Humidity Sensor to Support Dry Eye Diagnosis Based on Polymeric PVDF Transfer Membrane

A system based on polyvinylidene fluoride (PVDF) polymeric transfer membrane was developed as an ocular humidity sensor to support the diagnosis of dry eye. An experimental arrangement was implemented where the devices utilized to observe the behavior of PVDF transfer membrane as a humidity sensor were installed, on the contour of an artificial eye model, held with a contact lens, formed by an elastic balloon that is exposed to triple distilled water and artificial tears, on the order of 0– $40~\mu \text{L}$ , with a resolution of $10~\mu \text{L}$ . Measures were taken simulating four constant intraocular pressures (IOPs), i.e., 10, 15, 20, and 25 mmHg. The pressure exerted on both elastic artificial eyes is done simultaneously through communicating vessels. Similarly, the IOP of the artificial eye was recorded using a Schiötz tonometer and an MPX2010 GP sensor, in the range of 10–25 mmHg. The response of the PVDF transfer membrane showed a proportional relationship between capacitance changes and humidity (lack of humidity or dryness) in the artificial eye model. Capacitance measurements were made at room temperature at 25 °C, using an HM818-Rohde and Schwarz bridge $\textit {LCR}$ meter. Finally, capacitance response was converted to frequency with an astable oscillator to optimize signal processing and visualization. These polymeric PVDF transfer membranes sensors are a hydrophobic material, which prevents the storage of water molecules in the sensing material and allows liquid or artificial tears to flow freely. In summary, polymeric PVDF transfer membranes exhibit suitable properties as a dry eye humidity sensor at realistic IOPs.