Dry Eye Syndrome

Dry eye is a condition that affects millions of people. The medical term for dry eyes is Keratoconjunctivitis sicca. Dry eye can range from a mild condition to a sight-threatening disability. It may be associated with illnesses such as rheumatoid arthritis and Sjogren’s syndrome. Fortunately, the understanding and treatment modalities for dry eyes have improved dramatically over the last decade.

Dry eyes are one of the most common reasons for a visit to the doctors at EDOW. Our doctors specialize in this condition and are involved with research to assist in its diagnosis and management.

Causes of Dry Eyes

Dry eye affects up to 15% of the adult population in the United States. It is more common in women and increases with age. The hormonal changes that occur during menopause are felt to affect tear secretion.

While one thinks of tears as “water,” in reality tears have a complex structure with three major components. Think of the tear film as a thick sandwich with a thin stabilizing layer of lipid on one side and mucin on the other side. In between these two layers is a salty mixture of water.

The lipid layer is on the outer surface of tears. The lipid layer is composed of oils. The Lipid layer plays a vital role in stabilizing tears. The lipids allow the tears to spread uniformly across the surface of the eye as well as reduce the rate at which tears evaporate. If the lipid layer is removed, tears will evaporate at 19 times the normal rate, and the eye will become parched.

The aqueous layer is the "middle layer" of tears. The aqueous layer is the main component of tears and is composed of water mixed with electrolytes, such as salt. The concentration of the electrolytes needs to be in balance (“isotonic”) with the underlying cells on the corneal and conjunctival surface.

The mucin layer is the inner portion of the tear film. The mucin layer allows the tears to adhere to the underlying cells on the surface of the eye (conjunctiva and cornea). The structure of the tear film is demonstrated on the slide below:

The aqueous (water) component of tears is produced by two different sets of lacrimal glands. Under normal conditions, the accessory lacrimal glands located in the upper and lower lids (see diagram below) produce the tears necessary to keep the eye moist. This is called “basal tear secretion” or your constant tears. When the eye is irritated, the main lacrimal gland located in the upper/outer portion of the orbit produces a flow of tears. This is called “reflex tear production.” When tears flow from the main lacrimal gland during reflex tear production, an excessive amount of tears is produced creating watery eyes.

When someone has dry eyes, there is almost always insufficient basal tear flow. The main lacrimal gland will then start to produce tears. Since the flow from the main lacrimal gland is usually too great, a common complaint from patients with mild dry eyes is actually “watery eyes.” It always seems paradoxical to patients when we explain that their watery eyes are caused by insufficient tear production. This is why it is important to understand the relative function of the two lacrimal glands – main (reflex tears) and accessory (basal tears).

Because we all live under varying environmental conditions, our level of tear production must vary to accommodate the circumstances. The two main methods to stimulate tear production are:

1. Nerve innervation
2. Hormones

Androgen hormones assist with the stimulation of tear production. As people mature, especially women, the changes in hormonal balance have an effect on tear production. Unfortunately, the use of traditional oral hormone replacement therapy has not demonstrated substantial efficacy in the treatment of dry eyes in women. It may also be associated with other illnesses such as a higher incidence of breast cancer.

There is a neural loop (see diagram below) between the surface of the eye and the lacrimal glands. When the ocular surface is irritated, a nerve impulse is sent from the surface of the eye to the brain. The signal is then sent on to the lacrimal gland. Once this message reaches the lacrimal gland, more tears are stimulated.

A substantial amount of ocular surface irritation can inhibit the eye’s ability to send a message to the brain to create more tears. This creates a vicious cycle in which the eye becomes irritated and, therefore, less nervous stimulus is sent to the brain creating less of a signal to create tears.

