Why concentration matters
Healthy tears have a stable concentration close to that of blood. When the oil layer fails and tears evaporate faster, or when the lacrimal gland produces less, the tears that remain become saltier. That hyperosmolarity is itself harmful: it stresses the cells of the corneal surface, triggers inflammation and damages the goblet cells, feeding the cycle that makes dry eye chronic. Osmolarity is therefore both a marker of dry eye and one of its mechanisms.
The test
A small pen-like device with a disposable tip touches the tear meniscus at the outer edge of the lower eyelid and draws up a sample a fraction of a drop in size. The tip is placed in a reader and the result appears within seconds. Both eyes are tested, because the variability between them is itself a sign of an unstable tear film. No anesthetic is needed and there is no discomfort.
Reading the result
Values below about 308 milliosmoles per liter with the two eyes within a few units are normal. Higher values indicate dry eye, with the severity rising with the number; values above 320 are moderate and above 340 severe. A difference of eight or more between the eyes is abnormal even if both values are in range. The result is read alongside the tear film break-up time, gland imaging and the inflammation test, which together identify the cause.
Tracking treatment
Osmolarity falls as the tear film stabilizes, and repeating the test at follow-up gives a number that shows improvement independent of how the patient feels on the day. Before laser or lens surgery, a normal osmolarity is one indication that the surface is ready for accurate measurement.
Is this right for your eyes?
Nothing on this page is a diagnosis. Whether this is the right choice for you is decided by a full examination at one of our 4 offices: Pasadena, Huntington Beach, Woodland Hills and Beverly Hills.
About this content: This page was written with the assistance of AI tools and reviewed for medical accuracy by Dr. Bavand Youssefzadeh, DO. It is general information, not medical advice, and does not replace an eye examination. Individual results vary. Read our medical disclaimer.
