What is Dry Eye Syndrome?
Dry eye syndrome (or keratoconjunctivitis sicca (KCS)) is the name given to the condition characterized by a lack of the required quantity or composition of tears to properly lubricate the eyes. It is a relatively common condition that increases in frequency with age. Dry eye syndrome affects roughly twice as many women as it does men. Approximately 9 million Americans suffer from the condition.
Tears are vital to the healthy functioning of the eye. They assist in keeping the eye comfortable and the vision optimal. The film of tears that do this job are composed of three layers. The innermost layer is made of mucus which is produced by and covers the clear skin that lines the eye (conjunctiva). The middle layer is composed of a diluted saltwater solution. This layer serves to keep the eye moist and comfortable, as well as flushing out foreign objects like dust. The outermost layer is composed of lipids (fats and oils) and primarily serves to protect the middle layer.
Dry eye syndrome is usually caused as a result of a defect in the middle or aqueous layer of the tear film which leads to either decreased tear production or increased tear evaporation.
Causes of Dry Eyes
There are two major causes of dry eye syndrome, each one connected to the quality and consistency of the tear film that lubricates the eye:
- Decreased tear production: The most common cause of dry eye syndrome is a decrease in the production of the aqueous tear layer. This is known as Aqueous tear deficiency (ATD) or lacrimal hyposecretion. The lacrimal gland is the gland responsible for tear production. As we age, the lacrimal gland lessens it’s production rate. In some cases, ATD may be a symptom of a collagen vascular disease such as rheumatoid arthritis or systemic lupus erythematosus. Certain medical drugs, including some sedatives, diuretics and oral contraceptives have been found to exacerbate and, in some cases, cause ATD. (Meadows, Michelle (May-June 2005). Dealing with Dry Eye. FDA Consumer Magazine. U.S. Food and Drug Administration).
- Excessive tear evaporation: Dry eye syndrome due to excessive tear evaporation is known medically as evaporative dry eyes. Tear production rate is not hampered. However, the rate of evaporation is abnormally accelerated. The tears lack water and, as a result, are too salty (hypertonic).
Additional causes of dry eye syndrome are eye injuries or abnormalities such as drooping eyelids or bulging eyes. The condition is also common to people who wear contact lenses. The contact lens can actually absorb the tears in the eye. Refractive surgery can also lead to dry eye syndrome during the surgery recovery period, but the condition should be alleviated over time.
Blepharitis is the medical name for inflammation of the eyelids. The condition is characterized by redness of the eyes and itchy eyelids. It is easily mistaken for dry eye syndrome. While it is different condition, blepharitis can be a contributory factor to dry eye syndrome.
As we age our bodies produce less oil. This lowering of production of oil has an impact upon the quality of the tear film. Because there is less oil to protect the watery layer, the film evaporates more quickly. This leaves dry areas on the cornea.
Environmental factors can also contribute to dry eye syndrome. Dry, windy climates contribute to excess tear evaporation as can cigarette smoke and air-conditioning.
Anatomy of Dry Eyes
Tears: Humans produce three types of tears – basal or continuous tears which moisten the eye; reflex tears which spring into action when the eye is irritated by some foreign object and emotional tears. Tears are formed in the glands that surround the eyes.
Continuous tears do much more than water your eyes. Let’s chart the course of this marvelous fluid as it is produced, spread, and expelled through the lacrimal system.
The main tear gland is found in the depression just above the outer corner of your eye. This spongy gland, along with 60 others, creates a precision film made up of three layers—mucus, aqueous, and oil.
The inner layer, the mucous, makes a smooth surface so the lid glides across the exposed eyeball. The aqueous layer is the thickest of the three, containing many important ingredients including oxygen, vital to the cornea. Also add a dose of lysozyme and 11 other enzymes found in tears. Lysozyme is a bacteria fighter par excellence. It keeps the eye white and clear.
The finishing touches on this tear will be supplied by 30 Meibomian glands, those little yellow dots lining both lids in single file behind the lashes. The glands secrete the oil layer, so thin that it doesn’t distort your vision, yet keeps the tear film from evaporating and causing uncomfortable dry spots on the eye between blinks. In fact, some people have an inadequate supply of oil, and their tears evaporate much faster than normal.
When the lid sweeps down over the eye it draws out just the right blend of ingredients, and spreads them evenly across the eye in three layers. The lids meet perfectly so that the entire surface of the exposed eye is bathed in this soothing wash.
What happens to the used tears? A close look at your eye will show a tiny hole in the inner corner, the punctum, that drains the excess tears into a channel leading to the tear sac. From there the tears pass down the back of the nose and throat, where the tears are absorbed by the mucous membranes. Blinking causes the tear sac to act like a pump, which propels the tears into the canal and downward.
