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How many times have you heard complaints from your patients about burning, stinging or itchy eyes?
Before you as the clinician get the chance to seat such a patient behind a slit lamp or thrill him or her with Shirmer strips, chances are you are already thinking about a diagnosis of dry eye. To support this pre-diagnosis, all you need is objective clinical evidence.
Yet, herein is where the problem lies.
Quest for a better way
In many patients, dry eye is the diagnosis of choice, but the limited and objective clinical evidence remains inconclusive.
The literature indicated that tear hyperosmolarity was the main source of ocular surface inflammation, damage, and symptoms, which initiated tear compensatory mechanisms.3 The evidence was compelling that tear osmolarity was likely the universal component and a key diagnostic biomarker for DED.
The importance of tear osmolarity
From their work on the tear film, Tomlinson, et al. concluded:
The measurement of tear osmolarity arguably offers the best means of capturing, in a single parameter, the balance of input and output of the lacrimal system. It is clear from the comparison of the diagnostic efficiency of various tests for keratoconjuctivitis sicca (KCS), used singly or in combination, that osmolarity provides a powerful tool in the diagnosis of KCS and has the potential for being accepted as the gold standard for the disease.4
Abnormal tear osmolarity is a failure of homeostatic osmolarity regulation. The higher the osmolarity, the more severe the dry eye. Historically, literature suggested a 316 mOsms/L cut-off for more moderate-to-severe disease.5
However, based on the results of a 300-patient trial, presented at the 2009 annual meeting American Academy of Ophthalmology, osmolarity was found to have 88% specificity, 75% sensitivity in mild/moderate disease and 95% sensitivity in severe disease at a diagnostic cut-off of 308 mOsms/L.6
Therefore, osmolarity values above 308 mOsms/L are generally indicative of dry-eye disease. Clinicians should examine all points of subjective and objective data and not rely only on cut-off values because they are only guidelines.
It is important to note that this study demonstrated that TearLab outperformed both Schirmer's testing and corneal staining with respect to the sensitivity and specificity in patients with the mild-to-moderate DED.6
Understanding and interpreting osmolarity results in the clinical setting was critical to proper diagnosis of our patients. It is well understood that DED is usually of gradual onset and progression, especially in the early stages when full expression of markers may be intermittent or missing.7
Below are some key observations for mildly symptomatic patients with tear osmolarity in the 308 to 316 mOsms/L range:
Combining the quantitative osmolarity scale (275 to 400 mOsms/L) with a qualitative range of severity makes it easier to visualize and communicate to patients. The diagram was placed in each exam room.