Dry eye syndrome (DES) is an eye disease characterised by eye dryness which is caused by either decreased tear production or increased tear evaporation. In this definition, the term, tear deficiency, implies a deficiency of aqueous tears secreted by the lacrimal gland. It is a multifactorial disease of the tears and the ocular surface that results in discomfort, visual disturbance, and tear film instability with potential damage to the ocular surface.
The medical name for dry eye syndrome is keratoconjunctivitis sicca (KCS) and may be subdivided into 2 main forms.
- Dry eye syndrome associated with Sjögren syndrome
- Dry eye syndrome unassociated with Sjögren syndrome
There are two main types of dry eye.
- Eyes not producing enough tears. For a long time, doctors believed this was the main culprit.
- Poor tear quality, often referred to as evaporative dry eye. This is far more prevalent, accounting for the majority cases.
Many people have both problems.
How Common Is Dry Eye Syndrome?
Dry eye syndrome is very common with approximately 20% of the Australian adult population suffering from dry eyes.
Research suggests that up to 48% of office workers could experience dry eyes, due to their long exposure to air-conditioning and computer screens.
Other groups more likely to report dry eyes include:
- Older adults.
- Post-menopausal and pregnant women.
- Diabetes, rheumatoid arthritis or autoimmune disorders such as lupus sufferers.
- People on Medications such as the contraceptive pill, anti-histamines, tricyclic antidepressants, topical and systemic beta-blockers and topical non-steroidal anti-inflammatory agents.
- Individuals who wear contact lenses.
How Are Tears Produced
Normally, the eye constantly bathes itself in tears by producing tears at a slow and steady rate. In this way the eye stays moist and comfortable.
The eye uses two different methods to produce tears
- tears are made at a slow, steady rate to maintain eye lubrication
- an excess of tears are produced in response to eye irritation or emotion.
The tear film consists of three layers
- an outer oily (lipid) layer
- a watery (aqueous) middle layer
- an inner layer of mucus
Each layer has its own purpose.
The oily layer, produced by the meibomian glands, forms the outermost surface of the tear film. Its main purpose is to smoothe the tear surface and reduce evaporation of tears. Evaporative dry eye occurs when meibomian glands, located in the upper and lower eye lids, don't produce enough oil, or the oil isn't of high quality. This causes the watery layer of the tears to evaporate more quickly.
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 layer functions 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 inner layer consists of mucus produced by the conjunctiva. Mucus allows the watery layer to spread evenly over the surface of the eye and helps the eye remain moist. Without mucus, tears would not stick to the eye.
With each blink of the eyelids, tears are spread across the front surface of the eye, known as the cornea. Tears provide lubrication, reduce the risk of eye infection, wash away foreign matter, and keep the surface of the eyes smooth and clear. Excess tears in the eyes flow into small drainage ducts, in the inner corners of the eyelids, which drain to the back of the nose.
What Are the Causes of Dry Eye Syndrome?
Aging
Dry eye syndrome has many causes. One of the most common reasons for dryness is simply the normal aging process that is associated with less oil production. This is more pronounced in women. The oil deficiency affects the tear film. Without as much oil to seal the watery layer, the tear film evaporates much faster, leaving dry areas on the cornea.
Reduced corneal sensation
Tear secretion also may be reduced by certain conditions that decrease corneal sensation. Diseases such as diabetes and herpes zoster are associated with decreased corneal sensation as is long-term wear of contact lenses and surgery that involves making incisions in or removing tissue from the cornea (such as LASIK).
Medications
A wide variety of common medications, both prescription and over-the-counter, can cause dry eye by reducing tear secretion:
- Beta-blockers for heart or high blood pressure
- Antihistamines for allergies
- Sleeping pills
- Anti-anxiety medications
- Pain relievers
- Diuretics for high blood pressure
Since these medications are often necessary, the dry eye condition may have to be tolerated or treated with eye drops called artificial tears.
Hormonal changes
Dry eye syndrome not associated with Sjögren's syndromeis mostly found in postmenopausal women, women who are pregnant, women who are taking oral contraceptives, or women who are on hormone replacement therapy (especially estrogen-only pills). The common denominator is a decrease in androgens, either from reduced ovarian function (in postmenopausal women) or from increased levels of the sex hormone–binding globulin (in women who are pregnant or are taking birth control pills).
Environmental factors
Other causes for dry eye include exposure to a dry, windy climate or smoke or air conditioning, which can speed tear evaporation. Avoiding these irritants can offer dry eye relief.
