Influence of corneal stiffness on measurement of intraocular pressure

Accurate measurement of intraocular pressure (IOP) is important for the clinical care of individuals at risk and those diagnosed for glaucoma. Goldmann applanation tonometery (GAT) is the gold standard for measuring IOP. However, GAT may not be accurate in some patients whose corneas are different from the population average. This project focuses on understanding how corneal stiffness may affect the accuracy of GAT. Dr. Liu and colleagues first investigated in a laboratory setting the readings of GAT on animal eyes. They found GAT read substantially lower than the experimentally-controlled true pressure in the animal eyes. They also found a significant correlation between corneal modulus (measurement of stiffness) and GAT errors. In addition, they found that GAT read much higher if they artificially increased the stiffness of the corneas. The increase in corneal stiffness correlated well with the increase in GAT readings. The team has also done the same tests in human donor eyes and observed the same significant correlation between corneal stiffness and GAT errors. These results strongly support the idea that corneal stiffness has a major impact on GAT accuracy and this should be considered clinically when abnormal corneal properties are suspected. Dr. Liu’s team has started to apply a non-invasive ultrasound method to measure corneal stiffness in people and to use that information to correct GAT measurements. They believe the results from their studies will help clinicians and researchers better understand the influence of corneal properties on the clinical measurements of IOP.