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Dry Eye Syndrome
Dry eye syndrome (also known as keratoconjunctivitis sicca or KCS) is one of the
most common ocular conditions. It is characterized by decreased production of
natural tears. Most cases are mild, but it often can affect your comfort and ocular
health. Despite greater understanding of tear film production, the underlying
cause of dry eyes is usually unknown. However, various treatments are available
to afford some relief from their chronic ocular problem.
The Normal Tear Film
The tears form a moist layer over the surface of the eye, including the cornea
and conjunctiva. Since the tear layer is the outermost surface of the eye, it acts
as an interface between the eye and the outside environment. There are several
important functions of the tear film. It moistens and protects the surface cells
(epithelium). Without that moisture the cells can harden and look more like the
skin over the rest of your body. The tear film also provides a smooth, transparent
surface that helps focus light entering the eye, and is necessary for sharp, clear
vision. Our tears also serve as a vehicle for oxygenation and nourishment of the
ocular surface. Finally, the tear film contains several substances that help protect
the ocular surface against infection.
The film is comprised of three layers, each essential to maintaining the health of
the eye (FIG. 1). Abnormalities of any of these layers can cause a tear
dysfunction problem. The inner most layer is made of mucin produced by cells in
the conjunctiva, and helps the tears spread smoothly over the ocular surface
(wettability). The thick middle layer is composed primarily of water, and is
produced by the lacrimal gland. Finally, the outer lipid layer, produced by the
meibomian glands, enhances the stability of the middle aqueous layer by
retarding tear film evaporation.
A deficiency in any one of these layers can result in the symptoms of dry eye.
Although the dry eye syndrome most commonly results from an insufficient
aqueous layer. It may also result from an abnormal lipid or mucins layer or from
problems in eyelid function and blinking.
Normally tears are produced constantly by the lacrimal glands. Tear production
increases in response to dryness, irritation, or emotions. The tears flow over the
ocular surface, being spread and smoothed by the blinking of the lids, and
eventually drain away from the eye through the lacrimal ducts at the inner corner
of each lid, into the nose.
What are the symptoms of dry eyes?
The most common symptoms are:
Dryness
Burning
Irritation
Sandy, gritty feeling
Redness
Blurred vision
These symptoms usually affect both eyes, but only one can be affected. The
eyes typically get worse as the day progressed, and can become more
pronounced when reading or watching TV. Some patients may be especially
sensitive to dry or irritating environments, such as dry heat, warm or smoke-filled
rooms, and wind. Sensitivity to light may also be reported.
How is dry eye diagnosed?
The signs of dry eye are often subtle, and the eye doctor may not make the
diagnosis unless he or she specifically tests for it. The following are often used
and can be very helpful in detecting dry eyes.
Vital Dye Stains
Rose bengal (rose colored) and lissamine green dyes adhere to the ocular
surface where it is dry or irritated. The amunt and pattern of staining can
tell the doctor what is causing your symptoms
Tests of Tear Production
Theses tests involve placing a small strip of paper or a thread under the
lower lid and measuring how much tears it absorbs over a small period of
time. These tests are simple and make the diagnosis if the result is low,
however, they often miss mild cases of dryness.
Tear Break-up Time (BUT)
The tear break-up time (BUT) is a direct measure of the stability of the
preocular tear film. A normal tear film with sufficient lipid, aqueous, and
mucinous layers begins to break up, or show signs of discontinuity, after
approximately 10 seconds. This process is generally accelerated in
patients with dry eyes.
What is the cause of dry eyes?
In most cases a cause is never found. The chance of having dry eyes is greater
in women and the older you get. It is associated with some medications, such as
antihistamines or diuretics. Dryness can also result from severe ocular infections
or injuries, such as chemical burns. In some cases dry eyes is associated with
dry mouth or a systemic disease.
What is Sjogren’s syndrome?
Sjogren’s syndrome is the combination of dry eyes and dry mouth or dry eyes
and a systemic autoimmune disease, such as rheumatoid arthritis or lupus
erythematosis. The combination of dry eyes and dry mouth alone is called
primary Sjogren’s syndrome, and can be associated with inflammation elsewhere
in the body. A thorough general physical examination and some blood tests are
necessary to make the diagnosis of primary Sjogren’s syndrome. In most cases
the only treatment is of the ocular and mouth dryness.
Treatment of dry eyes
At present, there is no cure for dry eyes; there is no way to restore your tear
production to normal. However, there are a number of ways to ameliorate the
symptoms. In general, patients suffering from dry eyes will benefit from a moist,
humid environment. A warm, dry room can be made more tolerable by using a
home humidifier and by avoiding smoke or dust. Swimmer's goggles or even side
shields with spectacles increase the humidity in the environment immediately
around the eye, and delay the evaporation of tears.