Autoimmune disorders
Patients with primary Sjögren syndrome have evidence of a systemic autoimmune disease, as manifested by the presence of serum autoantibodies and severe aqueous tear deficiency (ATD) and dry mouth (xerostomia). Secondary Sjögren syndrome is defined as dry eye syndrome that is associated with a diagnosable connective tissue disorder, which is most commonly rheumatoid arthritis but could also be systemic lupus erythematosus or systemic sclerosis.
What Are the Symptoms of Dry Eye?
Dry-eye sufferers may find that they feel like they cannot keep their eyes open for very long. They may also find their eyes feel more uncomfortable after reading or watching television. Other symptoms include:
- Stinging or burning eyes
- Foreign-body sensation and ocular dryness and grittiness
- Mucoid discharge
- Excessive eye irritation from smoke or wind
- Discomfort when wearing contact lenses
- Photophobia
- Fluctuating or blurry vision
- Excess tearing
While it may seem contradictory, people with dry eye may find that their eyes water quite a bit. This is because their eyes are responding to the irritation of this condition. Because individuals who work long hours at a computer are less likely to blink often, they are more susceptible to getting dry eye than others who do not spend long periods in front of a computer monitor.
How Is Dry Eye Diagnosed?
Dry eye is essentially a clinical diagnosis, made by combining information obtained from the history and from the physical examination and performing one or more tests to provide some objectivity to the diagnosis.
No single test is sufficiently specific to permit an absolute diagnosis of DES.
Symptom questionnaires can be used to help establish a diagnosis of DES and to assess the effects of treatments or to grade disease severity.
Schirmer test
The Schirmer test is used to test aqueous tear production. Traditionally, the basic secretion test is performed by instilling a topical anesthetic and then placing a thin strip of filter paper under the lower eyelid. The patients’ eyes are then closed for 5 minutes, and the amount of wetting in the paper strip is measured. Less than 5 mm of wetting is abnormal.
Tear breakup time
Tear breakup time (TBUT) is determined by measuring the time lapse between instillation of fluorescein and appearance of the first dry spots on the cornea. Measure it prior to instillation of any anesthetic eye drops. A fluorescein strip is moistened with saline and applied under the lower eyelid. After several blinks, the tear film is examined using a broad-beam of slit lamp with a blue filter for the appearance of the first dry spots on the cornea. Decreased TBUT of less than 10 seconds is considered abnormal, indicative of tear instability.
Epithelial staining
Epitheliopathy is a general term for diseases of the epithelium, the surface layer of cells of the cornea. From the patient's perspective, it causes blurred vision. Rose bengal, lissamine green, and fluorescein staining are used to evaluate epitheliopathy. Rose bengal and lissamine green stain not only dead and devitalized cells but also healthy cells that are protected inadequately by a mucin coating. Fluorescein pools in epithelial erosions and stains exposed basement membrane; generally, it stains the cornea more than the conjunctiva.
InflammaDry®
Approved by the FDA in 2013, InflammaDry® is the first and only, rapid, in-office test that detects MMP-9, an inflammatory marker that is consistently elevated in the tears of patients with dry eye disease. The test, which takes less than 2 minutes to perform, uses tear samples to detect the inflammatory marker matrix metalloproteinase-9. Matrix metalloproteinase-9 has been shown to be consistently elevated in the tears of patients with dry eye disease.
What Are the Treatment Options for Dry Eye?
Early detection and aggressive treatment of dry eye syndrome is intended to prevent corneal ulcers, scarring and visual loss.
Artificial tears
The two most common methods of dry eye treatment are to replace tears or to conserve them. In most cases, artificial tears are used as tear replacement, which mimic the composition of natural tears, and are available over the counter.
People with dry eye are often more likely to experience the side effects of eye medications, including artificial tears. For example, the preservatives in certain eye drops and artificial tear preparations can irritate the eye. These patients may need special, preservative-free artificial tears. Lubricating ointments can be used for more severe cases, but they tend to blur vision and so should be applied at bedtime.
Punctal plugs
If artificial tear drops do not relieve the symptoms, tears may be conserved by plugging the tear drain holes, called puncta, with tiny plugs made of collagen or silicone. In the worst cases, the holes can be closed permanently using electric cauterization.
Topical or systemic omega-3 fatty acids
The essential omega-3 fatty acids, such as eicosapentaenoic acid (EPA) and docosahexanoic acid (DHA) found in fish oil and alpha-linoleic acid (ALA) in flax seed oil, are also thought to improve evaporative dry eye. Omega-3 fatty acids are believed to competitively inhibit the production of proinflammatory mediators, such as interleukin-1 and tumor necrosis factor-alpha. With fewer proinflammatory compounds available, the ocular tear film is thought to be able to better promote a healthy ocular surface. A higher intake of omega-3 fatty acids has been associated with a decreased incidence of dry eye syndrome in women.