Eye Anatomy: The eyeball, or “globe,” is round, except at the front, where it has a bulge. This bulge contains the light-gathering apparatus of the eye. The ‘skin’ of the entire eyeball is opaque [nontransparent] to light except at this bulge, where it is normally a beautifully clear and round window called the cornea.
Behind the cornea is the colored iris, with a hole, or pupil, at its center. The iris automatically increases or decreases the size of the pupil to control the amount of light entering the eye.
Just behind the iris is the crystalline lens. This works together with the cornea to focus light at the rear of the eyeball, where it is converted into electrical impulses that are transmitted to the visual center of the brain. It is the brain, not the eyes, that actually does the “seeing.”
Back of the lens the eyeball is filled with vitreous humor. This is a transparent jellylike substance made up mostly of water, with a tiny percentage of solids.
The “skin” of the eyeball consists of three layers. The outermost layer is the sclera. It is tough, fibrous and opaque over most of the eye, preventing light from entering. At the front, however, the sclera becomes the transparent cornea.
The middle layer of this skin is highly complicated. At the front of the eyeball it separates into other structures, including the iris. However, over four fifths of the eyeball it forms an essentially continuous layer called the choroid.
The third or innermost layer of the eyeball’s three-ply skin is the retina. The retina is a paper-thin membrane that gives the light-images entering the eye the shape, color and texture that the brain perceives. Though “paper thin,” the retina consists of many distinct layers. It, consists of three main layers of cells: (1) nerve cells toward the central cavity, (2) light-sensitive cells in the middle, and (3) pigment-containing cells toward the outside near the choroid.”
The light-sensitive cells in the retina number many millions. Each eye contains some 130 million rods that respond to dim light and transmit only shades of gray; the 7 million cones, concentrated largely at the center of the retina in the fovea, react to bright light and are responsible for color vision.
Tiny nerve fibers extend from the rods and cones in all parts of the eye. These come together at the rear of the eyeball to make up the optic nerve, which connects with the brain.
Tests for Dry Eyes
Dry Eye Questionnaire:
More often than not a health professional will treat dry eye syndrome on the basis of the symptoms alone. A widely used Dry Eye Questionnaire (DEQ) has been developed to evaluate dry eye symptoms. It comprises 14 questions that can give a score from 0 to 45. A person who has a score in excess of 14.5 have an 87% sensitivity and specificity for dry eye syndrome. Maximum possible score is 45. The closer a person’s score to 45, the higher the likelihood that they are suffering from dry eye syndrome.
(Adv Exp Med Biol 1998;438:835-8).
The McMonnie & Ho Dry Eye Questionnaire follows:
Do you ever experience any of the following symptoms:
How often do your eyes have these symptoms:
Have you ever had eye drops prescribed or other treatment for dry eyes:
Do you suffer from thyroid abnormality:
Do you suffer from arthritis:
Do you experience dryness of mouth, nose, throat, chest or vagina:
Do you regard your eyes as being unusually sensitive to cigarette smoke, smog, air conditioning or central heating:
Do your eyes become very red and irritated when swimming in chlorinated fresh water:
Do you take the following eye drops or medication:
Or any of these:
Are your eyes dry and irritated the day after drinking alcohol:
Are you known to sleep with your eyes partly open:
Do you have eye irritation when you wake up from sleeping:
This test is used to determine whether the eye produces enough tears to keep it moist. A health profession may administer this test when a patient complains of excessively watery eyes or very dry eyes. The test uses paper strips that are inserted into the eye to measure the production of tears. Tiny slips of filter paper are placed under the lower eye lid or conjunctival sac. The eyes are then closed for five minutes. The paper film is then removed and examined to measure the amount of moisture. Some people find the test to be irritating to the eye. Healthy eyes will produce more than 10 mm of tears in five minutes.
Although Schirmer’s Test has been in use for over a hundred years, it does not identify a large group of patients with dry eyes.
Lactoferrin Assay Test: This test measures the amount of lactoferrin in the tears. This is a sophisticated test which may be done as a follow-up to the Schirmer’s Test.
Fluorescein Eye Drops: Fluorescein eye drops are used to determine the rate of tear production. The drops contain a dye which can be traced by means of as special light as it is washed out of the eye by the patient’s tears.
Symptoms of Dry Eyes
Dry eye syndrome is characterized by general discomfort of the eyes (sandy – gritty irritation). This irritation will get worse as the day progresses. It will be accompanied by itchiness, redness, the feeling that there is a foreign object in the eye (even if there isn’t), discomfort after prolonged periods of eye strain (such as in computer use or sewing) and uncontrolled tearing ( this is a result of the lacrimal gland producing more tears in response to iritataion). Blurry vision, trouble with blinking and light sensitivity may also be present. Smoke will also abnormally upset the eyes.
