A portable applanation tonometer for accurate intraocular pressure measurements

Accurate intraocular pressure (IOP) measurement in a convenient way is critical for the diagnosis and treatment in glaucoma development. In this study, we present a prototype of a portable tonometer by utilizing a new applanation method. The tonometer consists of two components: a capacitive force sensor (CFSen) and a portable displacement platform (PorDP). The capacitance output of CFSen and moving distance of PorDP reflects the force exerted on the eye and the corneal applanate area respectively. A numerical model based on finite element method (FEM) has been developed to analyze the tonometer performance. In addition, the tonometer has been validated on in vitro pig eyes, from which an analytical relationship of IOP, capacitance of CFSen and moving distance of PorDP has been established. Different from the traditional applanation-based tonometer which measures the force and area at single corneal applanate state, our tonometer takes readings at several corneal applanating phases. By considering multiple corneal applanation states, the measurement error of the tonometer is in the range of −0.38 to +0.67 mmHg and the resolution is less than 1 mmHg. We believe this approach provides a technological platform to develop an advanced tonometer for accurate IOP monitoring.