The Contribution Of Tear Osmolarity Measurement To Ocular Surface Assessment In Contact Lens Wearers

Purpose: To determine whether tear osmolarity using the TearLabTM Osmolarity System contributes to the assessment of the ocular surface in contact lens (CL) wearers. Methods: Data were collected from 44 CL wearers (28 tolerant and 16 intolerant) and 34 healthy subjects. Every patient underwent a thorough ophthalmic examination and tear osmolarity test, conjunctival impression cytology and meibomian lipid sampling. Symptoms, break-up time (BUT), tear osmolarity, conjunctival expression of HLA-DR and meibomian fatty acid composition were evaluated. Results: Tear osmolarity was significantly higher in the controls compared to tolerant and intolerant CL wearers (p=0.0007). Flow cytometry results expressed in antibody-binding capacity (ABC) units and percentage of positive cells revealed a significant difference between intolerant CL wearers group and control group (p<0.0001). Furthermore, comparisons between tolerant and intolerant CL wearers showed only a significant difference for mean fluorescence levels expressed in ABC (p<0.0001). Moreover, impression cytology analysis showed similar values in the tolerant CL wearers and the control group. Material of CL (hydrogel) was significantly correlated with the percentage of positive cells both in tolerant and intolerant CL wearers. BUT was significantly shorter in intolerant and tolerant CL wearers subjects than in healthy subjects (p<0.0001), whereas there was no significant difference in meibomian fatty acid composition (p=0.98) between groups. Conclusions: CL wear is responsible for ocular surface alterations whose patterns are very similar to those reported in dry eye syndrome. However, the yield of tear osmolarity with TearLabTM in assessing ocular surface disorders in CL wearers deserves further investigation.