Tear Osmolarity Explained

How the “Saltiness” of Your Tears Tells a Story


Tear osmolarity is the saltiness of your tears. As the moisture in the tears dries up, the salt remains behind, making the tears more concentrated. The first published report of a correlation between tear osmolarity (TO) and dry eye disease (DED) was in 1981. In the years since then, there has been much research into this correlation. The research has consistently found a high correlation between TO and DED. In fact, in mild to moderate dry eye, TO has a higher correlation with DED than any other test currently available.

In the two main types of dry eye, evaporative and aqueous deficient, TO is usually elevated and/or asymmetrical between the eyes. Studies find about a 90% accuracy of tear osmolarity testing in diagnosing dry eye.

There are two common instruments used in-office to measure TO. The accuracy and reliability of both instruments are supported by the literature. The procedure is very simple and painless and quickly obtains a measurement of the patients TO. Because it is important to compare the reading from one eye with the other, it is imperative to measure the TO of both eyes. As with many medical tests, the results can vary from one day to another, so it is sometimes valuable to repeat the test looking for variability. This variability itself is an indicator of an unstable tear film and therefore an important clue in diagnosing dry eye.


TearLab Osmolarity Testing Unit

iPen Osmolarity Testing Unit

Tear osmolarity testing is currently the most accurate way to assess dry eye in the earliest stages, often leading to a quicker diagnosis. When the tear osmolarity is high, there is usually damage already on the surface of the eye. For this reason, early detection is key to help prevent damage to the eye.

The TO readings can also be used by your eye doctor to monitor the effectiveness of your dry eye treatment. If your treatment plan is correct and you are diligent in following it, tear osmolarity should decrease over time.

Our network doctors are excited to have these tools available to help diagnose and manage dry eye disease in our patients.