Clinical use of a new position-independent rebound tonometer

To compare intraocular pressure (IOP) measurements obtained by rebound tonometry (Icare PRO tonometer), applanation tonometry (Goldmann and Perkins tonometry), and dynamic contour tonometry in the upright and the supine positions, and to investigate the influence of axial length and central corneal thickness.

Ninety-nine right eyes of 99 patients with glaucoma or suspect for glaucoma, admitted to our department between November 2010 and January 2011 to obtain an IOP profile including supine measurements, were included in our study. IOP measurements were obtained in an upright position using an Icare PRO rebound (RTPRO), a Goldmann applanation (GAT), and a Pascal dynamic contour tonometer (DCT). In the supine position, IOP measurements were taken using the RTPRO and a Perkins hand-held applanation tonometer (PAT). The means and SDs for all tonometers were compared. Agreement between the tonometers was calculated using the Bland-Altman method.

The mean IOPs obtained in the upright position were 17.7 ± 8.0 mm Hg (RTPRO), 17.6 ± 7.8 mm Hg (GAT), and 19.9 ± 6.6 mm Hg (DCT). Correlation analysis of these data indicated a good correlation between IOP readings obtained using RTPRO and GAT (r=0.951; P<0.001), and RTPRO and DCT (r=0.897; P<0.001). Bland-Altman analysis revealed mean differences (bias) between RTPRO and GAT, and between RTPRO and DCT of 0.1 mm Hg and -1.8 mm Hg, with 95% limits of agreement of -3.6 to 3.8 mm Hg and -7.3 to 3.6 mm Hg, respectively. In the supine position, the mean IOPs were 19.2 ± 6.4 mm Hg using the RTPRO and 19.6 ± 6.2 mm Hg using the PAT.

Measurements obtained with the RTPRO, either in the upright or in the supine position, show good correlation and agreement with those provided by applanation and dynamic contour tonometry. The study was registered with the DRKS (German Clinical Trials Register; http://www.germanctr.de; DRKS00000581).