Objective: To investigate the frequency of dry eye syndrome (DES) in patients with ankylosing spondylitis (AS) by measuring tear osmolarity (TO) with the recently introduced TearLab system (TearLab Corp, San Diego, Calif.) and to determine the relationship between the severity of DE and AS activity.

Materials and Methods: Fifty-seven eyes of 57 patients and 29 healthy individuals as the control group were included. TO measurements, tear break-up time (BUT), and Schirmer’s tests were performed. The patients were divided into three main groups based on their Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) scores: healthy controls, mild-moderate (BASDAI ≤ 4), and severe (BASDAI>4) , into another group based on HLA B27 status: control, HLA B27 (+) and (-), finally based on treatment status: control, treatment (+) and (-).

Results: There were no significant differences based on BASDAI among these subgroups in terms of TO (P= 0.383), BUT (P= 0.722) and Schirmer’s scores (P= 0.108). Also disease activity score values were not correlated with TO values ( r=0,23, P=0,863), Schirmer’s scores (r= –0.223, P= 0.095) and BUT scores (r = –0.044, P= 0.744).

Conclusion: In our study, we determined higher TO values in non-treated, HLA-B27 marker positive and high disease activity groups. Although these values did not reach statistical significance, our findings suggest that in high inflammatory levels, TO can be utilized as a preliminary marker for AS disease activity.