What are tears?
Tears are made up of three layers, known as the tear film:
- LIPID LAYER (OIL)
This layer of oil limits tear evaporation, lubricates the eye, makes it easier to blink, holds the tears in place and improves vision. It is produced by the meibomian glands, which are found in the upper and lower eyelids.
- AQUEOUS LAYER (WATER)
The aqueous layer is made up of 98% water, plus nutrients and proteins. This layer accounts for 90% of the tear volume. It hydrates (provides water to) and nourishes the cornea. It is protected by the lipid layer, which stops it evaporating. It is produced by the lacrimal gland, which is located in the upper eyelid.
- MUCIN LAYER (ADHESIVE)
The mucin layer is made up of mucins, which form a gel. Mucins are hydrophilic and ensure the tear is fixed firmly to the cornea and the conjunctiva. This layer also ensures that the aqueous layer is evenly spread across the surface of the cornea. It is produced by the mucus cells in the conjunctiva.
How do tears work?
Tears are secreted by the glands located inside the eyelids and the conjunctiva.
Tears are normally secreted at a rate of around 1 to 2 ml per minute.
Tears are secreted in two ways:
- Basal secretion occurs when you blink: the pressure of the blink stimulates the glands located inside the eyelids and the conjunctiva.
- Reflex secretion occurs due to psychological factors (e.g. emotions) or the presence of irritants (e.g. dust).
Tears are spread out by the eyelids when you blink, forming the tear film. A normal blinking frequency is once every 3 to 6 seconds.
Tears are then eliminated in two ways:
- Through evaporation (accounting for 70% of tear elimination):
- When blinking is less frequent
- When the tear film is exposed to the air
- Limited by the lipid layer
- Through the tear drainage system (accounting for 30% of tear elimination):
- Via the tear ducts
- As a result of blinking
What are tears for?
Tears are essential to the cornea. They play three key roles:
- Cleaning the eye surface
- Providing lubrication, so the eyelids can move more easily
- Hydrating and protecting the cornea (water, antibodies, complement system)
- Providing oxygenation and nutrients
- Optical support:
- Smoothing the surface of the cornea
- Maintaining its refractive properties, for optimal vision
What are the eyelids for?
The eyelids have two main functions:
- Protection: to prevent injuries to the surface of the eye
- Tear film maintenance: to secrete, distribute and drain away tears
Blinking has several essential functions:
- Ensures even distribution of the tears across the cornea
- Protects against foreign bodies and removes irritants
A normal blinking frequency is 10 to 20 times per minute, equivalent to once every 3 to 6 seconds.
What is dry eye?
Dry eye is one of the most common reasons for visiting an ophthalmologist, after sight testing. This very common disease affects the surface of the eye and the eyelids. There are several different forms of dry eye:
- Evaporative dry eye, also known as dry eye caused by meibomian gland dysfunction (MGD): the lipid layer is insufficient to limit tear (water) evaporation
- Aqueous-deficient dry eye: insufficient production of tears (aqueous layer)
- Mixed dry eye: evaporative and aqueous-deficient dry eye
The most common form is evaporative dry eye caused by meibomian gland dysfunction (over 80% of cases).
What do these different types of dry eye involve?
Dry eye can involve:
- Abnormal tear evaporation, due to insufficient lipids (oil)
- Poor tear production, due to insufficient water in the tears
- Unbalanced tear composition
- Low frequency, incomplete blinking
- Inflammation of the eyelids
What is evaporative dry eye caused by meibomian gland dysfunction (MGD)?
The meibomian glands are small glands located in the upper and lower eyelids that secrete the lipid layer of the tears. MGD causes the most common form of dry eye and results in:
- Reduced lipid (oil) production
- Poor quality oil: the oil hardens and blocks the meibomian glands, meaning it cannot be released
- Obstruction and atrophy of the meibomian glands
- Thinning of the lipid layer, which leads to excessive evaporation of the aqueous (water) layer
Does dry eye affect everyone?