There are many causes of dry eyes; however, the most common causes are age and environmental conditions. With the aging process, the hormonal changes play a major role in the prevalence of this condition in mature women. There is also a mild reduction in nerve stimulation with the aging process. Conditions that may exacerbate dry eyes include the following:

• Environmental stresses such as low humidity, cigarette or cigar smoke, and air pollution can irritate the eyes. In the winter and summer, heaters and air conditioners tend to reduce moisture in the environment.
• Allergies and air pollution may increase ocular surface irritation that affects the neuronal loop that stimulates basal tear production. Computer terminals – when we stare at a computer terminal for a long period of time, the rate at which we blink our eyes tends to be reduced, causing ocular surface irritation.
• Medications – certain medications especially those used for depression and allergies may cause a reduction in tear production. You should check with your physician if you use drugs for any of the following conditions:
• Allergies
• Breast Cancer
• Depression
• Parkinson’s Disease
• Incontinence
• High Blood Pressure
• Soft Contact Lenses – almost all soft contact lenses have water as a major constituent. The lens will act as a sponge on the ocular surface to maintain the appropriate water content.

Certain medical conditions are associated with dry eyes. These include collagen vascular disorders such as Rheumatoid Arthritis, Lupus, and Sjogren’s syndrome. These conditions affect the immune system and may cause an immune-mediated inflammation in the eye. Non-immune-related diseases may also affect dry eyes. Parkinson’s disease causes a poor or incomplete blink response. This may dry the ocular surface. Herpes Zoster (“Shingles”) and Bells Palsy affect the neural loop and may also cause dry eyes.

Treatment of Dry Eyes

Tear substitutes

The most common treatment for dry eyes is tear supplementation. There are a variety of tears available for patients. No one brand of tears is ideal for every patient. The type and frequency of tear supplementation varies depending on several factors:

1. Severity of dry eyes
2. Environmental conditions (temperature and humidity)
3. Medications
4. Activities (such as staring at computer screens)

As the severity of dry eye condition progresses, tear supplementation needs to be more frequent. It is important to realize that there is "no magic number" for the number of times that each patient should use tears each day. If someone lived in a constant environment, like a space ship, with identical environmental conditions each day (temperature, wind and humidity), then a fairly consistent tear regimen could be established. Unfortunately, in the Washington metropolitan region, the weather fluctuates on a regular basis. In the winter and summer, when forced dry heat or air conditioning is needed; tear supplementation needs to be more frequent. The doctors at EDOW usually recommend a range for the frequency of tear supplementation (i.e. 2-4 times/day or 4-6 times/day, etc). We suggest that patients take an active role in adjusting their tear frequency based upon the variables discussed above.

Of equal importance is understanding that tears should be used proactively rather than reactively. If you have a lawn, you do not wait until it turns brown and then water it. You water it so it stays green and healthy. In our hectic world, patients often forget to use their tears on a regular basis. They often wait until their eyes hurt, and then use tears when their eyes hurt. This behavior is repeated all day long. If you wait until your eyes are uncomfortable, the dryness is causing damage and inflammation to the ocular surface. It takes more tears to heal a damaged surface than maintain a healthy surface. Once a patient establishes a regular regimen, the need for tears actually diminishes since the ocular surface is healthier.

One helpful hint is for patients who use computers all day to place a timer on the compute. This reminds them to use tears on a regular basis

There are a variety of types of tears. They are categorized below:

1. Preservative Free Tears: Most tear supplements come in a bottle. Once the bottle is opened, there is concern about contamination with microorganism. Bacteria may contaminate and colonize within the tear bottle leading to infection. To minimize the risk of bacteria, preservatives are placed into the tear bottles to eliminate bacterial growth. When tears are used on a frequent basis (greater than 4 times/day), the preservatives placed into the tears bottles can be toxic to the ocular surface.

   To avoid this toxic effect, preservative free tears were developed for patients who need to use tears frequently. These tears are delivered from small individual packets. The tear packets can be used for more than once per day; however, they should not be used once open for greater than 12 hours.

   Preservative free tears come in a variety of formulations. They contain nutrients to heal and maintain the ocular surface. They may also contain substances to thicken the tear film. Thicker (viscous) tears are helpful in conditions where the tear film is unstable; however, the viscous agents such as methylcellulose can blur vision as well as from a coating on contact lenses.

