Tonometry agreement and corneal biomechanical features in normal, glaucomatous and keratoconic eyes

Abstract

Intraocular pressure measurement is a routine clinical examination performed in ophthalmic practice. It is vital in clinical monitoring, diagnosis and management of certain eye diseases. There are many types of tonometers currently available to measure the intraocular pressure (IOP). These tonometers employ different technologies compared to the standard Goldman applanation tonometer (GAT). Studies often report inter-tonometry agreement and bias of new tonometers against GAT. However, only a minority have studied the proportionate bias and factors that influence the inter-tonometry bias of a new tonometer. The inter-tonometry agreement is vulnerable to the influence of corneal physical and mechanical properties. The information on reliability and agreement between different tonometers is very important in the management of ocular diseases. The aim of this thesis was to examine the inter-tonometry agreement between five different tonometers. The influence on IOP of demographic and ocular factors was investigated. This thesis investigates the biomechanical characteristics of the cornea of normal, glaucomatous and keratoconus subjects and the factors that influence biomechanical parameters. The tonometers employed were found to have a good agreement with GAT but the tonometry values were not interchangeable. The bias of each tonometer was influenced differently by central corneal thickness (CCT), specific corneal biomechanical parameters and age. Clinicians should be cautious when examining glaucoma and keratoconus patients with different tonometers, as most demonstrate significant proportionate bias. The corneal biomechanical parameters in subjects with different ocular diagnoses revealed variable significance and was influenced by age, CCT and corneal curvature. Future research to identify unique corneal parameters in different ocular conditions may be of importance especially in screening and diagnosis.