at rescuing lost ones.
So if you're in your thirties or forties, spend a lot of time on screens, and your eyes get tired by the evening, that's worth mentioning at your next sight test rather than filing under normal. Ask whether your lid margins have been examined and whether meibography is available. It takes a couple of minutes and it tells you where you stand.
The glands you protect now are the ones you'll still have in twenty years.