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Get Clarity on Tear Osmolarity

Here’s how new technology can help achieve an accurate dry eye disease diagnosis and ultimately get patients relief.

DAVID ELDRIDGE, O.D., F.A.A.O., TULSA, OKLA.

The accurate diagnosis of dry eye disease (DED) in your patients is crucial to their quality of life and ocular health, as well as your practice’s financial wellbeing. Not properly identifying these patients and effectively treating their DED can cause contact lens dropouts and the loss of patients to other eyecare practitioners.

Accurate DED identification via the traditional DED diagnostic tests can be challenging because DED symptoms and signs do not always correlate. For example, a patient may have normal Schirmer’s test results but have ocular surface staining consistent with the DED diagnosis.

The good news: Several new diagnostic tests are available to accurately identify DED early in the disease process, as well as determine severity levels. One of these tests is the TearLab Osmolarity System, from TearLab. (See “Other DED Tests,” page 31.)

Here, I discuss how it can diagnose DED and how to incorporate it into your DED testing.

Too much salt?

Tear osmolarity is a primary marker for DED, says the “2007 Report of the International Dry Eye Workshop (DEWS).” Thus, an elevation in tear osmolarity, or hyperosmolarity, reveals patients at risk of physiologic damage or a patient with poorly controlled DED. Tears should remain in homeostasis, and normal subjects present with low and stable osmolarity. As patients begin to lose this balance of homeostasis and the osmolarity increases, tear film instability is seen as well as inter-eye differences: More than 7mOsml/L to 8mOsml/L between eyes has been shown as a hallmark of DED.

Tear osmolarity, along with other clinical assets, such as the slit lamp exam and your clinical experience, allows you to determine whether the patient has DED and to what extent, which directs the management protocol. The System is comprised of a Reader (a small countertop device), Pens and disposable Test Cards. To perform the test, you, or a technician, insert the test card onto the Pen, place the Pen on the tear meniscus of each eye to automatically collect the tear fluid sample (50 nL), and replace the Pen in the Reader, which then displays the patient’s tear osmolarity in less than 8 seconds. (See “Reimbursement,” left.)

Normal tear osmolarity is equivalent to normal blood osmolarity, which averages between 280mOsms/L and 300mOsms/L. A study including 314 subjects using the DEWS severity scale and tear osmolarity, reported in the American Journal of Ophthalmology 2011, showed mild DED beginning at 308mOsml/L, an overlap of mild to moderate between 308mOsml/L to 328mOsml/L and severe as greater than 328mOsml/L.

In-office implementation

This is the first opportunity for many eye doctors to use a point-of-care lab test, and it is imperative to perform basic quality control (QC) tests to ensure accurate results in your testing. (A QC program is included in the initial in-service.)

To successfully employ tear osmolarity in your practice, follow these four steps:

1 Provide a DED symptom questionnaire to all patients. More than a dozen of such questionnaires exist, including the Dry Eye Questionnaire, the Ocular Surface Disease Index and the Impact of Dry Eye on Everyday Living questionnaire. Many of your DED suspects will be elderly patients, contact lens wearers and post-refractive surgery patients.

2 Have a protocol in place for the staff to know when it is indicated to obtain tear osmolarity tests. If the questionnaire you use indicates the patient may have ocular surface disease (OSD), the protocol can allow patients to be tested upstream before you see the patient. Having the lab results in hand when you examine the patient allows you to better “rule in or rule out” DED. (Remember: This is a lab test, not a procedure, as the former is used to assist in the diagnosis while the latter is employed to document a diagnosis already confirmed.) A less efficient alternative is to re-schedule the patient for a follow-up exam at which you obtain the osmolarity.

3 You make the diagnosis, and there is no “magic number.” No test is 100% correct, and your training allows the use of multiple inputs to make a correct diagnosis. Using other tests, e.g. TBUT, staining, etc., in addition to having a physiologic marker, makes you more accurate and allows patient management through time using a number, just as we do with glaucoma.

Following your determination of evaporative, aqueous or a combination of the two, discuss a treatment plan with the patient. If the patient reports DED symptoms but has normal tear osmolarity, consider other conditions/diseases, such as conjunctival chalasis, ocular allergy and/or epithelial basement membrane dystrophy.

4 Schedule follow-up visits. Acquire subsequent tear osmolarity readings along with other necessary tests. Having an osmolarity “number” is helpful for you to gauge therapy response and to document treatment efficacy and compliance. Patients respond positively to a specific number, rather than to foreign terms, such as “staining” or “tear break-up time.” As the System is a lab test, there are no “frequency limitations” for tests performed. As long as you are managing the patient and feel it is medically indicated, document this in the patient’s chart. This allows your staff to know if/when you want the test performed upon the patient’s return to the clinic.

Efficient intervention

The fact that signs and symptoms often don’t correlate should not concern us as much. With new technology advancements and other clinical assets, we can achieve an accurate and efficient DED diagnosis and get these patients relief. OM

Dr. Eldridge is the vice president of Clinical Affairs & Professional Development at TearLab, the maker of the TearLab Osmolarity System. Send comments to optometricmanagement@gmail.com.