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Tear Film and Tear Glands: Layers, Function and Tear Duct Eye Surgery
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Tear film (noun): the tear film is the thin, moist coating that covers the front of the eye, made of an oily lipid layer, a watery aqueous layer and a mucin layer. It is produced by the tear glands: the lacrimal gland and accessory glands (water), the meibomian glands in the eyelids (oil) and the goblet cells of the conjunctiva (mucin). It keeps the cornea smooth, clear and protected, and tears then drain through the tear ducts into the nose. When those ducts block, tear duct eye surgery can create a new drainage route.
Tear film and tear glands: key facts
- Where it is
- A thin film over the cornea and the white of the eye (the conjunctiva)
- Thickness
- About 2–5.5 micrometres over the cornea; the lipid layer is only about 40 nanometres thick on average
- Volume
- About 8 microlitres (± 3) of tears on the eye at any moment
- Turnover
- Roughly 16% of the tear volume is renewed every minute (± 5%)
- Main producers
- Lacrimal gland (water), meibomian glands (oil), goblet cells and surface cells (mucins)
- Drainage
- Puncta, canaliculi, lacrimal sac and nasolacrimal duct into the nose; about 80–90% of drainage uses the lower canaliculus
- Common problems
- Dry eye disease, meibomian gland dysfunction, watering eyes, blocked tear duct
- Specialist
- Ophthalmologist; for eyelid and tear duct problems an oculoplastic surgeon. At Laser Istanbul Clinic, eyelid and oculoplastic surgery is led by Prof. Dr. Ahmet Satıcı
What is the tear film? Tear film anatomy
The tear film is not just "water on the eye". It is a thin, constantly renewed layer, only 2–5.5 micrometres thick over the cornea (a fraction of the width of a human hair), that acts as the eye's first optical surface. The 2017 TFOS DEWS II Tear Film Report, an international expert review of the tear film, describes it as a single dynamic unit with different compartments.
What the tear film does (tear film function):
It is the eye's first refracting surface
Light passes through the tear film before it reaches the cornea, so a smooth, stable film is needed for sharp vision.
It protects and moisturises the cornea,
which has no blood vessels and relies on tears for much of its comfort and health.
It provides lubrication, some nutrients and the right salt balance
(osmolarity) for the surface cells.
It defends against infection
with antimicrobial proteins and antibodies such as lysozyme, lactoferrin and secretory IgA.
It washes away dust and debris
with every blink.
Layers of the tear film: layers, glands and thickness
How many layers does the tear film have? The classic textbook model has three: lipid, aqueous and mucin. Researchers call it "a considerable simplification" of a more mixed, dynamic structure, but it remains the clearest way to understand tear film layers and functions. From the outside in:
| Layer (outer to inner) | Made by | What it does | Thickness |
|---|---|---|---|
| Lipid layer (oily) | Meibomian glands in the eyelid edges | Slows evaporation and stops tears spilling over the lid; keeps the surface smooth | About 40 nm on average (reported range 15–157 nm) |
| Aqueous layer (watery, the bulk of the tear film) | Main lacrimal gland, with the accessory glands of Krause and Wolfring and a smaller share from the conjunctiva | Moisturises, nourishes, carries antibodies and antimicrobial proteins, washes away debris | Makes up most of the 2–5.5 µm total |
| Mucin layer (glycocalyx and gel) | Goblet cells of the conjunctiva and the surface cells of the cornea and conjunctiva | Helps the watery tears spread evenly and stick to the eye's surface; transmembrane mucins extend up to about 0.5 µm into the tear film | Up to about 0.5 µm |
Tear film diagram (text version): from the air down to the eye: air → lipid layer → aqueous layer (with mucins mixed through it) → mucin layer / glycocalyx → corneal and conjunctival surface cells. {{Tear film diagram image: layers labelled, with the glands that make each layer}}
What is the lipid layer of the tear film?
