Regardless of the device used to measure intraocular pressure (IOP), clinicians should be aware that corneal biomechanical properties such as corneal hysteresis (CH), corneal resistance factor (CRF) and central corneal thickness (CCT) can all affect the reading, a new study suggests.

An international team of researchers studied 100 patients with glaucoma or ocular hypertension using three techniques: traditional Goldmann applanation tonometry (GAT), an Icare Home self-tonometer and Reichert’s Ocular Response Analyzer.

They found the mean IOP measurements were 14.3 ±3.9mm Hg with GAT and 11.7±4.7mm Hg with the self-tonometer, a difference of -2.66 ±3.13mm Hg. When taking corneal properties into account, the researchers found a negative correlation between IOP and CH: for each 10mm Hg lower CH, IOP was 5.17mm Hg higher with the self-tonometer and 7.23mm Hg higher with GAT, “suggesting GAT was more affected by CH than Icare Home,” the study said.

In contrast, thinner CCT was significantly associated with lower IOP for both devices, with CCT affecting the self-tonometer readings to a greater degree. Once reanalyzed with CRF in the mix, CCT was no longer significant. CRF and CH remained associated with IOP using either GAT or the self-tonometer. Because the difference between GAT and self-tonometer readings was greatest with higher CCT and lower CH, the researchers advise caution when switching between tonometry modalities for long-term monitoring.

“Our results suggest IOP measurements from each of the devices tested may be underestimated in eyes with higher CH and lower CRF,” the study concludes. “This is important as the underestimation of IOP can compromise the delivery of glaucoma care, resulting in suboptimal treatment.

Brown L, Foulsham W, Pronin S, Tatham AJ. The influence of corneal biomechanical properties on intraocular pressure measurements using a rebound self-tonometer. J Glaucoma. 2018;27(6):511-8.