Mathematical models of intraocular pressure measurements and ocular rigidity

The term ocular rigidity is widely used in ophthalmology. Generally it is assumed as a measurable physical parameter related to biomechanical properties of the whole eye globe. Formulas for clinical tonometry and tonography methods include the concept of ocular rigidity. Unfortunately ocular rigidity represents an elusive concept that means many things to many people. First of all, there is no consensual view on ocular rigidity in ophthalmology. The most of the formulas for ocular rigidity are based on discrete or continuous tonometric measurements in living or enucleated human eyes. Surprisingly ocular rigidity is measured in different units and has a different meaning by different authors. Finally, there is no clear consent between biomechanical engineers and ophthalmologists on the concept of ocular rigidity. In biomechanics parameters for the elasticity and viscoelasticity are accepted, which represent mechanical properties of a tissue an can consider its morphology. These are for example: Young’s moduli of the sclera, Poisson’s ratios of the cornea etc. Ophthalmological concepts on ocular rigidity are based on the consideration, that biomechanical properties of the corneoscleral shell are involved in the pressure-volume relationship of the eye globe. Ocular rigidity defined in such a way climes to describe the total response of the eye without detailed considerations on its morphologic and material properties. In the proposed review several formulations of ocular rigidity are analysed and classified. It is attempted to link these conceptions with each other.