Design of an Optical Pressure Measurement System for Intraocular Pressure Monitoring

This paper studies the design and application of an interferometric sensor system intended for measuring intraocular pressure. The system consists of a hermetically sealed, biocompatible, wireless, and powerless interferometric pressure sensor and a portable handheld reader. The interferometric pressure sensor consists of a 200 nm silicon nitride diaphragm, a <inline-formula> <tex-math notation="LaTeX">$10~\mu \text{m}$ </tex-math></inline-formula> SU-8 spacer, and a <inline-formula> <tex-math notation="LaTeX">$200~\mu \text{m}$ </tex-math></inline-formula> glass substrate. As monochromatic light is directed towards the sensor cavity, interference fringes between the silicon nitride diaphragm and the glass substrate form as a function of the applied pressure. In-vitro measurements show pressure in the range of 0–60 mmHg can be determined reliably with an accuracy of ±0.3 mmHg, while ex-vivo experiments using rabbit cornea showed an accuracy of ±0.6 mmHg. The resolution of the sensor is 0.2 mmHg. These results demonstrate the ability of the system to measure small changes in pressure, including intraocular pressure of glaucoma patients.