The lipid layer of the tear film is the thin, oily outer coat that sits on top of the watery layer. It comes almost entirely from the meibomian glands, a row of tiny oil glands inside the upper and lower eyelids, and it works like a seal that slows evaporation. When the glands are blocked or the oil is poor in quality, the tears evaporate too quickly. This is called meibomian gland dysfunction, a leading cause of evaporative dry eye.
Which glands make the tear film? Tear film layers and glands
- Main lacrimal gland: sits in the upper outer part of the eye socket, about 20 mm long and 12 mm wide, and makes most of the watery tear volume, including most of the "reflex" tears you produce when the eye is irritated or you cry. It also secretes antibodies, lysozyme and lactoferrin.
- Accessory lacrimal glands (Krause and Wolfring): about 20 glands of Krause sit in the upper conjunctival fold, with roughly half that number in the lower fold. Together the accessory glands supply about 10% of the lacrimal secretory mass and are thought to give a steady, everyday "basal" supply.
- Meibomian glands: make the oily layer.
- Goblet cells: scattered across the conjunctiva, they make mucin.
The glands work together as one system, called the lacrimal functional unit, controlled by nerves from the cornea and the surface of the eye. Sensors in the cornea detect drying or irritation and trigger tear secretion through the facial (parasympathetic) nerve. This is also why surgery that cuts corneal nerves can reduce tear production for a time.
How do tears drain? The tear duct system
Tears do not simply disappear. After spreading across the eye with each blink they drain through a small channel network, and a smaller share evaporates (an estimated 10–20%):
- Puncta: two tiny openings (about 0.3 mm wide), one on the inner edge of each eyelid.
- Canaliculi: narrow tubes about 8–10 mm long that carry tears from the puncta; the lower one handles about 80–90% of drainage.
- Lacrimal sac: a small reservoir beside the nose, about 12–15 mm tall.
- Nasolacrimal duct: the "tear duct" itself, leading into the nose. This is why your nose runs when you cry.
Blinking powers the system: when the lids close, the muscle around the eye squeezes tears towards the sac, and when they open the sac pushes tears down the duct. If any part of this route is narrowed or blocked, tears back up and the eye waters.
Tear film problems: dry eye, watering eyes and blocked tear ducts
Dry eye disease
In 2017 the TFOS DEWS II report defined dry eye as a multifactorial disease of the ocular surface in which the tear film loses its balance, with symptoms, tear instability, increased salt concentration (hyperosmolarity), inflammation and nerve changes all playing a part. It happens when the eyes do not make enough tears, make the wrong type, or the tears evaporate too fast. Estimates of how common it is vary widely, from about 5% to 50% of people depending on the population and the definition.
Typical symptoms are stinging, burning, grittiness, redness, light sensitivity, blurred vision and, paradoxically, watering eyes. Risk factors listed by the American Academy of Ophthalmology and the US National Eye Institute include age over 50, being female (especially after the menopause), contact lenses, long screen use, dry or windy surroundings, autoimmune conditions such as Sjögren's syndrome, eyelid disease such as blepharitis, and some medicines (including antihistamines, beta-blockers and antidepressants).
Meibomian gland dysfunction (MGD)
MGD is blockage or poor function of the oil glands in the eyelids. It leads to an unstable lipid layer and evaporative dry eye. It is common, often painless, and is a frequent reason that "dry" eyes keep coming back.
Watering eyes (epiphora)
Watering eyes can look like the opposite of dry eye, but the two are linked. An irritated, dry surface can trigger reflex tearing, which overwhelms the drainage system. The NHS lists cold or wind, allergies, infections, eyelid problems such as turned-in or drooping lids, dry eye and blocked tear ducts among the causes of watery eyes.
Blocked tear duct
In a blocked tear duct (nasolacrimal duct obstruction) tears cannot drain, causing constant watering, sticky discharge and sometimes repeated infections of the sac. In adults, the American Academy of Ophthalmology notes that obstruction can follow infection, swelling, injury or a tumour. Newborns often have a thin membrane at the lower end of the duct; estimates put it at about 5% to 20% of babies, and about 90% clear up on their own within the first year.
How is the tear film tested?
A tear film test is quick and usually painless. Your eye doctor chooses from:
- Slit-lamp examination: a microscope check of the lids, the meibomian gland openings and the cornea.
