The fundamental idea for measuring the intraocular pressure was proposed by the Russian physician A.N. Maklakoff as early as the end of 19th century and is still the basis for almost all the methods used in clinical practice. An improved Maklakoff’s tonometer is introduced in this paper. On the basis of this applanation tonometer, the experimental study on intraocular pressure-volume relation for the simulated eye is performed. Quantitative results and Qualitative conclusions that follow our study and may be of practical interest in finding the intraocular pressure and estimating the rigidity (stiffness) of the eyeball from the pressure–volume relationship are discussed.