Numerical Study of Cornea Applanation by Using a Portable Force-Displacement Sensor for Intraocular Pressure Measurements

摘要

Intraocular pressure (IOP) is considered as a critical sign for glaucoma diagnosis. Tonometry, such as Goldmann applanation tonometry, Tono-Pen and noncontact tonometry, are widely used in clinical practices for IOP evaluations. However, limitations of the tonometry, such as high cost, operating complexity, and lack of feasibility are major concerns in a busy clinic. In this paper, we propose a facile method for IOP monitoring by utilizing a simple constructed force/displacement-hybrid sensor. The device is constructed by a capacitive force sensor mounted on handheld linear stage, which is able to record the force and travel distance simultaneously. A numerical study based on the finite element method (FEM) is used to evaluate the performance of the sensor for the IOP detections. In particular, a numerical corneal-sensor model is built by the FEM, in which the sensor is placed on the apex of the corneal structure. As the sensor presses against the cornea, the physical parameters, such as the contact pressure, the contact area between the sensor and the cornea, the travel displacement of the sensor are recorded. Importantly, to improve the modeling accuracy, we use a dynamic Young's modulus in the cornea model, considering the multi-layered structure of the human cornea whose Young's modulus varies as the IOP changes. Our sensor exhibits a highly linear relationship between the contact pressure and the travel displacement in the progress of cornea applanation, from which the IOP can be simply derived. A minimal pressure of lmmHg can be sensitively detected by our sensor, which is highly desired in clinical trials.