- Tear break-up time (TBUT): a drop of fluorescein dye is placed in the eye and the doctor times how long the tear film stays intact after a blink. A normal value is around 10 seconds; 5 seconds or less is a typical dry eye cut-off, though it varies by clinic and region.
- Schirmer test: a thin strip of paper hooked over the lower eyelid for a few minutes measures how much tear fluid the eye produces. A wetting of 5 mm or less is a commonly used cut-off for dry eye; the test is most helpful in severe watery-tear deficiency.
- Ocular surface staining: dyes show areas of damage on the cornea and conjunctiva.
- Tear osmolarity: a sample is analysed for salt concentration. Normal tears average about 302 mOsm/L, and 308 mOsm/L or higher is a commonly used threshold for dry eye.
- Meibography and lipid layer imaging: photographs of the meibomian glands, and interferometry that measures the lipid layer.
- Dye disappearance test and syringing: for watery eyes, the doctor checks whether tears drain; in children, retained dye after 5 minutes suggests a blocked duct, and in adults the duct can be flushed with saline to find the blockage.
Treatment: improving the tear film
How to increase tear production in eyes naturally
There is no proven natural way to make a diseased lacrimal gland produce more water, but several steps protect the tears you have and are the first line of care recommended by the NHS and the American Academy of Ophthalmology:
- Take regular screen breaks and blink fully; place the screen slightly below eye level.
- Clean the eyelids daily and use a warm compress to loosen blocked meibomian gland oil.
- Use a humidifier and avoid smoke, wind and direct air-conditioning.
- Wear glasses instead of contact lenses for part of the day.
- Use over-the-counter artificial tears.
- Ask your doctor whether any medicine you take dries the eyes. The National Eye Institute lists lack of vitamin A and omega-3 fatty acids as dry eye risk factors, so discuss diet or supplements with a doctor before starting.
If that is not enough
| Step | What it is |
|---|---|
| Prescription drops | Anti-inflammatory drops such as cyclosporine or lifitegrast; short courses of steroid drops |
| Punctal plugs | Tiny plugs in the puncta that keep tears on the eye longer |
| Treatments for meibomian glands | Thermal pulsation (LipiFlow), intense pulsed light, antibiotic courses for chronic blepharitis |
| Treating eyelid problems | Lids that turn in or out, or do not close fully, can be corrected surgically |
| Surgery to close the tear drainage | A rare option for severe dry eye |
Tear duct eye surgery: when is it needed?
Tear duct eye surgery means a procedure on the tear drainage system to treat persistent watering eyes caused by a blockage. It is considered when the cause is a blocked drainage route rather than a dry eye surface, and when simpler steps have not solved it. Your doctor first finds where the blockage is, because the right operation depends on it.
| Procedure | What it is | Typically used for | Reported success |
|---|---|---|---|
| Probing and syringing | A fine instrument or saline flush opens the duct | Newborns and children; limited benefit in adults | Probing in children: 70–97%; in adults, about 50% |
| Silicone tube (intubation) or balloon dilation | A soft tube or balloon keeps a narrowed duct open | Partial blockage, narrowed canaliculi | About 53–68% |
| Punctoplasty | Opens a narrowed punctum | Punctal stenosis (often from chronic blepharitis) | Functional success 76–96% in reported series |
| Dacryocystorhinostomy (DCR) | Creates a new drainage route from the lacrimal sac into the nose by removing a small piece of bone next to it | Blockage of the nasolacrimal duct in adults; repeated infection of the sac | External DCR up to 90–95%; endoscopic DCR 84–94% in systematic reviews |
| Conjunctivodacryocystorhinostomy (Lester Jones tube) | A glass tube carries tears from the eye corner to the nose | When the canaliculi are blocked or absent | Specialist option |
External or endoscopic DCR? External DCR uses a small cut beside the nose and leaves a skin scar. Endoscopic (endonasal) DCR goes through the nose with a camera, so there is no skin scar. Both are usually performed under sedation or general anaesthesia and most patients go home the same day. Silicone tubes, if used, are typically removed after 4–8 weeks. Risks include bleeding, infection, scarring that closes the new opening and persistent watering; serious complications are uncommon.
