The measurement of intraocular pressure (IOP) by Goldmann applanation tonometry (GAT) is based on assumptions about corneal parameters. To correct for variations in corneal curvature and thickness, a number of equations have been proposed. This study evaluates the in vivo accuracy of these equations from individuals with primary open-angle glaucoma and compared them with measurements taken using the Pascal dynamic contour tonometer (DCT), which makes no assumptions about the corneal geometry or biomechanics.
The study included 108 participants with primary open-angle glaucoma (47 male and 61 female) with an age range of 39 to 81 years. Participants were recruited from the Glaucoma Clinic at Wroclaw Medical University. A full ophthalmologic examination was conducted on all participants. Participants were divided into 3 groups depending on IOP as measured by GAT. Six formulae were applied and the results were compared with measurements taken with DCT.
To determine as to which formula provides the closest value to IOP measured with DCT.
For IOP values ≤29 mm Hg, 2 of the formulae showed the smallest and comparable mean differences and SDs between corrected IOP values obtained with GAT and those measured with DCT. For IOP≥30 mm Hg, the formula derived from the model of corneal applanation that takes into account corneal buckling showed the closest agreement with measurements taken using DCT.
Correction formulae provide widely varying results and their appropriateness can depend on the IOP values.
*Department of Optics and Photonics
†Deformable Body Mechanics Faculty Unit, Wroclaw University of Technology, Smoluchowskiego, Wroclaw, Poland
‡School of Life Sciences, Faculty of Science, Engineering and Computing, Kingston University London, UK
Supported in part by the grant from the Polish National Centre for Research and Development, number NR13-0012-10.
Disclosure: The authors declare no conflict of interest.
Reprints: Magdalena Asejczyk-Widlicka, PhD, Department of Optics and Photonics, Wrocław University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wrocław, Poland (e-mail: firstname.lastname@example.org).
Received July 24, 2015
Accepted October 25, 2016