Diagnosis of Dry Eyes
Diagnosis of dry eye syndrome involves an analysis of the quantity and quality of one’s tears. Patient history is an important aspect of such diagnosis.
The tear break-up test (TBT) is a measure of the amount of time it takes for tears to break up in the eye. Dyes, such as fluorescein or rose Bengal, can also be used to stain the surface of the eye and determine how much it is affected by dryness. The Shirmer test uses a small strip of paper which is inserted in the eye, on the edge of the lower lids. The paper film is then removed and examined to measure the amount of moisture.
Who Gets Dry Eyes?
Dry eye syndrome can affect anyone. However, as one ages the likelihood of developing dry eye syndrome increases. For example, the condition affects about 7 people out of 100 in their 50s but 15 out of 100 in their 70s. This because the rate of tear production decreases as we age.
Dry eye syndrome affects women in greater numbers than it does men. People who are taking certain medications may also develop dry eye syndrome as a side effect to their medication. The following medications may lead to dry eyes;
- Diuretics (water tablets)
- The contraceptive pill
- Such beta blockers as propranolol and atenolol
- Some eye drops used to treat other eye conditions
Dry eye syndrome may also develop out of a more general disease such as rheumatoid arthritis, systemic lupus erythematosus (SLE) and Sjogren’s syndrome. It may also evidence itself as a result of damage to the outer part of the eye caused by injury, disease or surgery.
Lifestyle factors can also lead to dry eye syndrome. The following prolonged activities may put a person at risk for developing dry eye syndrome;
- Prolonged staring at a computer screen
- Long periods of reading without blinking
- Living and working in dry places
- Wearing contact lenses that absorb fluids
- Following a diet that fails to provide sufficient amounts of essential fatty acids or anti-inflammatory foods.
- Droopy eyelids
- Autoimmune disorders like diabetes, arthritis, lupus and Sjogren’s syndrome.
For some people, especially the young, there is no apparent cause for dry eye syndrome.
Lasik and Dry Eyes
LASIK stands for Laser-Assisted In Situ Keratomileusis. It is a surgical procedure intended to reduce a person’s dependency on glasses and contact lenses. It does this by permanently changing the shape of the cornea (the clear covering of the front of the eye). Patients are awake and mobile during the surgery, although they are administered a local sedative. The operation proceeds as follows:
- A corneal suction ring is applied to the eye.
- A microkeratome (laser knife) is used to cut a flap (with a hinge remaining at one end) in the cornea.
- The flap is folded back revealing the stroma (mid-section of the cornea).
- Portions of the stroma are vaporized using a computer controlled laser (excimer laser), thus changing the shape of the cornea.
- The flap is replaced.
Post-operative care for LASIK eye surgery patients involves a course of anti-inflammatory and antibiotic eye drops. Dark goggles are also worn for a period of time as a protection from bright light. Protective shields are also used to prevent the person from rubbing their eyes while sleeping.
All LASIK patients will experience dry eyes to some extent after surgery. Most patients, however, will not notice it to any appreciable degree. Some patients, however, may experience painful dry eyes after LASIK surgery. Those with a pre-existing dry eye problem may find the condition exacerbated. The LASIK surgical procedure creates a thin layer of tissue, which is called a flap. Laser energy is applied under this flap to reshape the cornea in order to correct the patient’s eyesight problem. When the flap is created it is possible that the minute nerves of the cornea may be severed. These nerves are vital to the signaling process that ‘tells’ the lacrimal gland to produce more tears. In time the nerves re-establish themselves. Dry eye syndrome after LASIK surgery, then, is generally a temporary condition. It will usually not last for more than a few months after surgery.
Inflammation and Dry Eyes
Chronic inflammation of the eyes is known as blepharitis. More often than not blepharitis is the underlying condition leading to eye irritation. Symptoms of blepharitis are;
- Redness of the eye
- Tearing of the eye
- Burning and itching of the eye
- Light sensitivity
- A sandy, gritty sensation in the eye (this conditions is worst upon awaking)
Blepharitis is a chronic disease for which there is currently no cure. Long treatment is needed in order to keep the condition under control. There are two phases to treatment; the acute and the maintenance phase. The acute phase involves intensive therapy to bring the condition under control. Maintenance involves a continuing program of the minimum amount of therapy necessary to keep the condition under control.
Many practitioners, especially those of Traditional Chinese Medicine (TCM) believe there is a link between dry eye syndrome and chronic inflammation. Chronic Inflammation is instigated when pro-inflammatory hormones (cytokines, prostaglandins) signal the white blood cells to isolate and clear out antigens, damaged tissue and infected areas of the body. The inflammatory process then moves into high gear, neutralizing and eliminating the intruder and then beginning the healing process. If such inflammation is acute and ebbs and flows according to specific needs, then the immune system is working efficiently. However, sometimes the inflammatory response does not switch off when the danger has passed. This leads to chronic inflammation.