Treatment with us: Prof. Dr. Ahmet Satıcı's practice includes eyelid and oculoplastic surgery. {{Tear duct surgery (DCR, intubation): confirm whether Laser Istanbul Clinic offers it, who performs it, and wording for this section}}. If you have watery eyes, send us your reports first: a free review tells you whether your problem is on the surface of the eye, in the eyelids or in the tear duct, and which specialist you need.
Tear film and eye surgery: laser and cataract
Surgery on the front of the eye affects the tear film, which is why dry eye is checked before any laser treatment. The American Academy of Ophthalmology notes that almost everyone has some dry eyes and changing vision after LASIK, usually fading within a month, though for some people it takes longer; severe dry eye is a reason not to have LASIK. Laser surgery cuts some corneal nerves, which reduces the signal that triggers tears while they regrow. Cataract surgery has a similar effect: in one study, 9.8% of patients reported dry eye symptoms a week after surgery and symptoms improved over three months.
At Laser Istanbul Clinic, your surgeon checks your tear film and the surface of your eye as part of the pre-operative examination, and existing dry eye is treated before laser surgery is planned. Laser surgery is not for everyone; suitability depends on your eyes.
When to see a doctor about your tears
Seek urgent care (same day) if you have:
- sudden vision changes or severe eye pain
- a very red, painful eye with light sensitivity, or a red eye in a contact lens wearer
- a chemical splash or an injury to the eye
- a hot, red, tender swelling next to the nose or by the inner corner of the eye (possible infection of the tear sac)
Book an appointment if you have:
- dry, gritty or burning eyes that continue after several weeks of self-care
- watering eyes that interfere with daily life, or one eye that waters constantly
- repeated sticky discharge or repeated eye infections on one side
- eyelids that turn in, turn out or droop
- a dry mouth and dry eyes together, which can signal Sjögren's syndrome
- plans for laser or cataract surgery and a history of dry eye
Frequently asked questions
The tear film is the thin layer of liquid covering the front of the eye. It has an oily lipid layer, a watery aqueous layer and a mucin layer, and it keeps the cornea smooth, protected and hydrated.
There are three layers in the classic model: the outer lipid layer made by the meibomian glands, the middle aqueous layer made mainly by the lacrimal glands and the inner mucin layer made by goblet cells and surface cells. Researchers describe this as a simplification, because the layers mix and function as one dynamic unit.
The tear film is about 2–5.5 micrometres thick over the cornea. The lipid layer is much thinner, about 40 nanometres on average.
It provides a smooth surface for light to enter the eye, protects and moisturises the cornea, supplies nutrients and defends against infection. Every blink spreads it fresh over the eye.
The main lacrimal gland and smaller accessory glands make the watery layer, the meibomian glands in the eyelids make the oily layer, and goblet cells in the conjunctiva make mucin.
There is no proven natural way to increase production from a damaged gland. You can protect your tears by blinking fully, taking screen breaks, warming and cleaning the eyelids, using a humidifier and using artificial tears. See an eye doctor if dryness persists for more than a few weeks.
It is surgery to restore drainage of tears when the tear duct is blocked. The most common operation in adults is dacryocystorhinostomy (DCR), which creates a new pathway between the lacrimal sac and the nose. Reported success is roughly 84–95% depending on the technique.
DCR is performed under sedation or general anaesthesia, so you do not feel the operation, and most people go home the same day. A week of rest and avoiding heavy lifting is typical, and silicone tubes, if placed, are usually removed after 4–8 weeks. Your surgeon will give you personal advice.
Yes. When the surface of the eye is dry or irritated, the glands can overproduce watery reflex tears, which spill over the lids. This is one reason a dry eye can look like a watering eye.
See a doctor if your eyes are painful, red or your vision changes, if dryness or watering continues for more than a few weeks, or if you have repeated infections or a swelling by the nose. Seek urgent care for sudden vision loss or severe pain.
