Dry eye — MedSys

1. It is two different problems, and most people have both

Tears are not water. They are a three-layer film: an oily outer layer that stops evaporation, a watery middle layer, and a mucin layer that makes the whole thing stick to the eye. Dry eye is what happens when that film fails, and it fails in two ways.

	Evaporative	Aqueous-deficient
What has gone wrong	The oil layer is poor, so tears evaporate too fast	The lacrimal gland is not making enough tear
Usual cause	Meibomian gland dysfunction — blocked oil glands in the eyelid margins	Age, autoimmune disease, medication, radiotherapy
How common	The large majority	Much less common on its own
What actually helps	Heat and lid hygiene first; drops second	Drops, then tear conservation, then anti-inflammatories

This is the distinction the whole chapter turns on. Most dry eye is evaporative, which means the problem is in the eyelids rather than in tear production — and a plain watery artificial tear does not treat blocked oil glands. It relieves the symptom for twenty minutes. That is why people work through six brands of drop, conclude nothing works, and are right.

Not every drop is in that category, and the distinction matters. Lipid-containing drops supplement the layer that is actually missing, and perfluorohexyloctane (section 7) acts directly on evaporation. Those address the mechanism. It is the plain aqueous tear — the default bottle — that only buys twenty minutes.

The other half is that these are not exclusive. Plenty of people have both, and the practical answer is usually to treat the lids and use drops rather than choosing.

And the counterintuitive one, which sends people down the wrong path for years: constantly watering eyes are often dry eyes. A dry, irritated surface triggers a reflex flood of poor-quality tear that runs down the face and does nothing for the surface it came from.

Often, not always. Blocked tear drainage and lid laxity also cause watering, particularly in older people, and they need a different fix entirely — so persistent watering is worth having looked at rather than self-treating as dry eye.

2. Causes, in roughly the order they turn up

Meibomian gland dysfunction and blepharitis — the commonest cause by a distance. Oil thickens, glands block, and over years the glands themselves drop out permanently, which is why treating it early matters more than it sounds.
Demodex mites. They live harmlessly on nearly everyone's skin; an overgrowth on the lash line causes crusting, itch and inflammation, and is thought to account for a large share of anterior blepharitis. The tell is cylindrical dandruff wrapped around the lash base.
Screens. Blink rate falls substantially during concentrated visual work, and blinks become incomplete — the lid does not fully close, so the glands are never properly squeezed. This is the mechanism behind “my eyes are fine until about 3pm”.
Contact lenses — both a cause and the thing dry eye eventually stops you tolerating.
Medication, and this list is longer than most people expect: antihistamines, most antidepressants, beta blockers, diuretics, isotretinoin (which shrinks the meibomian glands directly), some blood pressure drugs, and anticholinergics for bladder symptoms. If your dry eye started within a few months of a new prescription, that is a conversation worth having — not a reason to stop anything.
The preservative in your other eye drops. Benzalkonium chloride is in most multi-dose bottles, including glaucoma drops used daily for years, and it damages the ocular surface. Someone treating glaucoma can be given dry eye by the treatment. Preservative-free versions exist for almost everything. Do not stop a glaucoma drop because your eyes are dry — the pressure will not wait, and NG81 supports preservative-free alternatives for people with ocular surface disease. Ask for one.
Rosacea — ocular involvement is common and frequently missed, because the skin and the eyes get seen by different people.
The menopause transition — dry eye rises sharply around it. See menopause and cognition for the broader pattern of symptoms that get attributed elsewhere.
Sjögren's syndrome and other autoimmune disease — the one to catch. Dry eyes and a persistently dry mouth together is the combination that should prompt testing rather than another bottle of drops.
Laser eye surgery — corneal nerves are cut, and the feedback loop that tells the gland to produce tear is interrupted. Usually improves over months.
Environment — air conditioning, car heaters aimed at the face, wind, low humidity, and aircraft cabins, which run at a humidity lower than most deserts.
Age, and it is not subtle: tear production falls steadily from about forty.