Dry eye is most commonly linked to ageing. However, in recent years, there has been a marked increase in the number of cases of dry eye, due to a deterioration in our living conditions (pollution, air conditioning, heavy screen use etc.).
Today, almost one third of the adult population is affected. The same figure applies to children.
In February 2020, Galliléo carried out market research in France in partnership with Quantel Medical involving 400 patients with dry eye. The research found that dry eye affects people in every age bracket. The respondents were distributed as follows:
- Sex: 50% women, 50% men
- Age: 47% aged 18 to 44 years, and 53% aged 45 to 75 years
- 18–34 years: 31%
- 35–44 years: 16%
- 45–54 years: 21%
- 55–75 years: 32%
What are the causes of dry eye?
Dry eye can affect anyone and has a wide range of causes:
- AGE: As we get older, the lacrimal glands atrophy and cannot produce enough tears, or provide tears of poor quality.
- HORMONE IMBALANCES: Women are more likely to suffer from dry eye during pregnancy or after menopause.
- HEAVY SCREEN USE: This leads to less and incomplete blinking. We blink half as much when looking at a screen.
- MEDICATION: Certain medicines can cause dry eye, including antidepressants, painkillers, sleeping tablets, antihistamines, acne medication, diarrhoea medication, hormone therapy and eye drops containing preservatives.
- EYE SURGERY: Cataract and refractive (laser eye) surgery can damage the surface of the eye and cause or worsen dry eye.
- ENVIRONMENTAL CONDITIONS: Smoke, pollution, air conditioning, dry air, sun exposure etc. can all worsen dry eye.
- CONTACT LENSES: Long-term contact lens use can lead to dry eye.
- DEMODEX INFECTIONS: Demodex infections (eyelash parasites) can cause dry eye.
- INFLAMMATION: Diseases that cause inflammation of the eyelids (blepharitis), such as rosacea, seborrhoeic dermatitis, psoriasis, eczema and eye allergies can lead to dry eye.
- AUTOIMMUNE DISEASES: Sjögren’s syndrome, rheumatoid arthritis, HIV, hepatitis and other autoimmune diseases can all cause dry eye.
EXCESSIVE USE OF MAKE-UP ON THE EYELASHES: Using a lot of make-up on the eyelashes and along the edges of the eyelids increases the likelihood of dry eye.
What are the symptoms of dry eye?
The symptoms linked to dry eye can take several forms:
- Dry feeling, stinging, itching, irritation, burning, gritty feeling
- Tired eyes, blurred vision
- Sensitivity to light, wind or cigarette smoke
- Difficulty opening eyes in the morning (eyelids stuck together)
- No tears when cutting onions or feeling emotional
- Excessive tears when the weather is cold or windy, or when reading
- Difficulties wearing contact lenses
- Eyelid conditions (chalazion, styes, blepharitis, MGD, Demodex infection etc.)
Dry eye can often have a significant impact on everyday life: it can reduce how much time you are able to spend reading or at a computer, and can cause difficulty driving and pain.
How is dry eye diagnosed?
- Conventional tests:
Dry eye is caused by multiple factors and it may be diagnosed on the basis of several different examinations, including the following conventional tests:
- Questionnaire: There are several different questionnaires available to assess the severity of dry eye and its impact on the patient’s quality of life, including the DEQ-5 (Dry Eye Questionnaire), the OSDI (Ocular Surface Disease Index) and SPEED (Standard Patient Evaluation of Eye Dryness).
- Clinical analysis: It is important to check the appearance of the skin (for rosacea, eczema, psoriasis, seborrhoeic dermatitis), the anatomy of the eyelids, the appearance of the eyelashes and the patient’s blinking frequency, among others.
- Schirmer’s test: This test assesses the quantity of tears in the eye using a strip of filter paper placed within the lower eyelid. It is an invasive method, conducted without local anaesthetic. The filter paper gradually soaks up the tears. If the eye is not producing enough tears, the strip will have less than 10 mm of wetness after 5 minutes. The test is a means of quantitative analysis and is primarily used to measure aqueous-deficient dry eye, as in Sjögren’s syndrome.
