Correlation between osmolarity measurements using the TearLab? and I-Pen? systems in subjects with a high body mass index

Background. Osmolarity is used to detect symptoms of dry eye disease (DED) and can be measured using TearLab (TM) and I-Pen (R) systems. Objectives. To investigate the correlation between osmolarity measurements using the TearLab (TM) and I-Pen (R) systems in subjects with a high body mass index (BMI). Materials and methods. Thirty male subjects with a high BMI (27-48 kg/m(2); 23.3 +/- 2.1 years old) participated in this study. The control group consisting of 30 healthy males (24.9 kg/m(2); 22.9 +/- 2.1 years old) was also enrolled. Osmolarity measurements were recorded from the right eye using the TearLab (TM) and I-Pen (R) systems, and interviews were conducted to determine ocular surface disease index (OSDI) scores. Results. The OSDI (p = 0.042), TearLab (TM) (p < 0.001) and I-Pen (R) (p < 0.001) scores were significantly higher in the study group than in the control group. In the study group, OSDI scores ranged from 2 to 16 (median 8.0, interquartile range (IQR) 6.8), while it was from 0 to 10 (median 6.3, IQR 4.1) in the control group. The TearLab (TM) osmolarity scores were in the range of 278-309 mOsm/L in the study group, whereas the I-Pen (R) osmolarity measurements were in the range of 294-336 mOsm/L in the study group, compared with 263-304 mOsm/L and 278-317 mOsm/L in the control group, respectively. In the study group, there was a strong correlation between the TearLab (TM) and I-Pen (R) osmolarity scores (r = 0.934; p = 0.001). In addition, strong correlations were found between the BMI and both TearLabT (r = 0.736; p = 0.001) and I-Pen (R) (r = 0.707; p = 0.001) scores, as well as between the OSDI scores and both TearLab (TM) (r = 0.731; p = 0.001) and I-Pen (R) measurements (r = 0.666; p = 0.001). Conclusions. Osmolarity measurements using the I- Pen (R) system were significantly higher than those recorded using the TearLab (TM) system in subjects with a high BMI. The I-Pen (R) measurements showed large variations in osmolarity scores and were highly unreliable in correctly identifying normal eyes compared to the TearLab (TM) system. Also, a strong correlation was found between the osmolarity scores obtained from the TearLab (TM) and I-Pen (R) systems.