Artificial Tear Preparations
Artificial tears remain the primary treatment for mild to moderately dry eyes.
They are made to simulate the aqueous (liquid) layer
of your natural tears. Most artificial tears also have a
thickening agent to improve lubrication and help
them last longer by retarding evaporation. The most
common thickening agents are derivatives of
cellulose or polyvinyl alcohol. Unfortunately, placing
a drop of tears in your eye cannot replace the natural
constant flow of tears over the eye. Before long, the
artificial tear drops evaporate or drain from the eye (through the natural tear
drainage ducts that lead from the eye to the nose). Therefore, you may need to
instill the drops frequently (as often as every 15 minutes) to keep the eyes moist.
There are a large variety of commercially made artificial tear preparations. They
generally can be divided into three types:
Tear solutions with preservatives
The available tear solutions vary widely and change every year. No one
type is best for everyone. You have to try several and find the one that
provides you the most relief. All of these drops come in a small bottle and
contain preservatives so that the bottle does not become contaminated
while you are using it. Unfortunately the preservatives can cause irritation
and injury to the surface cells, particularly if the drops are used very
frequently or if the eyes are very dry. New, less-irritating, preservatives
are constantly being developed, so some products are safer to use than
others, but any can cause problems.
Tear solutions without preservatives
For this reason many preservative free preparations have been made
available. Since there is no preservative these products are packaged in
very small plastic dispensers that must be discarded the day they are
opened. Although much less convenient and more expensive than tears
in larger bottles, they are the best products for people requiring drops
every 2 hours or more or who are sensitive to a preservative.
Lubricating ointments and gels
These are more viscous so they lubricate better and stay in the eye
longer, however they often blur your vision. Therefore most people use
them at bedtime or when their symptoms are especially severe. In
general the gels are in-between drops and ointments.
RESTASIS
Restasis (cyclosporine ophthalmic emulsion 0.05%) is an exciting new treatment
for dry eyes. Unlike artificial tears, Restasis is the first drug proven to increase
tear production in some patients with dry eyes. Researchers have found that
inflammation in the surface cells contributes to dry eyes. Restasis quiets this
inflammation.
Restasis is most likely to benefit patients with moderate dry eyes (as opposed to
mild or severe). It is an eyedrop that is instilled twice daily in addition to your
usual artificial tears. If the restasis works your comfort will improve and most
likely your need for artificial tears will lessen.
The most common side effect of Restasis is a temporary burning sensation.
Many patients see an improvement in 1 month, however, you may not see the
effect of Restasis until you have been using it for 3 months, and it takes about 6
months to get the maximum effect. You have to keep using the drops to maintain
the effect. Keep in mind that Restasis is a treatment, not a cure.
Tear Conservation by Punctal Occlusion
Conserving existing tears by reversible (punctal plugs) or irreversible (punctal
cautery) punctal occlusion can be of tremendous benefit to dry eyes patients with
severe tear deficiency. Punctal occlusion prolongs the action of artificial as well
as natural tears by retaining them longer on the eye. One method of occlusion is
to place a silicone punctal plug into the tear drainage holes of the lids. The
advantage of this type of punctal occlusion is its reversibility. If punctal plugs
appear to relieve the symptoms of dry eyes with few or no problems, then
permanent punctal occlusion via cautery may be considered.
Partial or Total Tarsorrhaphy.
In severe cases of dry eye it is appropriate to consider partial or total surgical
closure of the eyelids. This is known as a tarsorrhaphy. This procedure
decreases the surface area that the eye needs to keep lubricated.
Dietary supplements
It appears that a high dietary intake of omega-3 essential fatty acids decreases
the risk of dry eye. A recent study found that thre was a relationship between
omega-3 fatty acids in the diet and the likelihood of dry eyes. Using the
Women’s Health Database at the Harvard School of Public Health, the
investigators examined the dietary intake of essential fatty acids in 32,470 female
health professionals. They found that the higher the dietary ratio of omega-3 to
omega-6 essential fatty acids, the lower the likelihood of dry eye, and the higher
the dietary omega-3 intake, the lower the likelihood of dry eye. Conversely, they
found that the lower the ratio of omega-3s to omega-6s the higher the likelihood
of dry eye.
Based on this finding, doctors have tried omega-3 supplements to treat dry
eye. In some patients the supplements appear to lessentheir symptoms.
Treatment is started at 2-4 capsules twice daily. If it is going to help you will
see a response in 4 to 8 weeks.
For more information explore the manufacturer’s web site:
http://www.dryeyeinfo.org/Dry_Eye_In_Depth.htm