- BUT (Break-Up Time): This test assesses the quality and stability of the tear film over the cornea. A drop of fluorescein is instilled into the patient’s eye. The patient must then keep their eyes open, without blinking, so that the time taken for the tear film to break up (visible with the fluorescein) can be measured. The test is positive if the tear film breaks before 10 seconds have elapsed. The test indicates that there is a problem with the lipid layer, causing excessive tear evaporation.
- New non-contact examinations:
Today, an increasing number of imaging devices are available to help better diagnose patients and enable more targeted treatment. New non-contact examinations are now available to assess tear quality and quantity, along with meibomian gland imaging.
The LacryDiag ocular surface analyser can carry out the following examinations:
- NIBUT (Non Invasive Break Up Time): This assesses the stability of the tears on the cornea. It measures how long a tear stays on the cornea after blinking and the point at which it breaks. A stable tear should have a NIBUT of more than 10 seconds.
- Interferometry: An examination used to assess the thickness of the lipid layer. The quality and thickness of the lipid layer are assessed based on its colour and structure (coloured fringes resembling a patch of oil). This test is very useful for diagnosing meibomian gland dysfunction.
- Measurement of tear meniscus height: This examination assesses the amount of water in the tears by measuring the height of the tear meniscus (the tear along the edge of the eyelid). If there is no tear meniscus, this indicates dry eye. The normal tear meniscus height is over 0.21 mm.
- Meibography: An examination that quickly produces a complete image of the shape of the meibomian glands. Meibography is used to assess meibomian gland loss, obstruction and atrophy.
- Blinking analysis*: This is used to count how many times the patient blinks and to identify any incomplete blinks. Incomplete blinking can often lead to meibomian gland dysfunction (MGD) and evaporative dry eye resulting from a poor lipid (oil) layer.
Is diagnosis long and painful?
Dry eye is caused by multiple factors and it may be diagnosed on the basis of several different examinations. Certain examinations may take longer than others. However, as a general rule, each test takes less than 5 minutes.
New, painless imaging tests are now being added to the existing options for diagnosing dry eye. These tests do not cause any pain, since most of them do not involve contact with the eye surface and are therefore non-invasive.
Schirmer’s test and BUT examination with fluorescein drops are both invasive examinations, since they require either filter paper to be placed on the conjunctiva or fluorescein to be dropped into the eye.
What types of treatment are available for dry eye?
Since dry eye is caused by multiple factors, its treatment is complex and can include a combination of several things:
- Cleaning, heating and massaging the eyelids
- Blinking exercises
- Tear substitutes
- Anti-inflammatory treatments
- Punctal plugs
- Scleral lenses
- Punctal occlusion
- Meibomian gland expression
- Intense pulsed light (IPL)
- And more…
Why use an IPL system to treat dry eye?
The LacryStim IPL (intense pulsed light) system is a dry eye treatment that works in several different ways:
- It stimulates and reactivates the meibomian and lacrimal glands: tear production is stimulated by the nervous system, via the parasympathetic nerve, which is linked to the lacrimal gland and meibomian glands.
- Intense pulsed light stimulates the parasympathetic nerve located under the lower eyelid, reactivating the gland metabolism.
- It reduces inflammatory lesions (rosacea and blepharitis): when the skin is affected by rosacea, abnormal blood vessels cause vasodilation, which releases inflammatory agents (cytokines) in the tears. The inflammation extends to the eyelids, causing inflammation of the eyelids (blepharitis) and blocking the meibomian glands.
- Intense pulsed light coagulates the small blood vessels in the skin (rosacea), indirectly improving eyelid inflammation (blepharitis).
LacryStim is a high-tech intense pulsed light (IPL) system that provides safe, painless, effective and long-lasting treatment for most skin types.
