# AS-OCT and Ocular Hygrometer as Innovative Tools in Dry Eye Disease Diagnosis
## 4 Innovative Device  
Nowadays, clinicians are still missing a single, non-invasive and fast test to easily diagnose DED in its alternative forms. Several innovative devices have been developed to reach this unmet need in the DED field. In particular, several studies have focused on the development of ocular hygrometers, such as DEvice(r) (AI, Rome, Italy), which allow the assessment of the DED diagnosis as well as its alternative subtype, evaporative or hypo-secretive, by a single measurement. DEvice(r) is a low-cost prototype (Figure 1a,b) able to rapidly detect the entity of production, the clearance and the stability, as well as the severity of the evaporation of the tear film, and then drives the subsequent treatment by the use of easy algorithms. This diagnostic tool is also effective in the local nebulization of drugs, leading to an alternative future therapeutic use of the instrument. Figure 1: \(Cont.\)  
The two units are directly connected in a complete diagnostic-therapeutic tool for the management of the ocular surface but are also designed and built to be used independently. When focusing on the balance between the liquid and gaseous state of the tear film, quantifying the latter by the level of humidity and its variations in a closed environment would  
Figure 1: (**a**) DEvice® ocular hygrometer. (**b**) A schematic design of the diagnostic tool system. The figure shows a side and rear view of the schematic representation of a mono sensor diagnostic prototype with: an eyepiece cup (10); the sensor (20) placed inside it; a processing board (30) equipped with processor (31), memory (34) and wireless connection device (32); the optional connection cable (33); a digital screen (40) with buttons (41); and a rechargeable power supply battery (50) placed in the handle. provide specific indices for each form of imbalance and, therefore, for each form of dry eye disease. Then, the diagnostic part of the device acts by evaluating the evaporation of the tear film from the ocular surface by means of measurements made at a variable rate, which can be adjusted by the operator. The instrument is based on the measurement of the relative humidity (RH) variation in a closed microenvironment around the ocular surface (Figure 2). RH can be expressed as RH = \(\rho\omega/\rho\)s \(\times\) 100%, where \(\rho\omega\) is the water vapor density and \(\rho\)s is the saturated water vapor density. Therefore, the advantage of using a sensor that can distinguish the RH differences between those affected by the various forms of dry eye disease/ocular surface pathologies and the normal population through its measurements is evident. The sensor measures the RH value at a given temperature and is placed inside a cup that is to be placed in front of the ocular surface, which is placed by the operator on the orbital margins. This cup and the overall ocular surface system constitute the closed environment in which the measurements are performed. From the data obtained, the progression curves of RH, corrected for temperature, can be constructed. Furthermore, the instrument allows the defining of the time t0 and time t1 at which to evaluate the RH value and to measure the time necessary to reach a given RH value. This constitutes a new frontier in the diagnostic analysis of dry eye disease and in the future, other functions and indices may be defined according to its particularly high versatility and its non-contact/invasive measurement. The non-contact system eliminates the bias generated by the direct interaction with the ocular surface of our actual tests. The measurements obtained constitute \"basal\" values that are integrated with measurements taken as a result of various types of stimuli, such as puffs of air, temperature changes in the microenvironment around the ocular surface, light stimuli, etc. Furthermore, in designing this diagnostic unit, the importance of the patient's subjective value of discomfort was taken into account.