What do variations in readings between eyes in the same patient mean?
The ability to mitigate environmental stress via compensatory mechanisms will vary from eye to eye within the same patient, thus resulting in variations in the osmolarity readings. As dry eye disease progresses, osmolarity readings may vary from eye to eye, with at least one eye in the abnormal range. Patients with dry eye disease (hyperosmolarity) have a dysfunctional tear film, combined with poor homeostatic osmoregulatory capability. As such, stress on the tear film causes instability that is not seen in normal tear film. This is demonstrated in the table below, in which four consecutive TearLab osmolarity measurements are made one-minute apart over three days in both a dry eye and normal patient. * As seen below, the dry eye patient has wide fluctuations in tear osmolarity, eye-to-eye, test-to-test and day-to-day, attributed to the pathological instability of the tear film, while the normal patient shows no variability beyond the expected analytical variability of the instrument it
