Clinically relevant artefactual intraocular pressure lowering resulting from corneal biomechanical changes under latanoprost treatment: data from the UKGTS.

Abstract

Purpose : There is controversy regarding whether prostaglandin analogues induce a change in corneal biomechanics. It has been hypothesised that their action on metalloproteinases could modify corneal properties and alter intraocular pressure (IOP) measurements. This was tested in the United Kingdom Glaucoma Treatment Study (UKGTS) IOP measurements with different tonometers.

Methods : Among the 516 UKGTS participants with newly diagnosed open-angle glaucoma, 483 (240 placebo, 243 latanoprost) with complete data of Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT) were included for analysis. Participants were randomized to Latanoprost 0.005% (treatment) or placebo (control) once a day, to both eyes. Data from the first 6 visits (13-month follow-up) were analysed. Linear regression between GAT or DCT and CCT in 230 patients from the placebo group confirmed that DCT IOP is much less affected by corneal biomechanics and supported the use in our analysis as the IOP measurement that better represents the true IOP. We used linear regression comparing the relation between GAT and DCT in placebo and latanoprost groups to test the hypothesis that, if latanoprost affects corneal biomechanics, the regression lines would show similar slopes but different intercepts. A multivariable regression was constructed to predict GAT IOP from CCT, DCT, and treatment group.

Results : GAT IOP, but not DCT IOP, was significantly associated with CCT (GAT: R²=0.02, p=0.028, DCT: R²=0.003, P=0.49). The linear regression comparing GAT with DCT showed a positive association in both groups with very similar slopes, but a difference of 1.35 in intercepts (y=1.87+0.89x, R²=0.69, P<0.001 in the placebo group vs y=0.52+0.88x, R²=0.69, P<0.001 in the latanoprost group). The multivariable regression analysis showed that GAT IOP is explained by DCT IOP, CCT and randomization to latanoprost (R² 0.70), with a highly statistically significant additional 1.15mmHg difference between the tonometers (p=0.0001) [latanoprost lower].

Conclusions : Latanoprost treatment is associated with an additional 1.15mmHg difference between GAT and DCT IOP compared with placebo. Given that DCT is less affected by corneal biomechanics, this suggests a latanoprost-induced biomechanical change. This should be considered when the efficacy of different IOP-lowering drops is compared using GAT.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.