Sources for the facts on this page
- Willcox MDP, et al. TFOS DEWS II Tear Film Report. The Ocular Surface 2017;15(3):366–403. https://pmc.ncbi.nlm.nih.gov/articles/PMC6035753/ (structure, thickness 2–5.5 µm, lipid layer about 40 nm, volume 8 ± 3 µl, turnover 16 ± 5%/min, glands, functions)
- Craig JP, et al. TFOS DEWS II Definition and Classification Report. The Ocular Surface 2017;15(3):276–283. PubMed: https://pubmed.ncbi.nlm.nih.gov/28736335/ (definition of dry eye; wording checked via the review at https://pmc.ncbi.nlm.nih.gov/articles/PMC7730816/, which also gives TBUT ≤5 s and Schirmer ≤5 mm cut-offs)
- American Academy of Ophthalmology. Dry Eye. https://www.aao.org/eye-health/diseases/what-is-dry-eye
- American Academy of Ophthalmology. Blocked Tear Duct. https://www.aao.org/eye-health/diseases/blocked-tear-duct
- American Academy of Ophthalmology. LASIK: Laser Eye Surgery. https://www.aao.org/eye-health/treatments/lasik
- National Eye Institute (NIH). Dry Eye. https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/dry-eye
- NHS. Watering eyes. https://www.nhs.uk/conditions/watering-eyes/
- NHS. Dry eyes. https://www.nhs.uk/conditions/dry-eye-syndrome/
- EyeWiki (AAO). Dry Eye Syndrome. https://eyewiki.org/Dry_Eye_Syndrome (TBUT about 10 s, osmolarity, Schirmer use, treatments)
- EyeWiki (AAO). Dacryocystorhinostomy. https://eyewiki.org/Dacryocystorhinostomy (indications, external vs endoscopic, success rates, recovery)
- EyeWiki (AAO). Congenital Nasolacrimal Duct Obstruction. https://eyewiki.org/Congenital_Nasolacrimal_Duct_Obstruction (about 5% of newborns; about 90% resolve in year one; probing 70–97%; dye test)
- Assessment and management of proximal and incomplete symptomatic obstruction of the lacrimal drainage system. Middle East Afr J Ophthalmol 2012. https://pmc.ncbi.nlm.nih.gov/articles/PMC3277026/ (puncta and canaliculi dimensions, sac size, success rates of procedures)
- Efficacy of mitomycin C in endoscopic dacryocystorhinostomy: systematic review and meta-analysis. PLoS One 2013. https://pmc.ncbi.nlm.nih.gov/articles/PMC3652813/ (endoscopic DCR success 84–94%)
- Diagnostic imaging of the nasolacrimal drainage system. Part I. Med Sci Monit 2014. https://pmc.ncbi.nlm.nih.gov/articles/PMC3999077/ (80–90% via lower canaliculus; 10–20% evaporation; lacrimal pump; congenital blockage 6–20%)
- Review: The Lacrimal Gland and Its Role in Dry Eye. J Ophthalmol 2016. https://pmc.ncbi.nlm.nih.gov/articles/PMC4793137/ (gland size, accessory glands, innervation, secretions)
- Tear film osmolarity and dry eye disease: a review of the literature. Clin Ophthalmol 2015. https://pmc.ncbi.nlm.nih.gov/articles/PMC4636089/ (302 ± 8 mOsm/L; 308 threshold)
- TFOS DEWS II pain and sensation report. Ocul Surf 2017. https://pmc.ncbi.nlm.nih.gov/articles/PMC5706540/ (corneal nerves, lacrimal functional unit, dry eye after refractive surgery)
- Dry eye disease: identification and therapeutic strategies for primary care clinicians. Ann Med 2023. https://pmc.ncbi.nlm.nih.gov/articles/PMC9809411/ (prevalence 5–50%; treatment ladder)
- Incidence and pattern of dry eye after cataract surgery. PLoS One 2013. https://pmc.ncbi.nlm.nih.gov/articles/PMC3827040/ (9.8% symptomatic at 7 days)
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