Understanding Dry Eyes & Dry Eye Syndrome
Reviewed by Marc Michelson, M.D.
Dry Eyes or Dry Eye Syndrome is a very common eye condition that affects millions of Americans. It is estimated that dry eyes affect up to 11% of people aged 30 to 60 years of age and 15% of those 65 years of age or older according to the International Task Force assembled by the Johns Hopkins University-Wilmer Eye Institute. They also concluded that as many as 12 million Americans have moderate to severe dry eyes and that this number is likely to increase with the aging populations resulting in a significant decrease in the quality of life.
Simply, dry eyes are caused by either a deficiency in the quantity or the quality of the tears or tear film. Fortunately, today eye care patients can benefit from better diagnostic procedures for dry eyes as well as more advanced dry eye treatments from eye physicians.
About Tears & the Tear Film
Understanding the structure of tears is important in order to understand how the tears and tear film provide the eye with a number specialized functions. Tears are composed of three layers. The innermost layer is called the mucus layer. The mucous layer acts to coat the cornea with a smooth layer of lubricating material called mucin. The mucous layer serves to provide a surface that allows the tear film to stick to the eye. The middle layer of the tear film is called the aqueous layer, and as the name implies is composed primarily of water. In fact, it is composed of about 98% water and serves to provide moisture, oxygen and nutrients to the cornea. The outermost layer of the tear film is called the lipid layer. The lipid layer is actually an oily film that acts to prevent evaporation of the tear film from the eye. A deficiency in any one or more of the tear film layers can lead to dry eyes. Eye physicians can use specialized diagnostic tests to determine which layers of the tear film are contributing to the dry eye symptoms.
Tears are produced by a number of different gland structures around the eye. The innermost layer, the mucous layer, and the outermost layer, the oily layer are produced by tiny tubular shaped glands that are in the eyelids. The middle layer, the aqueous layer, is produced by the lacrimal gland which is a structure located just under the upper eyelid. Each time you blink, the eyelids act like squeegee to smooth and spread the tear film so that it is uniform across the surface of the cornea. This smoothing of a normal tear film creates a high quality optical surface. In some cases of dry eye, the tear film is deficient enough that the eyelids cannot provide a smooth optical surface and patients then experience blurry vision that clears with repeated blinking.
Normally, excess tears flow out of the eye along the lower eyelid toward the nose and into two tiny ducts called lacrimal puncta. The lacrimal puncta open into small tube like canals that drain into the nasal passage. As a result of this connection between the drainage of tears from the eye and the nasal passage, often times when we cry we may actually experience a runny nose. Usually tears are produced on a continual basis in order to lubricate the eye. And maintain the crisp optical surface of the cornea. Reflex tears are also produced in response to pain, trauma or even an emotional event. Reflex tears tend to be overly watery and do not to alleviate a dry eye or even the symptoms of a dry eye. There are may causes of dry eye syndrome. As a result of the normal aging process it is common to experience dry eyes. In general, as we age our body produces less oil to lubricate the skin and skin like tissues. In fact, on average we produce 60% less oil at age 65 than we do when we are 18. Women tend to have drier skin in general so this is considerably more noticeable to them. As discussed previously, production of the oily layer of the tear film serves and important role in preventing the evaporation of tears. Without a healthy and sufficient oily layer it is likely that there will be excess evaporation resulting in dry spots on the cornea, blurry vision and a sensation of dryness.
There are many other factors that can contribute to dry eyes. These include being exposed to hot, dry, windy climates for example as well as poor air quality from pollution or cigarette smoke. Dry eye symptoms are often associated with prolonged computer use or intense reading due to the decrease in the frequency of blinking with these activities.
It is extremely common for contact lens wearers to experience dry eye syndrome due to the fact that contact lens materials tend to absorb tears and protein from the tears creating dry spots on the lens surface.
Finally, dry eyes are a frequent side effect of many systemic medications, medical conditions such as Thyroid disease, Parkinson’s Disease and Sjorgren’s Syndrome and Vitamin A Deficiency. Most women report experience dry eyes as they enter menopause due to the hormonal changes they encounter, particularly changes in estrogen.
Symptoms of Dry Eye Syndrome
The most common symptoms of dry eyes include dryness, itching, burning, irritation or grittiness, redness, blurry vision that gets clearer as you blink, light sensitivity and contrary to common sense….excessive tearing. These symptoms typically increase during vision related activities such as reading, computer use, night driving, or watching television. They may also increase in response to environmental conditions such as wind, low humidity, airplane travel, or smoking or being in a smokey environment. Many of these symptoms of dry eyes may also be found in other eye conditions, making careful diagnosis especially important.
What are the causes of dry eye syndrome?
