Hyperosmolarity is a well-established fundamental characteristic of dry eye disease (DED).1
When patients have dry eye symptoms, osmolarity testing is a logical step to confirm the diagnosis, but what does it mean when the tear osmolarity test is normal in a patient with symptoms suggesting DED?
In the early days of point-of-care tear osmolarity testing, many practitioners faced with this diagnostic dilemma assumed the test was inaccurate because it went against their clinical judgment. When osmolarity testing disagreed, our early reaction was often that the machine must be wrong. We now know otherwise.
Just as tear osmolarity can help us diagnose DED, it can also help us know when to pause and look for an alternative diagnosis. My colleagues and I conducted a study exploring how osmolarity testing can help make alternate diagnoses in symptomatic patients.
Key to alternate diagnosis
To see how tear osmolarity testing could be used in daily practice, my colleagues and I followed our standard dry eye screening protocol. Patients completed a dry eye questionnaire, and positive answers triggered our technicians to perform dry eye testing, including tear osmolarity (TearLab Osmolarity System, TearLab).
The study group included 50 consecutive patients with normal osmolarity and at least one suggestive symptom of DED, such as ocular irritation, foreign body sensation, itching, dryness, gritty feeling, fluctuating visual acuity, or redness.2
For this study, normal osmolarity was defined as < 308 mOsm/L in both eyes and an inter-eye difference of < 8 mOsm/L.
In all 50 patients, we were able to make an alternate primary diagnosis other than DED, which explained their symptoms (Figure 1). The most common alternate diagnoses were allergic conjunctivitis and anterior blepharitis (each 24%); epithelial basement membrane dystrophy (EBMD, 12%) (Figure 2 on next page); keratoneuralgia (12%); contact lens intolerance (8%); conjunctivochalasis (8%); and computer vision syndrome/situational DED (6%). Less common diagnoses included trichiasis and cyclosporine-A treated DED.