Recent research continues to clarify the ways in which measures of intraocular pressure (IOP) are affected by corneal properties such as central corneal thickness (CCT) and corneal hysteresis (CH). One study found thinner CCT was significantly associated with lower IOP; for each 10mm Hg lower CH, IOP was 7.23mm Hg higher with traditional Goldmann applanation tonometry (GAT).1 So what’s a clinician to do? Update your tools, according to researchers in Arizona.

The team found a modified surface GAT prism provided more accurate IOP readings when patients had particularly thick or thin corneas. They measured IOP in 243 eyes with five traditional Goldmann prisms and five modified prisms. With six investigators measuring each eye twice, the study included a total of 1,936 IOP readings. After crunching the numbers, they found the difference in IOP measurements between the standard and modified prisms correlated well to CCT, especially in corneas less than 500µm and more than >600 µm). CH significantly correlated to the difference in prism measurements as well.

“A simple modified replacement prism for any Goldmann-type tonometer may significantly improve IOP measurement accuracy by minimizing corneal biomechanical errors associated with CCT and CH,” the study concludes. 

McCafferty SJ, Tetrault K, McColgin A, et al. Modified Goldmann prism intraocular pressure measurement accuracy and correlation to corneal biomechanical metrics: multicentre randomised clinical trial. Br J Ophthalmol. February 22, 2019. [Epub ahead of print].