# AS-OCT and Ocular Hygrometer as Innovative Tools in Dry Eye Disease Diagnosis
## 5 Discussion  
The ocular surface system [13] is a complex morphofunctional unit made of different tissues, such as conjunctiva, cornea, lids and lacimal glands, and also a complex network of nerves [61; 62], hormones [11], immune cells [63] and metabolites [64] that interplay mainly in the tear film [12; 65], which acts as the blood flow in the other tissues. Therefore, the status of the tear film is a reflection on the ocular surface system function. Tear film analysis may be considered as a local prognostic, diagnostic and therapeutic test to assess the healthy or diseased condition of the ocular surface system and is particularly studied in the most prevalent of ocular surface diseases, such as dry eye disease [66]. Different diagnostic tests are suitable for DED diagnosis; however, their sensitivity and specificity vary significantly according to patient-specific characteristics, disease severity and other factors [14; 47]. Despite the large prevalence of DED among the population, there is no gold standard diagnostic approach to diagnose DED. Routine clinical exams poorly correlate with patient symptoms and are subject to observer bias [14; 17]. Several assessments exist to evaluate the quality and quantity of ocular surface and tear dysfunctions; however, the set of assessments that are capable of diagnosing DED with acceptable specificity and sensitivity remains unknown [17; 47]. AS-OCT is an innovative tool which allows for the specific evaluation and measurement of the quality and quantity of the tear film, but it is time-consuming, costly and requires a long learning curve since it is quite a complex procedure. The DEvice(), which quantifies the gaseous state of the tear film as the humidity variations in a closed environment, could provide specific indices for each form of imbalance and, therefore, for each form of dry eye disease. A similar technology is already used in the dermatological field for the measurement of transepidermal water loss [67]. Figure 3: (**A**) The RH increase in time considering the whole trial for patients with dry eye disease; (**B**) the RH increase in time considering the whole trial for healthy subjects; (**C**) the mean values of RH increase in time: patients with dry eye disease vs. healthy subjects. In fact, various dermatological diseases in which the skin barrier is altered are associated with an increased loss of transepidermal water. The latter can be measured indirectly, by calculating the change in the density of water vapor at the skin surface over time compared to the atmospheric humidity, using an open-chamber device, an unventilated-chamber device or a condenser-chamber device. These devices are influenced differently by the surrounding environment [68; 69]. The ocular hygrometer is an attempt to evaluate the quality and quantity of the tear film in a non-physiological context. It was developed as a sort of tear change in an artificial system. In fact, we could notice different relative humidity curves in DED patients versus the controls in our pilot study. The environmental airflow [70] would definitively affect the homeostatic equilibrium of a non-healthy tear film, but this would be subsequently related to a different relative humidity curve assessed in the device's artificial chambers. Finally, blinking, incomplete blinking and tear clearance may affect the device's measurements; therefore, further studies are required on a larger cohort of patients in order to confirm the innovative and promising early results and to improve the features of the DEvice(r). Ocular hygrometers, such as DEvice(r), represent the future scope of ocular surface diagnostic research by mixing low costs with the efficiency, accuracy, rapidity and safety (no contact) of the measurement of tear films. Conceptualization, D.G., T.M., E.S. and A.D.Z. ; methodology, E.S. and A.D.Z. ; software, A.C. and E.S. ; validation, all; formal analysis, all; investigation, all; resources, all; data curation, all; writing--original draft preparation, D.G., T.M., S.C., A.G. and C.F.