Biomechanical properties of the cornea and tonometry measurements

Abstract

To study peculiarities of intraocular pressure (IOP) measurement by different methods in patients with changes in corneal biomechanical properties. The study enrolled 154 patients (290 eyes) divided into 3 groups according to the condition of their corneas in terms of biomechanical properties. Group I consisted of 84 patients (168 eyes) with conditionally 'normal' cornea and corneal thickness ranging from 470 to 660 μm. Group II included 44 patients (70 eyes) with keratokonus. Group III consisted of 26 patients (52 eyes) after LASIK. IOP pressure was measured in each patient by pneumotonometry, Maklakov tonometry, and dynamic bidirectional pneumo-applanation of the cornea. Biomechanical properties were evaluated with dynamic pneumo-impression method. The study revealed that in patients of groups I and III, corneal biomechanics affected indices of corneal compensated IOP and Maklakov's IOP to a lesser extent, as opposed to measurements of Goldman tonometry and pneumotonometry. In group II, Maklakov's tonometry had less IOP measurement inaccuracies in comparison to other evaluated methods due to larger applanation surface. Changes in biomechanical properties of the cornea can complicate interpretation of the results of different methods of IOP measurement. Accurate determination of IOP requires consideration of biomechanical properties of the cornea, as well as anamnesis data on past corneal diseases or keratorefractive surgeries.