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Which Dry Eye Tests Are Best?

Contact Lens Spectrum January 1, 1999

Discovering dry eye

Which Dry Eye Tests Are Best?

BY KELLY A. KINNEY, OD, MS
JANUARY 1999

Decreased wear time, discontinuation of lens wear and dryness or grittiness with contact lenses are some familiar complaints of dry eye syndrome, but we often rely on tests to help us diagnose the condition eye?

condition. The first step in evaluating the worth of any test is to establish test repeatability. Of equal importance is test validity. There's no accepted gold standard dry eye diagnostic test, so we can evaluate validity only in comparison to existing tests which may or may not be accurate.

Defining Repeatability

Test repeatability is most often evaluated by performing the test on two occasions in a sample of patients. The test procedures should be as close to identical as possible between visits, and the time between retest visits should be short enough to minimize disease fluctuation. Large differences between test visits can indicate poor repeatability, disease status fluctuation or both.

There are a variety of statistics we can use to evaluate repeatability, but the most common are the Kappa statistic, used as a chance-corrected measure of agreement for ordinal data (i.e., fluorescein staining grades 0 - 4), and the 95% limits of agreement, used for continuous data (i.e., tear break-up time and the Schirmer test).

Repeatability Investigation

A recent study at the Ohio State University College of Optometry evaluated the repeatability of clinical diagnostic tests for dry eye on a sample of 75 dry eye patients. Most (84%) repeat visits in the study were performed within one week. Table 1 lists the results.

TABLE 1
Repeatability results for common clinical dry eye tests
TEST REPEATABILITY MEASURE INTERPRETATION RESULT
McMonnies (-7.76 points, 8.58 points) up to an 8-point difference can be found between visits Fair (?) repeatability
Tear break-up time (-6.39 sec to 6.72) up to an 7-point difference can be found between visits Fair to good repeatability
Schirmer's test (-19.90 mm to 11.49 mm) up to an 20mm difference can be found between visits Poor repeatability
Tear meniscus height measurement (-0.21 mm to 0.30 mm) up to an 0.3mm difference can be found between visits Fair (?) repeatability
Phenol red thread test (-15.50 mm to 13.8 mm) up to an 16mm difference can be found between visits Poor repeatability
Corneal fluorescein staining k = 0.25 A k result of 0.9 is excellent Poor repeatability
Corneal/conjunctival rose bengal staining k = 0.21 Does this indicate fluctuation Poor repeatability

We often think of dry eye as a chronic disorder, but it might be better characterized as a chronic fluctuating disorder, which could partially explain the poor repeatability of many of the diagnostic tests we use. There are a few notable test results, such as tear break-up time (good repeatability) and the Schirmer test (poor repeatability), as well as a few with diagnostic potential -- McMonnies' questionnaire and tear meniscus height measurement.

Don't Forget to Listen

Abnormal test results are more likely to lead to a dry eye diagnosis, but normal results don't always rule it out. Be sure to listen to patient symptoms and address the signs accordingly.

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