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National Glaucoma Research
Completed Award

Photo Pending

Jun Liu, Ph.D.

The Ohio State University
Columbus, OH

Title: Corneal stiffness and tonometric measurements of IOP
Non-Technical Title: Influence of corneal stiffness on measurement of intraocular pressure

Acknowledgements: Recipient of the Thomas R. Lee award for National Glaucoma Research
Duration: April 1, 2010 - September 30, 2012
Award Type: Standard
Award Amount: $100,000

Summary:

Accurate measurement of intraocular pressure is important for glaucoma management. The clinical standard, Goldmann applanation tonometry is known to be affected by corneal thickness and potentially other corneal factors. This study investigates how corneal stiffness may affect the accuracy of Goldmann tonometric measurement of intraocular pressure.

Details:

The intraocular pressure (IOP) is an important parameter that physicians measure in order to make diagnostic and treatment decisions for glaucoma suspects and patients. Goldmann applanation tonometry is accepted as the clinical standard for measuring IOP. Nevertheless, it is known that this device may not be accurate for some subjects whose corneal properties are different from the average of the population. We have theoretically analyzed the measurement procedure and found that potentially significant errors could be present in the measurements due to the variance of corneal properties. For example, thick and stiff corneas may lead to an overestimation of IOP while thin and soft corneas may lead to underestimation. This application will study how the stiffness of the cornea could affect the accuracy of Goldmann tonometry. Our laboratory has developed a non-invasive method that allows us to measure corneal stiffness in humans in a safe and convenient way. With this technique and other experimental tools we have assembled, we are studying: 1. the influence of corneal stiffness on the accuracy of IOP measurements in an experimental porcine (pig) eye model, 2. the influence of corneal stiffness on the accuracy of IOP measurement in human donor eyes, and 3. the effect of corneal stiffness on clinical IOP measurement. These studies will help us better understand the impact of corneal properties on the measurement of IOP, and lead to more accurate methods for monitoring IOP during the course of glaucoma diagnosis and treatment.

Publications:

J Tang, X Pan, PA Weber, and J Liu, Corneal modulus and IOP measurements in canine eyes using Goldmann applanation tonometry and Tonopen, Investigative Ophthalmology and Visual Science, 52(11): 7866-7871, 2011 PubMed Icon Google Scholar Icon

J Tang, X Pan, PA Weber, and J Liu, Effect of corneal stiffening on Goldmann Applanation Tonometry and Tonopen measurements in canine eyes, Investigative Ophthalmology and Visual Science 53(3): 1397- 1405, 2012. PubMed Icon Google Scholar Icon

J Tang, X Pan, PA Weber, and J Liu, Corneal modulus and IOP measurements in canine eyes using Goldmann applanation tonometry and Tonopen, Investigative Ophthalmology and Visual Science, 52(11): 7866-7871, 2011

J Tang, X Pan, PA Weber, and J Liu, Effect of corneal stiffening on Goldmann Applanation Tonometry and Tonopen measurements in canine eyes, Investigative Ophthalmology and Visual Science 53(3): 1397- 1405, 2012.

Progress Updates:

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.

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