Topical cyclosporine (Restasis®)
Restasis® Ophthalmic Emulsion is a prescription eye drop indicated to increase tear production which may be reduced by inflammation on the eye surface in patients with dry eye.11, 12 It has been reported that Restasis® works both as an immune system modulator and as an anti-inflammatory drug. Unfortunately, Restasis® is not listed on Australia's Pharmaceutical Benefits Scheme, however some trials are being conducted and access is available for those on these trials.
What is evaporative dry eye?
Evaporative dry eye is caused by blockages in the meibomian glands, which create the lipid (oil) layer of the tear film and are located in the eyelids. This condition of obstructed glands leads to insufficient tear film oil. An insufficient oil layer can cause tears to evaporate four to six times faster than normal. More than 65% of patients suffering from dry eye syndrome have evaporative dry eye. LipiFlow® is intended to treat patients with blocked meibomian glands, called meibomian gland dysfunction, by unblocking the glands and allowing them to resume the secretion of oily lipids needed for a healthy tear film.
What causes evaporative dry eye?
Hormonal changes in women during menopause, particularly decreasing levels of estrogen, can cause thickening of the oils secreted by the meibomian glands, which results in blockages. Decreased estrogen levels may enhance conditions under which staphylococcal bacteria can proliferate in meibomian glands. This results in a decreased oil secretion rate. Additional factors that may cause or exacerbate meibomian gland dysfunction include age, contact lens use and hygiene, cosmetic use, and illnesses, particularly diabetes.
LipiFlow® for evaporative dry eye
Lipiflow is a non-invasive, in-office treatment that takes only minutes to complete for each eye, as both eyes are normally affected by dry eye. During the procedure, the doctor applies controlled heat to the inner eyelid and mild intermittent pressure to release lipids from blocked glands, treating both the upper and lower lid simultaneously
References
- Lemp MA. Report of the National Eye Institute/Industry workshop on clinical trials in dry eyes. CLAO J 1995;21:221-32.
- Foster CS. Dry Eye Syndrome. Medscape.http://emedicine.medscape.com/article/1210417-overview.Updated: 16 Dec 2013. Accessed 2 June 2014.
- Dry Eye Syndrome (Keratoconjunctivitis Sicca). Myvmc.com. http://www.myvmc.com/diseases/dry-eye-syndrome-keratoconjunctivitis-sicca/ Updated 13 March, 2014. Accessed 2 June 2014.
- Boyd K. What is dry eye? Geteyesmart.org. http://www.geteyesmart.org/eyesmart/diseases/dry-eye/index.cfm. Published 1 March 2014. Accessed 2 June 2014.
- Sabhlok S. The remedy or cure for terrible eye pain and eye strain (from excessive computer use). Cure eye strain from computer use. http://eyestrain.sabhlokcity.com/ Published 22 April 2012. Accessed 2 June 2014.
- Foster CS. Dry Eye Syndrome Medscape. http://emedicine.medscape.com/article/1210417-overviewUpdated: 16 Dec 2013. Accessed 2 June 2014.
- Kuo F. Dry Eye Syndrome. Drugs.com. http://www.drugs.com/health-guide/dry-eye-syndrome.html Updated 5 May 2014. Accessed 2 June 2014.
- Chotikavanich S, de Paiva CS, Li de Q, et al. Production and activity of matrix metalloproteinase-9 on the ocular surface increase in dysfunctional tear syndrome. Invest Ophthalmol Vis Sci. 2009 Jul;50(7):3203-9.
- Miljanovic B, Trivedi KA, Dana MR, et al. Relation between dietary n-3 and n-6 fatty acids and clinically diagnosed dry eye syndrome in women. Am J Clin Nutr. 2005;82:887-893.
- Barber LD, Pflugfelder SC, Tauber J, Foulks GN. Phase III safety evaluation of cyclosporine 0.1% ophthalmic emulsion administered twice daily to dry eye disease patients for up to 3 years. Ophthalmology. Oct 2005;112(10):1790-4.
- Stonecipher K, Perry HD, Gross RH, Kerney DL. The impact of topical cyclosporine A emulsion 0.05% on the outcomes of patients with keratoconjunctivitis sicca. Curr Med Res Opin. Jul 2005;21(7):1057-63.
- LipiFlow®. UC Berkeley Optometry. http://www.caleyecare.org/lipiflow. Published 2014. Accessed 2 June 2014.
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