IOP measurement using air-puff tonometry: Dynamic modeling of human eyeball with experimental results

IOP (Intra-Ocular Pressure) is an important factor in eye examination specifically for the diagnosis of glaucoma. The measurement of IOP has been experimentally studied for decades but the mechanism has not been fully understood yet because of the complex structure of the human eyeball. Therefore, the simulation with reasonably simple model is necessary to complement the experimental study. This paper proposes dynamic models of the human eyeball to simulate the displacement of the cornea during IOP measurement by air-puff tonometry. The parameters of proposed models are based on the experimental results presented by Kaneko et al. The deformation of the cornea is calculated by the linear system theory with parameter study. The simulation results revealed that both the stiffness and viscous damping of the eyeball affect the IOP measurement by air-puff tonometry. This finding is important, because the IOP measurement by air-puff tonometry is always compared against the IOP measured by the Goldmann applanation tonometry (GAT). However, the viscous damping does not affect the IOP measured by GAT due to low loading rate. Furthermore, the simulation results showed that the effect of the mass of the eyeball is negligible. In addition, the simulation results showed that different shapes of displacement between young and senior subjects could be explained by the decreased stiffness between the eyeball and the eye socket due to aging. Furthermore, the results verify that the difference does not affect the IOP measurement by air-puff tonometry. By comparing the simulation results and the experimental results, the effectiveness of the simulation and improvement of modeling were discussed.