3. When it is not just dry eye

Dry eye is uncomfortable and not dangerous. These are different, and need seeing:

Pain rather than grittiness, especially with light sensitivity — that is not dry eye's usual register
Vision that is blurred and does not clear when you blink
One red eye, particularly with a contact lens history — a corneal ulcer is a same-day problem
Dry eyes with a dry mouth — ask about Sjögren's syndrome. Add fatigue or joint pain and the case is stronger. It is commonest in women in their forties and fifties, is diagnosed years late on average, and the test to ask your GP for is anti-Ro and anti-La antibodies. Years of artificial tears without anyone asking the question is the pattern to avoid
Symptoms that started with a new medicine

4. Lids first — the step people skip

For evaporative dry eye this is the treatment, and drops are the comfort measure alongside it.

Heat, and it has to be hot enough for long enough. Meibum melts around 40–42 °C. A flannel under the hot tap loses that within about a minute, which is why it rarely works — a purpose-made mask that holds temperature for ten minutes is doing a different job. Ten minutes, daily, for at least a month before judging it.
Then massage — gentle pressure along the lid toward the lash line immediately after heating, while the oil is still liquid. Heat without massage leaves the melted oil where it was.
Then clean the lid margin — a dedicated lid wipe or foam, along the lash base rather than the eyelid skin. Baby shampoo is the traditional advice and is now generally discouraged; it strips the surface.
Blink properly. Deliberate full blinks, and a break from the screen — the twenty-twenty-twenty rule exists for this. Unglamorous and free.

5. Drops — what the grades actually mean

The wall of options in a British pharmacy is confusing mostly because the packaging does not explain the two things that matter.

Preservative-free, always, if you are using them more than about four times a day. Benzalkonium chloride is the problem above. Modern preservative-free bottles use a one-way valve and stay usable for months, so the old objection — expensive single-use vials — no longer applies.
Viscosity is the trade-off. Thin drops are comfortable and wear off quickly; thicker ones last longer and blur vision briefly. Sodium hyaluronate at 0.1% is the usual starting strength and 0.2% the step up for moderate or severe symptoms — which is the entire difference between the two products people most often ask about.
Gel or ointment at night if you wake with the worst symptoms, which suggests the lids are not fully closing overnight.
Lipid-containing drops for evaporative disease, which is most people — they supplement the layer that is actually missing.

6. The specific products people ask about

HYLO-Forte and HYLO-Tear. Preservative-free sodium hyaluronate in a valve bottle. The difference is concentration — roughly 0.2% against 0.1% — not quality, so Forte is the step up for more severe symptoms rather than the better product. Sensible, widely used, and it treats the symptom rather than the cause: if your problem is meibomian gland dysfunction, this goes alongside section 4, not instead of it.
TearRestore thermal mask. A reusable self-heating mask with an open-eye design so you can read while wearing it. The manufacturer specifies roughly 42 °C — which is the temperature that matters, and is their figure rather than an independently verified one. The open-eye design is a real advantage for the only reason that counts: the treatment fails mostly because people stop doing it, and ten minutes you can work through gets done. Several brands do this competently; the mechanism is heat, not the badge.
TearRestore OneDrop. A preservative-free nanoemulsion artificial tear launched in the US in February 2026, marketed as covering “all the bases”. Treat that phrase as marketing until it has evidence. At launch there was no published trial, and the clinician quoted in its own launch coverage had not yet used it on patients. But the class is not unproven, and that is the useful distinction. The active ingredient is propylene glycol in a castor-oil nanoemulsion — the same class as existing lipid-based drops, which do have evidence in evaporative disease. So a reader who already owns a bottle should expect it to work about as well as its class does; what is unproven is the claim that it does more. Graded Emerging, and not sold here.

7. The one that inverts the usual story

Miebo — perfluorohexyloctane — was approved by the FDA in May 2023 and described as the first prescription drug that directly targets tear evaporation. It is water-free, preservative-free, used four times a day, and it met both primary endpoints across the GOBI and MOJAVE trials in more than 1,200 patients with meibomian gland dysfunction.

The same molecule is sold in Europe and the UK over the counter, as a medical device, under names including EvoTears and Hycosan Shield.

So the American breakthrough prescription is a British pharmacy purchase, at a fraction of the price, without an appointment. That is the reverse of every other product in this topic, and it is worth knowing before reading US coverage that presents it as something to envy. The regulatory route differs, not the chemistry.

