Dry eye syndrome: Understanding the causes of dry eyes
Dry eye syndrome is caused by a chronic lack of sufficient lubrication and moisture on the surface of the eye.
Consequences of dry eyes range from subtle but constant eye irritation to significant inflammation and even scarring of the front surface of the eye.
In addition to being called dry eye syndrome, dry eye disease, or simply "dry eye," alternative medical terms used to describe dry eyes include:
Keratitis sicca Generally used to describe dryness and inflammation of the cornea.
Keratoconjunctivitis sicca Used to describe dry eye that affects both the cornea and the conjunctiva.
Dysfunctional tear syndrome
Used to emphasise that inadequate quality of tears can be just as important as inadequate quantity.
Prevalence of dry eye
Dry eye syndrome — also called dry eye disease (DED) — is one of the most common eye conditions worldwide and a primary reason for visits to the optician.
In a review published in the Journal of Global Health, researchers reported that studies have shown the prevalence of dry eyes ranges from 5 percent to as high as 50 percent in different populations across the world. (The researchers felt the large variation may be due to disparities in diagnostic criteria of different studies, unique characteristics of the investigated populations and other factors.)
Risk factors for dry eye syndrome included advanced age, female sex, and computer use.
Dry eye symptoms
Symptoms of dry eyes and dry eye syndrome include:
Another common symptom is something called a foreign body sensation — the feeling that grit or some other object or material is "in" your eye.
This is because dryness on the eye's surface sometimes will over-stimulate production of the watery component of your tears as a protective mechanism. But this "reflex tearing" does not stay on the eye long enough to correct the underlying dry eye condition.
In addition to these symptoms, dry eyes can cause inflammation and (sometimes permanent) damage to the surface of the eye.
What causes dry eye syndrome?
An adequate and consistent layer of tears on the surface of the eye is essential to keep your eyes healthy, comfortable and seeing well.
Tears bathe the eye's surface to keep it moist and wash away dust, debris and microorganisms that could damage the cornea and lead to an eye infection.
A normal tear film consists of three important components:
An oily (lipid) component
A watery (aqueous) component
A mucous-like (mucin) component
Each component of the tear film serves a critical purpose. For example, tear lipids help keep the tear film from evaporating too quickly and increase lubrication, while mucin helps anchor and spread the tears across the surface of the eye.
Each tear component is produced by different glands on or near the eye:
The oily component is produced by meibomian glands in the eyelids.
The watery component is produced by lacrimal glands located behind the outer aspect of the upper eyelids.
The mucin component is produced by goblet cells in the conjunctiva that covers the white of the eye (sclera).
A problem with any of these sources of tear film components can result in tear instability and dry eyes.
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Dry eye categories
There are different categories of dry eyes, depending on which component is affected.
For example, if the meibomian glands don't produce or secrete enough oil (meibum), the tear film may evaporate too quickly — a condition called "evaporative dry eye."
The underlying condition — called meibomian gland dysfunction — is now recognized as a significant factor in many cases of dry eye syndrome.
In other cases, the primary cause of dry eye is a failure of the lacrimal glands to produce enough watery fluid (aqueous) to keep the eyes adequately moistened. This condition is called "aqueous deficiency dry eye."
The specific type of dry eye often will determine the type of treatment your optician recommends to give you relief from your dry eye symptoms.
Factors associated with dry eye syndrome
A number of factors can increase your risk of dry eyes. These include:
When working at a computer or using a smartphone or other portable digital device, we tend to blink our eyes less fully and less frequently, which leads to greater tear evaporation and increased risk of dry eye symptoms.
Contact lens wear
Though it can be difficult to determine the exact extent that contact lens wear contributes to dry eye problems, dry eye discomfort is a primary reason why people discontinue contact lens wear.
Dry eye syndrome can occur at any age, but it becomes increasingly more common later in life, especially after age 50.
Post-menopausal women are at greater risk of dry eyes than men of the same age.
Air conditioning, ceiling fans and forced air heating systems all can decrease indoor humidity and/or hasten tear evaporation, causing dry eye symptoms.
Arid climates and dry or windy conditions increase dry eye risks.
The air in the cabins of airplanes is extremely dry and can lead to dry eye problems, especially among frequent flyers.
Certain systemic diseases — such as diabetes, thyroid-associated diseases, lupus, rheumatoid arthritis and Sjogren's syndrome — contribute to dry eye problems.
Many prescription and nonprescription medicines — including antihistamines, antidepressants, certain blood pressure medications and birth control pills — increase the risk of dry eye symptoms.
Incomplete closure of the eyelids when blinking or sleeping — a condition called lagophthalmos, which can be caused by ageing or occur after cosmetic blepharoplasty or other causes — can cause severe dry eyes that can lead to a corneal ulcer if left untreated.
Also, LASIK and other corneal refractive surgery can sometimes cause dry eyes. In most cases, however, dry eye discomfort after LASIK is temporary and resolves within a few weeks of the procedure.
If you have dry eyes prior to LASIK, your optician may recommend a dry eye treatment programme before your procedure to insure the best possible LASIK results.
Dry Eye News
Smartphone use linked to dry eye in schoolchildren
There might be another cost associated with children using smartphones besides a large monthly bill from the phone company — it could be causing kids to develop dry eye disease at an early age.
Researchers in Korea evaluated risk factors for dry eye disease among schoolchildren who used video devices, including smartphones.
The researchers examined 916 schoolchildren from grades 1 through 6 for signs of dry eye disease. They also had the children and their parents complete a questionnaire concerning the types of video devices the children commonly used (computer, smartphone and television) and the amount of time they spent using each device. Data regarding the amount of time the children spent outdoors also was gathered.
Overall, a total of 6.6 percent of the children were found to have signs of dry eye disease. Children living in an urban setting were more likely than children in rural settings to have DED (8.3 percent vs. 2.8 percent). The rate of smartphone use was 61.3 percent in the urban group and 51.0 percent in the rural group.
When evaluated by age, 9.1 percent of children aged 9 to 12 were diagnosed with DED, compared with 4.0 percent of children aged 6 to 9. The rate of smartphone use was 65.1 % in older children and 50.9 % in younger children.
Also, the amount of time children spent using smartphones was longer in the DED group, compared with children without dry eye. After the children with dry eyes stopped using their smartphones for 4 weeks, both their subjective symptoms and objective signs of dry eye improved.
The study authors concluded that smartphone use in children was strongly associated with paediatric dry eye disease. Older students in urban environments had the greatest risk factors and prevalence of DED.
The authors also pointed out that signs and symptoms of dry eyes improved when smartphone use was discontinued, and that increased outdoor activities appeared to be protective against paediatric dry eye disease.
Dry eye tests
The only way to know for sure if you've got chronic dry eye syndrome is to have your optician perform one or more dry eye tests during an eye exam.
Symptoms alone are poor predictors of the presence and severity of dry eye disease. Symptoms can vary significantly from person to person, and may even be affected by personality type.
Some people with only minimal or mild dry eyes may feel their eyes are very bothersome, while others may have significant dry eye problems and not consider their symptoms significant enough to see an optician (or they may not experience dry eye symptoms at all).
Only a careful examination of your eyes by by an optician can reveal the presence and severity of dry eye syndrome and help your optician determine the best type of dry eye treatment to keep your eyes healthy, comfortable and seeing well.
Dry eye treatment and prevention
In many cases, routine use of artificial tears and minor behavioral modifications (taking frequent breaks during computer use, for example) can significantly reduce dry eye symptoms.
In other cases, your optician might recommend prescription eye medications and in-office procedures to help your body create and secrete more tears and to decrease eye irritation and inflammation.