Environment: Sunny, dry, or windy weather, heaters, air conditioners, and arid high altitudes increase the evaporation of tears from the surface of your eyes. You may experience dry eye symptoms while viewing television, computer screens, while reading or doing anything that reduces your rate of blinking.
Aging: During the normal aging process, our bodies and our eyes produce gradually less and less oil. This reduction in oil in the tear film results in quicker evaporation leading to the formation of dry spots on our eyes.
Contact Lenses: Contact Lenses are subject to dehydration or loss of their water content. As they dehydrate, they can absorb the tear film causing dry eye symptoms. In some cases, the continued drying of the contact lens surface causes it to become deposited with protein making the lenses even more uncomfortable than the dryness alone.
Medical Conditions: Women experiencing hormonal changes, those patients suffering from thyroid disease, rheumatoid arthritis, psoriasis, eczema, acne rosacea and a number of other systemic conditions may experience dry eye syndrome.
Medications: Diuretics taken for high blood pressure, allergy medication, antihistamines, acne medications and many others may all produce dry eye symptoms.
How do I know if I have dry eye syndrome?
Common symptoms of dry eyes may include dryness, burning and stinging. A foreign body sensation, like sand being in the eye, is often encountered. Your vision can be blurred. Reflex tearing may actually be stimulated resulting in excessively watery eyes. Some patients may experience redness of their eyes. It is not uncommon for your eyes to lose their normal luster and clearness when looking in the mirror.
To help you determine whether you suffer from one or more symptoms of dry eyes you can take a brief self assessment quiz for dry eyes.
Diagnosis of Dry Eyes
There are several clinical examination methods that are useful for helping to diagnose and determine the severity of dry eyes. Your eye doctor may use all or some of the following tests to help make the diagnosis:
Tear Break Up Time is a measurement made by observing the rate at which the tear film begins to evaporate and indicates the overall stability of the tear film.
Tear Staining is a method of using special dyes to help highlight problems with the surface of the eye and the tear film quality. By placing these eye drops in the tear film the severity of the dryness can more easily be recognized.
Tear Film Height is a measurement made with the slit lamp biomicroscope to evaluate tear volume
A Schirmer Test may be performed by placing a small piece of special paper inside your lower eyelid to measure tear production.
From these tests an assessment can be made as to whether the dry eye condition is mild, moderate or severe and thus what type of treatment options may be best.
Treatment of Dry Eyes
For those patients with mild to moderate dry eyes the first course of treatment may be to use unpreserved artificial tears as prescribed by the doctor. Depending on the nature of your tear film deficiency, the doctor may have you use a specific type of artificial tear that has different characteristics in terms of salt content and viscosity. Follow these instructions carefully. In addition, your doctor may counsel you on environmental factors that need to be modified. Sometimes, if the oily layer of the tear film is deficient, they may suggest that you increase your consumption of oily fish or even take flax seed oil as a dietary supplement. Most likely you will be asked to drink plenty of water.
For patients with mild, moderate or severe dry eyes, who may already be using artificial tears and already have punctal plugs without relief, the prescription of Restasis eye drops in addition to the other treatments can often help alleviate your symptoms. Restasis works by suppressing a type of inflammatory cell from entering the Lacrimal Gland and thus allows the lacrimal gland to function more effectively so that you can actually make more of your own natural tears. A clinical study published by Drs. Perry, Solomon and Donnenfeld in the August 2008 edition of Archives of Ophthalmology concluded that the use of Restasis® eye drops (cyclosporine) may alleviate the signs and symptoms of dry eye during all stages of dry eye disease and especially in patients with mild forms of the problem. The study results for mildly affected patients suggest that the earlier the treatment with Restasis®, the better the overall treatment results.
If these approaches do not work, the eye doctor will likely suggest the insertion of tiny punctual plugs that will slow down or even stop the drainage of tears from the eye. These plugs are easily and comfortably placed in the lacrimal puncta in the eyelids. Initially you may have a temporary dissolving plug put in place to see if your signs and symptoms are actually responsive to this treatment. If the results are good, it may be necessary to place a more permanent type of plug in the lacrimal puncta to affect a long-term solution. Occasionally there are some cases that may not respond to the above sequence of treatment options because of some underlying low-grade inflammatory or infectious process. In these cases it may be necessary to also prescribe an oral antibiotic such as a tetracycline or an anti-inflammatory eye drop such as a corticosteroid eye drop.
As you can see, the diagnosis and treatment of dry eyes is complex and requires patience and persistence on the part of the physician and the patient. With careful diagnosis and a systematic therapeutic approach, sufferers of dry eye syndrome can most often experience considerable improvement.
You may to take a short dry eyes quiz to learn more.