Changes in intraocular pressure after intraocular eye surgery-the influence of measuring technique

Abstract

Aim: To investigate the changes in intraocular pressure (IOP) before and after intraocular surgery measured with Goldmann applanation tonometry (GAT) and pascal dynamic contour tonometry (PDCT), and assessed their agreement.

Methods: Patients who underwent trans pars plana vitrectomy (TPPV) with or without cataract extraction (CE) were included. The IOP was measured in both eyes with GAT and PDCT pre- and postoperatively, where the non-operated eyes functioned as control.

Results: Preoperatively, mean IOP measurements were 16.3±6.0 mm Hg for GAT and 12.0±2.8 mm Hg for PDCT for the operated eyes. Postoperatively, the mean IOP dropped to 14.3±5.6 mm Hg for GAT (P=0.011) and rose up to 12.7±2.6 mm Hg for PDCT (P=0.257). Bland-Altman analysis showed a poor agreement between GAT and PDCT with a mean difference of 2.9 mm Hg preoperatively and 95% limits of agreement ranging from -3.2 to 9.0 mm Hg. Postoperatively, the mean difference was 1.2 mm Hg with 95% limits of agreement ranging from -8.3 to 10.7 mm Hg. There were no significant differences between the TPPV and TPPV+CE group, except when measured with PDCT postoperatively (P=0.012).

Conclusion: The IOP is reduced after surgery when measured with GAT and remained stable when measured with PDCT. However, the agreement between GAT and PDCT is poor. Although PDCT may be a more accurate predictor of the true IOP, it seems less suitable for daily use in the clinical practice.

Keywords: glaucoma; intraocular pressure; intraocular surgery; trans pars plana vitrectomy.

Figure 1. Flow chart of included eyes.

Figure 2. Bland-Altman plot of the difference in preoperative (A) and postoperative (C) intraocular pressure (IOP) between Goldmann applanation tonometry (GAT) and Pascal dynamic contour tonometry (PDCT) plotted against the average IOP, with corresponding scatterplot of the preoperative (B) and postoperative (D) average of GAT versus the average of the PDCT

In the Bland-Altman plot the solid line represents the mean difference and the dashed lines represent the 95% limits of agreement. The quality of the PDCT measurements are shown as circles (Q1), squares (Q2), and triangles (Q3). In the scatterplot the solid line represents the line y=x. The dashed line represents the regression line.