MEMS Application of Actuators and Sensors for Glaucoma Treatment

Glaucoma is an eye disease that is caused by abnormal high intraocular pressure (IOP) in the eye. If the disease becomes serious, it is recommended to use the implant device that decreases the IOP. Though conventional glaucoma implants have the capability to regulate pressure, these implants cannot maintain the IOP desired for different patients. To solve this problem, an active implant is needed that is capable of actively controlling the IOP for personal differences between patients. The active glaucoma implant consists of a valve actuator, a pressure sensor, a pressure controller, and a power supply. The focus of this work is mainly on the valve actuator and pressure sensor. For the valve actuator, different design are presented. These designs consider actuation principles, fluidic resistance elements, control methods, and energy supplies. Based on the analysis, an optimal design of the valve actuator is determined. For the implant’s pressure sensor, sensing principles, measurement methods, and the signal-to-noise ratio are considered for both piezoresistive and capacitive sensors that have been used to monitor the IOP. As an example, the design of a pressure sensor is presented that considers a bridge type sensor that uses piezoresistive materials on a membrane that is strained under pressure. An optimal design of the piezoresistive pressure sensor is determined that takes into account the signal to noise ratio of the sensor. In vitro/vivo experiments are conducted to illustrate how the performance of the fabricated valve/sensor can be obtained and verified under a similar environment for an implant in the human eye.