AbstractPurpose: The aim of the study was to evaluate the presence of alterations in the tear film osmolarity and in other parameters that can define the OSD in POAG/OH patients treated with different topical therapies in order to better define the role of osmolarimetry in the clinical management of patients in a real life setting.Methods: This is a cross‐sectional, observational study. All patients with POAG/OH treated with topical medications and 20 subjects age and sex matched as a control group, were consecutively and prospectively enrolled. The following exams were performed: tear film osmolarity assessed using Tearlab®, tear break‐up time (TBUT), corneal staining score (Oxford scale), ocular symptom assessment using Ocular Surface Disease Index (OSDI) questionnaire. These data were compared between POAG/OH patients and control group and correlations were analysed between tear film osmolarity and other DED parameters.Results: 50 POAG/OH patients (25 M/25F; mean age 69 ± 17y) and 20 controls, matched for age and sex, were enrolled. The mean treatment duration was 2.5 ± 1.2 years. Benzalkonium chloride (BAK) was used in 92% of cases. The mean osmolarity value (mOsms/L) in POAG/OH patients was 306 ± 12 versus 296 ± 12 in control group (p < 0.05). TBUT (sec) was 5 ± 2 versus 9 ± 2 (p < 0.05). OSDI ranged from 0 to 96 and the mean value was 18 ± 19 in the study group vs 16 ± 14 in controls (NS). No significant difference was found in corneal staining between the two groups. In POAG/OH eyes tear film osmolarity values were ≤308 in 17/50 (34%) patients and in control group were 4/20 (20%). TBUT<8 s in 41/50(82%) vs 5/20 (25%). OSDI was <12 in 50% of cases vs 55% of controls, ranging from 13 to 32 in 36% versus 30% and from 33 to 100 in 14% versus 20%; corneal staining >1 in 12% versus 10%. Tear osmolarity was significantly correlated to TBUT (r = 0.11; p = 0.05).Conclusions: The differences between OSM and TBUT are statistically significant between the two groups. OSDI score difference is not significant, but the self‐administered questionnaire has inherent limitations. Tear film osmolarimetry has the advantage of providing a quantitative, operator‐independent indication of possible ocular surface dysfunction and it may be useful in the real life practice of a glaucoma unit in identifying the most vulnerable patients who might benefit from a switch to BAK‐free preparations.