Osmolarity is a measure of particles in a solution. Tear film osmolarity tests the concentration of salt in the tear film. The higher the concentration, the less water and thus the “drier” the eye.
There is some debate as to the usefulness of tear film osmolarity testing in the diagnosis of Dry Eye symptoms.
Reference
What is the Value of Incorporating Tear Osmolarity Measurement in Assessing Patient Response to Therapy in Dry Eye Disease?
Francisco Amparo, Yiping Jin, Pedram Hamrah, Debra A. Schaumberg, Reza Dana
American Journal of Ophthalmology
Volume 157, Issue 1, Pages 69–77.e2 DOI: http://dx.doi.org/10.1016/j.ajo.2013.07.019
View the full report