discovering dry eye
Using the Tear Film to Predict Lens-Related Discomfort
BY KELLY K. NICHOLS, OD, MPH, PHD
We've all had contact lens patients who've discontinued contact lens wear. Unraveling the reasons can prove clinically challenging. Over the past few months, we've discussed several theories related to contact lens comfort including lens wettability, lipid components in the tear film and contact lens hydration/water content evaporation.
The fact is that we really don't know what factors have the greatest impact on contact lens comfort. Contact lens factors such as material, Dk/t and water content certainly are important. Patient factors including concurrent ocular surface disease, medication use and systemic disease play a role. Tear film lipids, mucins and the interaction of these tear film parameters are also significant.
Clinically, we know that these factors impact contact lens tolerance. What's most important is helping patients achieve adequate comfortable wear time.
Even successful contact lens patients occasionally experience dryness and/or contact lens irritation. Clinically, it's important to differentiate between the "successful" wearer who has occasional irritation and the wearer who's approaching contact lens discontinuation. In general, successful wearers can wear lenses for nine or more hours (Begley et al, 2000). The most frequent symptoms that lens wearers report are dryness and discomfort, especially at the end of the day. Examining a patient in the afternoon or inquiring about end-of-the-day symptoms can help diagnose contact lens-related dry eye.
More important, if a patient reports that he stopped wearing his lenses, then you should delve into reasons to determine whether discomfort or patient motivation played a larger role. You'd manage a successful patient who thought contact lenses were too burdensome differently than you would an unsuccessful but motivated patient.
Tolerance vs. Intolerance
Glasson et al (2003) performed multiple clinical tests and protein analyses on both successful contact lens wearers and on patients who had discontinued contact lens wear because of discomfort. They evaluated symptoms and performed clinical tests after at least one day of non-lens wear. The authors found significantly reduced tear volume, measured by tear meniscus height, phenol red thread test and noninvasive tear break-up time, in intolerant wearers. Intolerant patients also reported more symptoms than did tolerant patients (based on McMonnies Questionnaire). Tolerant patients reported on average one symptom during non- lens wear, while intolerant patients reported three symptoms.
The authors concluded that evaluating symptoms and dry eye clinical tests before contact lens fitting can help predict intolerant contact lens wearers.
Let Your Patients Decide
"Adequate" is in the eye of the beholder. Some patients are willing to limit wear time to a few hours or during special activities if they have tear film parameters that are in the abnormal range at contact lens fitting. Don't overlook assessing and recording a patient's motivation to wear contact lenses in the fitting process.
In addition, you can improve comfortable wearing time by recommending rewetting drops, care systems that minimize solution sensitivity or more frequent lens replacement. While science is important in contact lens wear, it can't replace the art of contact lens fitting.
To obtain references for this article, please visit http://www.clspectrum.com/references.asp and click on document #108.
Dr. Nichols is assistant professor of clinical optometry at The Ohio State University College of Optometry in the area of dry eye research.