This study evaluated commonly used biomarkers in dry eye disease management and found that, over a three-month period, tear film osmolarity had the lowest variability among them. Reductions in osmolarity preceded changes in symptoms during therapy with cyclosporine. Osmolarity was the only sign sensitive enough to reveal changes in tear physiology and to reduce its variation after treatment.
Bilateral tear osmolarity, Schirmer, tear film breakup time (TBUT), staining, meibomian grading, and Ocular Surface Disease Index (OSDI) were measured over a three-month period in participants recruited from a clinic-based population at two locations. Tear osmolarity was measured with the TearLab Osmolarity System made by TearLab Corp. (San Diego), which provided support for this study and in which some of the study's authors have financial interests.
Fifty-two subjects with mild, moderate or severe dry eye completed the study. After the observation period, severe dry eye patients were prescribed topical cyclosporine A and evaluated for an additional three months.
Tear osmolarity exhibited significantly less variability over the three-month period than corneal staining, conjunctival staining and meibomian grading across the entire patient population. Osmolarity also demonstrated less variation than TBUT, Schirmer tests and OSDI, although these differences were not significant. Variation in osmolarity was less for mild dry eye patients than severe dry eye patients.
After treatment, average osmolarity and variability decreased significantly and symptoms, as measured by OSDI, showed a decreasing trend. None of the other signs demonstrated a change after treatment.
The authors suspect that mild/moderate dry eye patients may benefit from cyclosporine A treatment. They say that the relative insensitivity of Schirmer strips may have prevented physicians from observing the positive therapeutic effect of cyclosporine in less severe dry eye patients. They suggest, based on the current study, that the use of osmolarity could serve as a competent predictor of symptomatic response in these patients.
The authors conclude that these data indicate that efficacious dry eye therapy should achieve a stable low tear film osmolarity, and also support the hypothesis that hyperosmolarity is aligned with primary dry eye disease mechanisms, such as chronic inflammation.