Dry eye syndrome (DES) is a common disorder of the tear film, affecting a significant percentage of the population; especially those older than 40 years of age. DES can affect any race and is more common in women than in men.
Role of Tear Film in Eye
To help keep your eyes comfortable and your vision optimal, a normal, thin film of tears coats your eyes. Three main layers make up this tear film
The innermost layer is the thinnest. It is a layer of mucin (or mucus). This very thin layer of mucus is produced by the cells in the conjunctiva (the clear skin that lines the eye). The mucus helps the overlying watery layer to spread evenly over the eye.
The middle (or aqueous) layer is the largest and the thickest. This layer is essentially a very dilute saltwater solution. The lacrimal glands under the upper lids and the accessory tear glands produce this watery layer. This layers function is to keep the eye moist and comfortable, as well as to help flush out any dust, debris, or foreign objects that may get into the eye. Defects of the aqueous layer are the most common cause of dry eye syndrome.
The most superficial layer is a very thin layer of lipids (fats or oils). These lipids are produced by the meibomian glands and the glands of Zeis (oil glands in the eyelids). The main function of this lipid layer is to help decrease evaporation of the watery layer beneath it.
Dry Eye Syndrome Causes
DES is a common disorder of the normal tear film that results from one of the following:
- Decreased tear production
- Excessive tear evaporation
- An abnormality in the production of mucus or lipids normally found in the tear layer
Aqueous (watery) tear deficiency is caused by either poor production of watery tears or excessive evaporation of the watery tear layer.
Poor production of tears by the tear glands may be a result of age, hormonal changes, or various autoimmune diseases, such as primary Sjogren syndrome, rheumatoid arthritis, or lupus.
Evaporative loss of the watery tear layer is usually a result of an insufficient overlying lipid layer.
Some Other Causes
Some medications, such as antihistamines, antidepressants, beta-blockers, and oral contraceptives, may decrease tear production.
If blinking is decreased or if the eyelids cannot be closed, the eyes may dry out because of tear evaporation.
When you read, watch TV, or perform a task that requires close attention with your eyes, you may not blink as often. This decreased blinking allows excessive evaporation of the tears.
Certain conditions, such as stroke or Bells palsy, make it difficult to close your eyes on your own. As a result, your eyes may become dry from tear evaporation.
Abnormal production of mucin by the conjunctiva may occur.
This can result from chemical (alkali) burns to the eye or as a result of different autoimmune diseases, such as Stevens-Johnson syndrome and cicatricial pemphigoid.
This abnormal production of mucin leads to poor spreading of the tears over the surface of the eye. The surface of the eye can dry out and even become damaged, even though more than enough watery tears may be present.
Insufficient lipid layers are the result of meibomian gland dysfunction, as with rosacea or as a result of taking oral isotretinoin medication.
Meibomian glands are the oil glands in the eyelids that produce the lipid layer.
If the oil glands become blocked or if the oil is too thick, there may not be enough oil to cover the watery tear layer to prevent its evaporation.
Also, if an infection is present along the eyelids or the eyelashes, called blepharitis, the bacteria may breakdown the oil so there may not be enough oil.
Dry Eye Syndrome Symptoms
- Dry, gritty/scratchy, or filmy feeling in the eyes
- Burning or itching in the eyes
- Redness of the eyes
- Blurred vision
- A sensation of having a foreign body in the eyes
- Light sensitivity
- Contact lens intolerance can also be a symptom of dry eye. Often, a person with mild to moderate dry eye may not experience symptoms until contact lenses are fitted. The placement of a contact lens can upset the delicate balance of tear film production and distribution, leading to lens intolerance.
Avoidance of Dry Eye Syndrome
As obvious as it may sound, blink more often. Take breaks between activities that require intense eye focus such as reading or working on the computer. Other tips to prevent the onset or progression of dry eye include:
Monitor the humidity indoors. Consider adding a humidifier if the air feels dry.
Avoid heavily polluted areas whenever possible.
Drink 8 to10 glasses of water a day to stay hydrated.
Dont smoke. Smoking increases the likelihood that you will suffer from dry eye symptoms.
Dry Eye Treatment
Artificial tears and lubricating eyedrops and gels (available over the counter) help provide more moisture and lubrication for the surface of your eye. They are typically used about four times a day, but they can be used as often as needed. Preservative-free solutions are recommended if you wish to use artificial tears more than six times a day. There is no single over-the-counter drop that is best for everyone. Each individual will determine which drop provides the most relief from symptoms. Some drops may have a longer effect than others.
Lubricating eye ointments are much thicker than eyedrops and gels. Because ointments are so thick, they last much longer than eyedrops and gels. However, because of their thickness, ointments may blur your vision if used during the day. Therefore, they are typically used to lubricate the eyes overnight while you are asleep.
