Overview

Dry eye syndrome (also called keratoconjunctivitis sicca) is a condition that occurs when there is not enough aqueous (the watery part of tears). You might also have symptoms of dry eye syndrome if there is not enough of other parts of the tears, such as mucus and lipid. This can happen if you have an eyelid or conjunctival disease, such as inflammation of the eyelids (blepharitis), or when normal blinking is disrupted by neurological or eyelid problems. 

About your tears

We tend to notice tears when something is very funny, or very sad. If your eyes are healthy, glands in your eyes are making tiny amounts of the same liquid all of the time. This is known as the ‘tear layer'. This layer helps to protect your eye, and allows you to see clearly.

The tear layer is made up of 3 main components. 

Aqueous (water) 

Tears are mostly made of water. This is produced by the lacrimal gland, which is above your eye, underneath your eyelid. Water is needed to moisten the eye, wash away debris and provide a smooth corneal surface to help your eye focus. The lacrimal gland also makes antibodies and antibacterial elements to protect your eye.

An oily outer layer

This layer is produced mainly by the glands (Meibomian glands) in your eyelids. This layer lubricates your eye, which helps you blink. The oil also stops your tears from evaporating too quickly. 

An inner mucus layer

This layer is produced by glands within the conjunctiva. The conjunctiva is the clear layer that covers the white part of your eye and the inside of your eyelids. The mucus layer helps to spread tears over the surface of your eye. 

Causes of dry eye syndrome

Aging

Dry eyes occur naturally as you age, especially after the menopause.

Medicines

These are some of the medicines that can reduce your lacrimal gland secretions:

• some varieties of antihistamines and decongestants
• certain antidepressants
• some blood pressure medicines (including diuretics)
• medicines for Parkinson’s disease
• contraceptive pills
• opiate-based pain relief (such as morphine)
• isotretinoin-type medicine

Laser eye surgery (LASIK)

Some people who have had certain types of laser eye surgery find they have dry eyes in the weeks after surgery. This is usually a result of damage to the corneal nerves. The nerves usually regenerate and dryness typically improves. Sometimes, it can cause permanent problems, and people who already have significant dry eye syndrome should not have LASIK treatment.

Other medical conditions

Some medical conditions can cause inflammation or destruction of the lacrimal gland, leading to impaired aqueous production.

These include:

• Sjögren's syndrome, which can occur on its own or with other rheumatological diseases, such as rheumatoid arthritis or systemic lupus erythematosis
• ocular cicatricial pemphigoid or Stevens-Johnson syndrome. These can cause conjunctival scarring, which causes dry eyes by blocking the lacrimal gland ducts. Conjunctival scarring can also happen as a result of chemical burns
• blepharitis (causes inflammation of the eyelids) and similar conditions which might cause meibomian gland dysfunction. This damages the production of the other components of tears (lipid and mucous), making the eyes dry.
• neurological problems, including stroke and Bell’s palsy, which can affect your ability to blink or close your eyelids. This prevents the spread of tears over the eye and allows your tears to evaporate causing dry eyes.

Symptoms of dry eye syndrome

There are several symptoms of dry eye syndrome. You might have all, or just some of them. Symptoms include:

• itchy eyes or a gritty feeling in your eye
• a burning sensation in your eye
• stringy mucus in your eye
• blurred vision
• sensitivity to light
• red eyes
• lack of tears when you cry

Your symptoms can be made worse by:

• windy weather
• dusty and smoky environments
• central heating and air conditioning

You can improve your symptoms by closing your eyes.    

Diagnosing dry eye syndrome

Dry eye syndrome is diagnosed using a slit lamp. A slit lamp is a special microscope that eye doctors (ophthalmologists) use to give a magnified image of your eye. A slit lamp allows us to see if:

• the tear meniscus on the lower lid margin is smaller
• there are strands of mucus in the tear film
• there are abnormalities on the cornea, or loss and damage to the corneal skin cells (epithelium skin cells)

The damaged areas can be highlighted using a yellow dye called fluorescein. You might also have some tests to help us with our diagnosis. These include:

Tear break-up test 

This test helps us to see if you have a healthy tear layer. The doctor will put droplets of yellow dye into your eye, which makes the tear layer visible. Your doctor will then time how long it takes for the tear layer to break-up and dry out. If this takes less than 10 seconds, your eyes are drying out too quickly. 

Schirmer test

Your doctor will place 1 end of a thin strip of filter paper inside your lower eyelid. The other end will stick out. They will measure the amount of liquid the paper soaks up in 5 minutes. This test can also be done using special cotton threads.

Tear samples

Your doctor can examine your tears by taking a sample. This can help if they want to check your enzyme levels. 

Special dye test

Your doctor might use a special dye to check for damaged cells on the surface of your eye.