discovering dry eye
Using the Dry Eye Tools We Have
BY BARBARA FINK, OD, FAAO
Dry eye is difficult to treat because we are still learning about its etiology and only beginning to develop treatments specific to these causes. Dry eye is difficult to diagnose because we have many definitions of dry eye, and all of them include symptoms which are difficult to measure. Many methods for diagnosing dry eye involve tools not available to most eyecare practitioners, such as osmometry, tear protein analysis, meibometry, meniscometry and evaporimetry. How can we use the tools that are available to us to correctly diagnose dry eye?
Sequencing of Tests
It is generally thought that the diagnosis of dry eye depends on the results of several tests. It would be most convenient for the patient if all these tests could be performed at a single visit. However, the performance of one test could affect the results of subsequent tests; therefore, tests should be carried out in an appropriate order. There is not a lot of data available to provide evidence as to which tests might influence other tests, but it seems reasonable to assume that more invasive tests should be performed after less invasive tests.
Because most experts agree that dry eye is associated with symptoms of ocular discomfort, symptom questionnaires have been developed. Questionnaires ask about various symptoms of dry eye, as well as about symptoms that may be related to environments, medications, systemic health, contact lens wear and eye drop use. A positive answer to "Do your eyes feel dry?" or "Do you think you have dry eye?" provides the best indication that therapy should be considered.
Minimally Invasive Tests
Minimally invasive tests, such as obtaining measurements of the tear meniscus height, should be performed next. Measure the tear meniscus height at the slit lamp by setting the slit width to 1mm and comparing the tear meniscus height to the slit width. A tear meniscus height of less than 0.3mm might indicate reduced tear secretion.
Tear break-up tests and fluorescein staining of the bulbar conjunctiva and cornea are slightly more invasive. Non-invasive break-up times (without fluorescein) are longer than fluorescein break-up times. Tests of tear volume or secretion should be performed after break-up tests because they involve contact with the tears by solid substances.
The Schirmer Test has been used for a long time and is one test that helps to determine a deficiency of tears. If a patient shows less than 5mm of wetting in five minutes without anesthetic, then the patient probably has a problem with insufficient tearing. However, problems with this test include the fact that the greatest wetting occurs during the first minute, and the results are not reproducible and are affected by time of day and frequency of testing. The reluctance to discard the Schirmer test in clinical practice may be due in part to the fact that it is simple to use, fast and inexpensive. The phenol red thread test is very similar. It takes less time and causes less irritation; however, it absorbs tears from the cul-de-sac, and the size of the cul-de-sac affects test results.
More Invasive Tests
The final tests that can be performed in attempting to diagnose dry eye and its cause are rose bengal or lissamine green staining, followed by assessment of the meibomian glands.
Using the tools we have in the correct order can help diagnose and classify dry eye. As additional tools and treatments become available, we will be able to prescribe managements that are specific to the causes of dry eye.
Dr. Fink is an associate professor at The Ohio State University and a principal investigator for the CLEK clinic.