Artificial Tears – Why and How?
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 symptoms of eye surface dryness are not serious; however, they are annoying and irritating. Although it sounds contradictory, the most common cause of sudden watering and tearing is evaporation of the “tear film” – momentarily creating dry regions on the surface of the cornea. 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 UV light. 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 across the eye surface – much like the wipers on our car windshield during a drizzle. The cornea is one of the most sensitive parts of our body and the reason is to stimulate blinking as either a protective reflex or to keep it from becoming too dry.
With age, the quality of the tear film diminishes, and it tends to evaporate more easily. Microscopic dry spots form and these exposed areas on 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, taking a shower does not lubricate dry skin, but instead washes off the natural skin oils. Water is wet but paradoxically makes our skin surface 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 a medical necessity, artificial tears 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, artificial tears are a slightly oily liquid that lubricates (rather than rinses) the eye surface. Some patients use them four times a day, such as during mealtimes and once in the afternoon. Because the eyelids will be closed during sleep, using artificial tears immediately before bedtime is less helpful.
For occasional use, 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. Most 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. Therefore, if one frequently uses artificial tears, it is preferable to use unpreserved tears to avoid potential irritation from excessive amounts of this chemical preservative. Systane Complete is a popular brand of long-lasting, unpreserved tear. If it momentarily blurs the eyesight too much, one can try or alternate it with Systane Hydration. Both come in bottles without preservatives.
Using unpreserved artificial tears is a good idea during the first several months after cataract surgery, when the eye can be more sensitive. Cataract surgery performed 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 aware of symptoms shortly after surgery.
In addition to improving comfort, artificial tears may also enhance your vision. Your eye functions like a camera, and the clear cornea is the very front part of this camera. This explains why a dry cornea may also cause your eyesight to vary. Instilling an artificial tear and blinking is akin to having a Zamboni resurfacing the ice rink. The surface immediately becomes smoother and clearer. After cataract surgery if one’s vision tends to vary a lot – some days clearer and other times blurrier – it would not be caused by the artificial lens implant. Instead, variable drying of the cornea surface is a common cause.
Typically, most patients find relief by using artificial tears 3 – 4 times daily. Analogous to watering a brown lawn, it may take 1-2 weeks of regular artificial tear use before improvement is noticed. At that point, one can try reducing the frequency to twice-a-day. Likewise, artificial tears may not eliminate all symptoms, but rather should make them less frequent and more tolerable. Patients with more severe dryness may benefit from instilling lubricating ointment into the eye at bedtime. These come in a tiny tube and are found in the same over-the-counter section as artificial tears at every pharmacy. Lubricating ointment moisturizes the cornea surface better than using artificial tears alone. 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 regularly if your symptoms are not significant.