And the balance needs both halves. A device authorisation is a lower evidential bar than a drug approval — easier access here, less scrutiny. But the molecule itself is not lightly evidenced: the FDA approval rested on GOBI and MOJAVE, two randomised trials in more than 1,200 people, both of which met their primary endpoints. The route was lighter; the evidence behind the substance is not.

8. Beyond drops, in the UK

Ciclosporin drops (Ikervis) — an anti-inflammatory for severe disease with corneal damage. NHS specialist prescription, takes weeks to months to work, and stings at first for many people, which is the commonest reason it gets abandoned before it has had a chance.
Punctal plugs — tiny stoppers in the tear drainage holes, keeping the tears you make on the eye longer. Quick, reversible, and the right answer for aqueous-deficient disease specifically. Less useful if the tears you are conserving are poor-quality.
Oral doxycycline or azithromycin — used at low dose for the anti-inflammatory effect on the glands rather than as an antibiotic, particularly with rosacea.
Intense pulsed light (IPL) and thermal pulsation — in-clinic treatments for meibomian gland dysfunction, largely private in the UK, several hundred pounds a course. Reasonable evidence for symptom improvement; not a cure, and the lid routine still has to happen afterwards.
Autologous serum drops — drops made from your own blood serum, for severe disease that has failed everything else. Specialist, and genuinely effective for the small group who need them.
Treat the rosacea, the blepharitis, the sleep apnoea mask leak, or the medication — the cause, where there is one, outperforms everything above.

9. Available in the United States, not here

American coverage names these constantly. As of writing, none is licensed in the UK.

Xiidra (lifitegrast) — an anti-inflammatory drop, twice daily.
Tyrvaya (varenicline nasal spray) — the genuinely novel one. It is sprayed up the nose, not into the eye, and stimulates the nerve pathway that triggers tear production — turning the tap on rather than topping the glass up. Useful for people who cannot manage drops at all.
Cequa and Vevye — ciclosporin in better vehicles than the older formulations, which is mostly a tolerability advance.
Xdemvy (lotilaner) — the first drug approved specifically for Demodex blepharitis. Given how much anterior blepharitis is thought to be mite-driven, this is the gap in UK options most worth watching.

10. Omega-3 did not beat placebo in the best trial

Omega-3 supplements. The DREAM trial randomised 535 people with moderate-to-severe dry eye across 27 centres to 3,000 mg a day of fish-derived omega-3 or a refined olive oil placebo for a year. No significant difference on the primary symptom score or on any objective sign — tear break-up time, staining, Schirmer's. A withdrawal extension found the same.

And the part that matters more than the headline: both groups improved substantially — symptom scores fell by about 14 and 12.5 points. Dry eye fluctuates, regresses to the mean, and responds to attention. That is why testimonials for dry eye remedies are worth so little. Almost anything tested without a control arm will look like it works.

A meta-analysis pooling seventeen trials does report benefit, and the disagreement is mostly about trial quality. This site weights the single large, well-controlled trial over the pooled smaller ones, and says so.

And the comparator objection deserves the same scrutiny this site gave REDUCE-IT. DREAM's placebo was refined olive oil, and it is argued that olive oil is not inert. That is the same class of objection the calculator page takes seriously about mineral oil, and it would be inconsistent to dismiss it here. It does not rescue omega-3 — both arms improved by a similar amount, which is what an active comparator would not usually produce — but it is a real argument. Graded Contested rather than refuted.

11. What is coming

More drugs aimed at the glands rather than the tear, which is the direction the whole field has turned since Miebo — treating the cause of evaporative disease instead of replacing what evaporates.
Demodex-specific treatment reaching the UK, which would change the management of a common and currently under-treated cause.
Neurostimulation beyond the nasal spray, on the same principle of restarting production.

12. What to actually do

Work out which type you have — an optometrist can see the gland openings and measure tear break-up time in a few minutes. Guessing wastes months.
If it is evaporative, do the lid routine — heat, massage, clean — daily for a month before deciding it has failed.
Use preservative-free drops, and step up the concentration rather than the brand if they are not lasting.
Check your medicines, and check what preservative is in any other eye drop you use daily.
Fix the environment — the car vent, the desk fan, the air conditioning.
Ask about Sjögren's if your mouth is dry too.
Do not spend money on omega-3 for this. Spend it on a mask you will use.