   • Non-viscous tears. These "thin" tears have minimal viscous agents. Some of the tear brands include: Bion, Refresh, Refresh Plus, Theratears, and Tears Naturale PF.
   • Medium Viscosity tears. These tears contain methyl cellulose (or other thickening agents) as well as electrolytes. Some of the brands include Endura, Refresh Plus, and Theratears.
   • Viscous tears: These include higher concentrations of methylcellulose and are usually limited to eye conditions where the ocular surface is irregular or very unstable. They are also used at bedtime for greater protection while sleeping. Brands include Celluvisc and Occucoat.
   
   

2. Dissolving Preservative Tears: This type of tear product is relatively new. These tear bottles have a special type of preservative that becomes inactive when the tear comes in contact with the environment (either oxygen or light). These types of tears have the benefits of being able to be dosed on a frequent basis (more than 4 times/day) while maintaining the convenience and cost of being dispensed in bottle form.

   • Non-viscous tears. These tears are similar to the preservative free tears. Some of the brands include Refresh and Genteal.
   • Viscous tears. These tears have a higher concentration of gels to thicken and stabilize the tears. Brands include Refresh Liquidgel and Genteal Medium).
   
   
3. Preservative Tears: These types of tear products are available in bottles. This makes them less expensive and convenient. Tears with preservatives should be limited to no more than four times per day. A variety of companies make tears containing preservatives. Some of these brands include Systaine and Tears Naturale II.

Restasis

Restasis, the first medication specifically indicated to increase tear production and reduce inflammation was approved by the US FDA last year. Restasis is created from cyclosporine, an anti-inflammatory immunomodulating drug. In clinical trials, 60% of patients produced more tears. There was also clinically significant improvement in patient symptoms and ocular irritation.

Restasis is available as a drop that is used twice a day. The drug takes several months to be fully effective. The doctors at EDOW have had great success with this medication. Dr. Clinch and Dr. Kang has been an invited lecturer to teach other physicians on the clinical applications of the medication.

Punctal Occlusion

Tears are removed from the ocular surface through a specialized lacrimal drainage system. (See below). There are two drainage systems present in each eye. They are located in the upper and lower lid. The opening to the drainage system is called the puncta. Closing one or both puncta decreases the rate at which tears can drain from the ocular surface. Punctal occlusion can reduce the frequency of tear supplementation as well as improve dry eye symptoms.

There are two methods to close the lacrimal drainage system. The doctors at EDOW perform these procedures on a daily basis.

• Punctal Plugs:
  Plugs made out of a collagen or silicon can be inserted into the drainage system. The procedure is brief (2-3 minutes) and painless. The silicon plugs do not dissolve and can remain in place for years. Punctal plug placement is a reversible procedure. If excessive tearing occurs, the plugs can be removed. Since dry eyes are a medical condition, insurance companies should provide coverage for this service.
  
  

  		Punctal plug
  		Insertion of a punctal plug
  		Punctal plug in place

  
  
• Punctal Cautery:
  The lacrimal drainage system can be permanently closed with heat. The punctal region is first anesthetized; heat is then used to seal the punctal opening. This procedure is brief (2-3 minutes) and performed in our offices on a regular basis. Since dry eyes is a medical condition, insurance companies should provide coverage for this service.

Oral Supplements

Oral supplements of omega-3 essential fatty acids may be of assistance in managing dry eyes. Daily dietary supplementation has been shown in scientific studies to do the following:

• improve the oil and aqueous (water) layers of the tears
• suppress ocular irritation

Omega-3s are essential fatty acids. "Essential" fatty acids means that these chemicals cannot be produced by our body. They must be ingested as part of our diet. The two best sources of omega-3s are dark, oily, cold-water fish, and flaxseed. These essential fatty acids have been established to provide a multitude of health benefits. Surprisingly, up to 83% of Americans may be deficient in omega-3s.

Dietary supplementation with essential fatty acids is available by many companies. Theratears Nutrition and HydroEyes are two brands that have been utilized by the doctors at EDOW.