by David A. Wallace, MD
Some patients observe awareness of dry eye symptoms, often in association with contact lens wear, or after laser vision correction care such as LASIK or PRK. There are several reasons why this might be the case, and they do not relate to the surgery in the overwhelming majority of instances. They relate more to our ability to help patients understand the numerous contributing factors to dry eye, and how to manage these in our warm, dry, desert climate. With all vision correction care we endeavor to optimize the ocular surface both before and after surgery, provide careful follow-up care, and attend to numerous details in the process.
The normal cornea is very sensitive to touch, foreign body sensation, and mild superficial injury. Anyone who has ever had an eye infection, contact lens-related irritation or corneal scratch knows this to be true. A network of sensory nerves provides this exquisite sensitivity. If the ocular surface is chemically irritated (by exposure to noxious substances in or near the eye), or otherwise disturbed (mechanical injury, etc.), this can cause the eye or eyes to become irritated, red, and sore. All of these symptoms (irritation, redness, dryness, soreness, and sometimes excess tearing as a reflex to dryness) can be manifestations of ocular surface irritation. In LASIK, creation of the flap causes some of the sensory nerves to be cut, which actually diminishes sensitivity. I tell patients that it is 'as if the phone lines are down;' such that the eye surface cannot convey to the tear gland when additional moisture is needed. Typically, these nerves do grow back, and sensitivity returns to reasonably normal levels within about three months of treatment.
For this reason, we tell all patients that it is very important to use artificial tear eye drops on a very frequent basis for at least first 2 or 3 months after LASIK, and longer if desired to maintain or increase comfort. I advise use of tears as often as every couple of hours through the day, or whenever one remembers to put in a drop. If preservative-free tears are used, there is no hazard to over-use. There are many formulations and brands of artificial tears available. We like and currently recommend Thera-Tears, GenTeal, and Systane among others. If used in a reasonably diligent fashion for the recommended interval, dryness symptoms can be reduced to a manageable minimum, or eliminated.
Lubricant Gel can be a useful adjunct at night before retiring if necessary. We have used GenTeal Gel, Systane Gel and Thera-Tears Liqui-Gel with good success. These products are longer-lasting than eye drops, but the trade-off is that they are a bit too 'goopy' to be useful during the day, when eyes are open. There are several in-between products including Thera tears Liqui-Gel drops, GenTeal "Moderate to Severe" drops and others, which can be used during the day and do not impair visual function as much as the night-time gels.
Climate and environment are very significant influences on eye comfort, and on tear requirements. Ambient temperature and humidity are critical factors. It is my experience that far fewer people complain about dry eyes in regions where the air is moist and cool (such as San Francisco, Seattle or Vancouver), compared to other regions where air quality is hot and dry (Palm Springs, San Bernardino, Bakersfield, Las Vegas, etc.).
Southern California weather is often hot, dry, dusty and sometimes smoggy. When weather conditions include high pressure over the desert, our Santa Ana winds make for particularly warm, windy, dry conditions. Low humidity, wind, warm weather and poor air quality clearly can aggravate symptoms of dry eye and can be the difference between being comfortable or not. There is not necessarily any escape by heading indoors, as virtually all central heating and air conditioning systems also remove moisture from the indoor air. In commercial aircraft, the cabin air is pressurized but is also dehumidified, so I encourage the use of artificial tears as often as every 30 - 45 minutes while in flight (if not asleep).
Moving air and air turbulence are also significant factors affecting eye comfort and wetting. Moving air and turbulence dramatically increase evaporative loss of the water portion of the tear film. Examples include using a hair dryer to style and blow-dry hair, or driving in a convertible with the top down in the desert. Even a slight amount of air movement can have a significant adverse effect upon eye comfort, and it sometimes affords great relief simply to adjust the fins on a vent directing air movement from central heating or air conditioning systems. The same holds true for A/C in a car, where there can be a trade-off between feeling that cool breeze on your face and maintaining good eye comfort. People reading this where the climate is colder should simply substitute "warm" for "cold" and "heating" for "A/C" in the above example.
While I do find it common for post-LASIK patients to have mild dry eye issues, these are typically easily treatable with some combination of the simple steps outlined here. It is with extreme rarity that I encounter any patient manifesting profound dryness or ocular surface disease.
The normal human tear film is about 98% water (with dissolved minerals or "salts" including sodium, potassium and calcium), about 1% lipid (an oily film that reduces evaporation, reduces tear breakup, and helps the lids glide smoothly over the corneal surface), and about 1% mucopolysaccharide (the "mucus" component, long water-soluble molecules that further stabilize the tear film, and promote adherence to the corneal epithelium). The watery portion of human tears are created by a combination of the tear gland and special mucin-secreting cells on the ocular surface.
Maintaining good hygiene, and good hydration, are essential to keeping the eyes comfortable. I recommend that people keep at least six factors in mind to accomplish this:
Collagen punctal plugs placed in upper and lower tear drainage channels
Duration of effect varies from ~2 to 8 weeks
Polymer-treated punctal plugs are the same size, but can last ~6 months
Silicone punctal plugs
Ultrasonic humidifiers - dozens of models are widely available
The eyes, like orchids, need moisture to thrive and be happy!
Helping the eyes maintain their moisture helps in so many ways. Think of your eyes like orchids, which thrive in moist, warm climate; and you will appreciate how simple, and important it is to keep them moist to keep them happy!
The above is an extensive but incomplete list of factors that can cause "dry eye", and a review of suggested remedies. It is our goal that patients achieve excellent vision and optimum eye comfort. Using the above as a guide and reference, we personalize our recommendations to the needs of each patient. With diligence on everyone's part, we are able to treat those patients who are uncomfortable, unhappy, or functionally impaired due to ocular surface symptoms including dry eye.