What happens during LacryStim IPL treatment?
IPL treatment with LacryStim involves the following:
- Three sessions spaced out by 7 to 15 days
- A fourth session may be recommended
- One follow-up session after several months may be recommended
- Sessions are quick (less than 10 minutes), painless and do not require anaesthesia
A LacryStim session involves the following:
- Before your appointment, you will need to clean your skin, applying no creams or make-up, and shave if you are a man
- A thin layer of transparent gel is applied to the treatment area
- You then put on protective goggles provided by your doctor
- Four shots are applied to the cheek. You may feel gentle heat and some tingling
- You then remove your protective goggles. Your skin will be cleaned and a moisturising cream may be applied
Are there any new treatments for dry eye?
New, painless treatments are now being added to the existing options for treating dry eye. Intense pulsed light (IPL) is one of the new innovative technologies for the treatment of dry eye recognised in the TFOS-DEWS II international scientific report.
Is IPL treatment painful?
IPL treatment is painless and does not require anaesthesia. When the flashes of light are applied to the skin, you may feel a tingling sensation and heat.
What results can I expect from IPL treatment?
- Improved tear quality
- A reduction in symptoms
- Reduced inflammation of the face and eyelids, and fewer Demodex (eyelash parasites)
- A lasting improvement (several months)
What kinds of patients are eligible for IPL treatment?
IPL treatment is suitable for patients who:
- Have meibomian gland dysfunction (MGD) or lacrimal gland dysfunction
- Have inflammatory lesions (rosacea and/or blepharitis)
- Find it difficult to keep up with treatments
- Have tried other treatments without success
- Struggle to keep up with massage therapy
Talk to your ophthalmologist to find out whether you are eligible for treatment.
Are there any treatments that offer long-term results?
The effects of each treatment can last for a varying length of time, based on several factors:
- The type of treatment prescribed: not all treatments are as effective as each other, but combining treatments can result in long-term effects
- How well the patient complies with the prescribed treatment: if the patient does not follow the treatment, it will be less effective
- The type of dry eye and its severity
- Dry eye can sometimes be caused by another condition. If this is the case, the source of the problem will need to be treated and a specialist consulted. Possible causes include auto-immune diseases (e.g. Sjögren’s syndrome, rheumatoid arthritis, hepatitis), medication (e.g. oral acne drugs, oral contraceptives, diuretics, neuroleptics, eye drops containing preservatives) and inflammatory skin lesions (e.g. rosacea, blepharitis, seborrhoeic dermatitis, psoriasis).
- Treatments can be made more effective by combining them with daily eyelid care and simple actions that you can take yourself (see FAQ “What actions can I take myself if I have dry eye or want to prevent it?”).
Everyone is different and the condition varies from one person to another. Visit an ophthalmologist to identify what type of dry eye you have and which treatments are suitable.
Good to know
Why is blinking important?
The eyelids and the act of blinking both play essential roles:
- Blinking the eyelids protects the eyes from injury and enables tears to be secreted, spread out and drained away.
- The act of blinking stimulates the glands in your upper and lower eyelids that produce the oil in your tears, ensures that your tears are spread evenly across the cornea and protects the eyes from foreign bodies.
- A normal blinking frequency is around 15 times per minute, equivalent to once every 4 seconds.
What actions should I take when I spend a long time in front of a screen?
Here are a few simple actions you can take when you are working at a computer screen or using your phone or tablet:
- Take breaks of at least 5 minutes every hour when working at a screen, and look into the distance regularly
- Remember to blink every 4 to 6 seconds when using a screen, as we often blink two times less than normal
- Do not work at a screen in the dark or with too much light: ensure there is enough light and that it is consistent across the room. Natural light is best. Always place a small light behind the screen
- Position your computer screen lower than your eyes, so you are not looking upwards, which exposes your eyes to more air
- Use a screen filter on your computer to reduce the impact of blue light
- Limit your screen time