IOP measurements from Goldmann applanation tonometry (GAT) assessments aren’t all that accurate; central corneal thickness (CCT) can impact pressure readings, with IOPGAT being underestimated on thin corneas and overestimated on thick ones (1). But although several GAT correction formulas exist, how accurate are they? And how might those inaccuracies impact glaucoma care?

A Zurich-based team of researchers decided to investigate (2). “Over years working with dynamic contour tonometry (DCT) we realized that the well-known relationship between CCT and over- and underestimation of IOPGAT is not valid in all cases. The question came up of what results correction formulas provide as they calculate mainly with CCT parameters,” says corresponding author Christoph Kniestedt of Talacker Eye Center, Zurich, Switzerland. In their prospective, cross-sectional clinical trial, they measured IOP in 112 patients with glaucoma using Pascal DCT and GAT. Comparing IOPDCT with conventional (uncorrected) IOPGAT (IOPDCT-IOPGAT), they found a mean discordance of 3.3 mm Hg (p<0.001). Comparing IOPGAT that had been corrected by five separate formulas, the discordance between DCT and GAT ranged between 2.7 to 5.4 mmHg (all p<0.001).