By David F. Chang MD
Many patients over the age of 55 complain that their eyes occasionally water, burn, itch, or feel scratchy or heavy. These dry eye symptoms are not serious; however, they are annoying and irritating. Although it sounds contradictory, the most common cause of sudden watering and tearing is an “unstable tear film” – momentarily producing a dry eye surface. When we are awake, our upper and lower eyelids only cover part of the eyeball surface. The rest of the surface is exposed to the environment all day long. Potential irritants include dust, pollen, smog, smoke, wind, and sunlight. Protecting our exposed eye surface from these elements is a thin layer of oily fluid, called the tear film. This also lubricates the eye surface (much like saliva does for our mouth). The purpose of blinking is to constantly spread a fresh tear film over the eye surface.
With age, the quality of the tear film diminishes and it tends to evaporate more easily. Small dry spots form, and these exposed areas of the eye surface become slightly irritated. This may cause a reflex watering to occur. These watery, runny tears rinse the eye surface, but do not lubricate it. As an analogy, water rinses our mouth, but does not coat and lubricate the inside of our mouth in the way that saliva does. Likewise, taking a shower does not lubricate dry skin, but instead washes off the natural skin oils. Water is wet, but makes our skin even drier.
An unstable tear film explains why watering may suddenly occur during certain activities. Evaporation more readily occurs in windy outdoor environments, and with air currents caused by fans and vents. Activities that cause us to stare, such as reading and driving, may cause momentary evaporation of the tear film and reflex watering. None of these activities or situations is harmful; they are merely associated with momentary irritation in eyes with a weak tear film. Other symptoms of a poor tear film include occasional redness, burning, itching, and a sandy or scratchy feeling.
Although treatment is not of medical importance or necessity, artificial tears can provide some relief. These are over-the-counter drops that lubricate the eye and augment our natural tear film. They contain no medicine and are available without a prescription. Unlike water, they lubricate rather than rinse the eye surface. They are usually used up to four times a day, and are best instilled immediately before or after activities that provoke the watering (e.g. outdoor exercise, prolonged reading, etc). Because the eyelids will be closed, using artificial tears immediately before bedtime is not necessary. There is no one superior brand among the dozen or so that are available on the drugstore shelf. Like choosing a soap or shampoo, patients can follow their own preferences.
All bottles of eye drops contain a small amount of chemical, called a preservative. This prevents germs from growing inside the bottle during the weeks after the original seal is opened. If one averages four or more drops of artificial tears daily, it is preferable to use unpreserved tears to avoid potential irritation from excessive amounts of this chemical preservative. Unpreserved artificial tears are more expensive since they require disposable packaging. These tiny vials contain a small number of drops that will be used up within a day or two, and therefore do not require a preservative inside.
It is not unusual for patients to experience the symptoms of a dry eye or unstable tear film during the initial months following cataract surgery. Surgery within the interior of the eye cannot cause the outside surface to become permanently drier. However, some people over the age of 55 already have a dry eye tendency and may first become more aware of it after their surgery. This is because the surface area around the microscopic cataract incision must be kept especially well lubricated during the first several months in order for the eye to feel comfortable. The cataract incision is very tiny – like a microscopic paper cut – but because the lid is constantly rubbing against it with blinking, extra surface lubrication is needed for maximal comfort. If they lack a good tear film, patients may temporarily experience some irritation and scratchiness with blinking, or sudden reflex tearing as described above.
Immediately after cataract surgery, the frequently instilled eye drop medications provide supplemental lubrication. Therefore, the more likely time to experience dry eye symptoms is after the postoperative drop medications have been tapered down. If you experience these symptoms, or have a known dry eye tendency, you should consider using artificial tears liberally for the first few months after cataract surgery to improve comfort. Typically, most patients find relief by using artificial tears 3 – 4 times daily. Analogous to watering a dry lawn, it may take 1-2 weeks of regular artificial tear use before improvement is noticed. Likewise, artificial tears may not eliminate all symptoms, but rather should make them more tolerable and much less frequent. Finally, you should be reassured that mild dry eye symptoms are common over the age of 55. This is not a serious condition and will not result in eye damage. Use artificial tears if you experience discomfort, but you need not bother using them if you have no significant symptoms.