Dry eye syndrome is one of the most common conditions treated by an ocular expert. It is estimated that over ten million Americans suffer from dry eyes. Dry eyes are usually caused by a deficiency in the amount or quality of the tear film that covers and lubricates the eyes.
Tears are comprised of three layers
- Layer One
The most inner layer that is closest to the eye is the mucus layer. The mucous layercoats the cornea, the clear window of the eye. The mucous layer serves as a foundation that allows the tear film to adhere to the surface of the eye. The mucous layer comes from tiny mucin glands on the surface of the eye. The mucous layer is sticky and stringy.
- Layer Two
The middle layer is known as the aqueous layer. The aqueous layer is derived from the lacrimal gland, also knwon as the tear gland. The aqueous layerprovides moisture to the eye and facilitates oxygen transfer from the air to the cornea. This aqueous layer is composed mainly ofwater. The aqueous layer also has a small amount of salt, proteins, antibodies to fight infection,and other nutrients.
- Layer Three
The outer layer of the tear film that covers the aqueous layer is composed primarily of fats or lipids. This is an oily layer that helps prevent evaporation. The lipids that compose the outer layer are derived from meibomian glands that are located near the base of the eyelashes.
The aqueous portion of the tear film is formed as part of a process known as lacrimation.The aqueous layer is produced by the lacrimal gland that is located under the outer corner of the upper eyelids. As we blink, the tear film is spread evenly across the surface of the eye. Tears flow from the outer portion of the eye towards two tiny drainage ducts in the corner of the eye by the nose.The opening of these ducts is known as the lacrimal punctum. The tear ducts leads to a small reservoir of fluid beneath the inner corner of the lower eyelids known as the lacrimal sac. The lacrimal sac leads to a canal that drains into the nasal passage. The connection between the tear ducts and the nasal passage is the reason that crying causes a watery nose.
Function of tear film
The surface of the eye has mucous membranes and a cornea that depend on a wet surface to prevent drying (dessication). Drying of the surface of the eye causes it to break down and the eye becomes very uncomfortable. The tear film carries antibodies to ward off infection. The tear film also carries dirt and debris from the eye away from the eye and into the nose. A healthy tear film is essential for maintaining clear vision.
Causes of Dry Eyes
There are many reasons for dry eye syndrome. The most common reason is related to the normal aging process. As we grow older, our eyelids produce less mucin and oil. The production of oil is partially regulated by hormones. The influence of hormones on dry eyes is believed to be a significant factor in women, who tend to have eye dryness to a larger extent than in men. Deficiencies in the production or quality of oil on the surface of the eye leads to quicker evaporation of the tear film.
External factors may also influence the tear film. The tear film is affected by hot weather, dry or windy climates, and air conditioning. All of these conditions tend to increase dryness of the eyes. Cigarette smoke and dusty environments irritate the eyes and cause increase the tearing reflex. Individuals who are intently involved with reading or computer work have a reduced rate of blinking. The “windshield wiper” effect of blinking is reduced when blinking is less. When this happens, the distribution of tears is negatively affected, causing dry spots to form on the surface of the eye. Periodic blinking when performing concentrated work helps to prevent drying of the eyes.
Contact lenses may exacerbate dry eye syndrome because contacts absorb the tear film from the surface of the eye. This is more common with soft contact lenses than with either gas permeable or hard contact lenses. There are new types of contact lenses that have reduced absorption of the tear film. Certain medications such as those for reducing bladder dysfunction or those that dry the skin may exacerabate dry eye syndrome. Thyroid dysfunction and certain diseases such as Parkinson’s and Sjogren syndrome may be associated with dry eye syndrome. Nutritional factors may also influence the tear film. For example, vitamin A deficiency is known to exacerbate eye dryness, but flaxseed oil in your diet is believed to improve symptoms of eye dryness.
Symptoms of dry eye syndrome
- Chronic irritation
- Blurred vision that improves with blinking
- Periodic excessive tearing that attempts to compensate for dryness
- Increased discomfort after periods of reading, working on a computer, or watching television
Eye examination by an ocular expert is important for detecting dry eye syndrome. The tear film in patients with dry eye syndrome tends to break down into dry spots quicker than usual. When the tear film becomes excessively dry, small erosions develop in the cornea. These microabrasions of the cornea are referred to a punctate keratitis. The production of tear fluid may be determined by a simple test known as a Schirmer tear test. The Schirmer tear test is a rudimentary measurement that may be helpful in affirming dry eye syndrome. However, it is a rather imprecise test. Special eyedrops may be helpful to confirm the presence and extent of dry eyes.
The most common form of treatment of dry eyes is to simply replace lack of moisture with lubricating eyedrops. There are many types of over-the-counter lubricating eyedrops available. Many patients find that one or two drops during the day is sufficient. Some patients may only need to use lubricating eyedrops on very hotor dry days. Some patients may only need to use lubricating drops when working for prolonged periods of time in an air conditioned office.
Some lubricating eyedrops are watery and alleviate symptoms temporarily. Other types of lubricating drops are thicker and adhere to the eye longer, providing longer intervals of relief. The disadvantage of thicker eyedrops is that they may blur your vision for aperiod of time. Even though the blurriness may be very short, the altered vision can be disturbing to some individuals. Preservative-free lubriating eyedrops are often recommended for individuals who use eyedrops on a frequent basis. This is because preservative-free eyedrops have fewer preservatives that may sensitize and irritate the eye with prlonged use. Eyedrops that whiten the eyes do not necessarily have lubricating properties, and may actually make the eyes dryer.
Special drops to rejuvenate that natural tear gland are also available. These eyedrops are meant to be used twice a day for as long as the dry eye syndrome persists. These eyedrops are not meant for everyone with dry eye syndrome. An eye examination may determine of you are a suitable candidate for these prescription eyedrops.
Another method for treating dry eye syndrome involves closure the the tear duct with a special insert called a punctal plug. A punctal plug works like closing a sink drain with a stopper. The closed tear duct drain prevent the exit of tears and allows the eye to retain moisture. Closure of the tear duct opening may be done with temporary dissolvable collagen plugs, or by a long lasting silicone plugs. The downside to silicone plugs is that they may spontaneously extrude or become dislodged causing eye irritation. When this happens, the punctal plugs need to be replaced. A simple cauterization of the tear duct opening is another option that may be considered to achieve closure of the tear duct opening without the use of punctal plugs.
The diagnosis of dry eye syndrome by an ocular expert is made by history and ocular examination. Patients are presented with various options for treatment for their dry eyes and with informed discussion, we determine the best approach to treating this common problem.
Case in Point
Dr. Reynard was retained to evaluate severe dry eyes in a patient following lasik eye surgery who also had polycystic ovarian dysfunction.