Stress, smoking, high blood sugar levels, bacteria, viruses and parasites are all contributory factors towards chronic inflammation.
The organ that rules the eyes in TCM is the liver and it is the liver that is the organ of detoxification. Improper detoxification leads to inflammation. Although no clinical trials have yet directly linked dry eye syndrome with chronic inflammation, the experience of many practitioners is that excessive inflammation will absorb lubricant s from all over the body – including the eyes.
Menopause and Dry Eyes
Dry Eyes are not one of the symptoms that one would immediately associate with menopause. Yet dry eyes affects as many as 60% of menopausal women – without many of them even realizing that it is connected to the period of natural cessation of menstruation. Many eye disorders are symptomatic of deeper problems within the body. The hormone changes associated with menopause may lead to the decreased tear production that is at the root of dry eye syndrome. An imbalance of the substances that comprise tears may also result in dry eye syndrome. Tears are vital to the correct functioning of the eye because they protect and lubricate the eyes. If dry eye syndrome is left untreated, the eye will become susceptible to increased risk of infection and serious visual impairment.
Dry eye syndrome is more likely in menopausal women who take hormone replacement therapy. Those with arthritis or an auto immune disease are also at greater risk as are those who use eye drops with preservatives in them. Those who eat lost of animal fats and eat plenty of fried foods and dairy products also put themselves in the dry eye syndrome high risk category.
Menopausal women who are affected by dry eye syndrome should implement the following lifestyle changes;
- Eat less meat, fried foods and dairy products
- Eat more chunky white tuna
- Eat more walnuts
- Wear wrap around sunglasses when you are outside
- Avoid (or at least reduce) eye make-up
- Stop using products that can make your eyes dry such as Benadryl, Coricidin, atropine and beta blockers such as Timoptic, Betoptic, Betagan, and Ocupress.
- Blink regularly
- Rearrange your computer so that you are looking down on the monitor
- Avoid smog and fumes
- Quit smoking and try to avoid being around smokers.
Treatments for Dry Eyes
Artificial tears are over the counter eye drops that are used to treat dry eyes. They work by adding volume to the tear film. This can only occur, however, while the film remains in contact with the surface of the eye. Artificial tears require some agent that will allow them to remain in contact with the eye surface. This is called a viscosity enhancing component. Hydrogels are the viscosity enhancing component most commonly used in artificial tears. Artificial tears may also contain glycine, magnesium chloride, and zinc chloride, all of which are found in natural tears. Sodium borate, a mild antiseptic, and other desirable ingredients may also be included.
Despite the addition of viscosity enhancing components, artificial tears still have a relatively short retention time on the eye surface, limiting their effectiveness. Scientists are currently experimenting with ingredients that have some bio-adhesive properties, such as Systane, to lengthen the eye surface contact time.
A wide selection of artificial tears are available. The following guide will help you to select the right type for your condition:
*** Moderately hypotonic artificial tears has been shown to promote ocular surface disease healing in severe dry eyes. Available hypotonic tears include: Thera Tears, Hypotears and Akwa Tears.
(Br J Ophthalmol. 2002 Aug;86(8):879-84, Ophthalmologica. 2001 Mar-Apr;215(2):124-7)
*** Bicarbonate containing artificial tears have been shown to promote healing in severe dry eyes. Available bicarbonate containing tears include: Bion Tears, Murine Tears.
(Arch Ophthalmol. 1995 Mar;113(3):371-8, Cornea. 1993 Mar;12(2):115-20)
*** Oil containing eyedrops (Refresh Endura, Soothe) may be added if meibomian gland dysfunction is present. These eyedrops will replenish the lipid layer of the tear film and prevent tear evaporation.
*** In severe dry eyes and unresponsive surface disease patients have significant visual impairment and disability. In such patients the use of autologus serum eye drops has been shown to help.
.(Br J Ophthalmol. 2004 May;88(5):647-52, Graefes Arch Clin Exp Ophthalmol. 2005 Mar 9)
Punctal occlusion is a medical procedure in which the tear drain of the eye is closed. In the normal course of events, tears leave the eye through two tiny openings in the corners of the eye. A duct runs from there into the nose. In this operation, small plugs are placed in the ducts, forcing the tears to stay on the eye for a longer period of time. Punctal plugs may be made of either collagen or silicon. Collagen plugs are intended to be temporary and will dissolve within a matter of days. Silicon plugs are permanent, though they can easily be removed by a physician.