Address of Corresponding Author

Ophthalmic Res 2006;38:49-55 (DOI: 10.1159/000089762)

  Key Words

• Goldmann applanation tonometry
• Intraocular pressure
• Slit-scan tomography
• Pachymetry
• Astigmatism

  Abstract

Background: The aim of this study was to evaluate the impact of various sources of error in Goldmann applanation tonometry (GAT). Objectives: We evaluated the effect of corneal thickness, curvature, astigmatism and direction of gaze as sources of error in GAT. Methods: Orbscan-II^® (Bausch & Lomb, Inc., Rochester, N.Y., USA) examinations were made on 30 healthy subjects and 9 keratoconus patients, and the intraocular pressure (IOP) was measured with GAT centrally, temporally and inferiorly, with the tonometer prism set horizontally and vertically. Orbscan-II images from 50 younger subjects and 49 older subjects were analysed retrospectively. Results: IOP was lower on nasal gaze (p = 0.009) but higher on upward gaze (p < 0.001) compared with forward gaze. IOP and the corneal thickness were independently correlated (R² = 0.04; p = 0.003), as were the difference in astigmatic vector in the horizontal and vertical meridians and the difference in IOP measured with a horizontal and vertical prism (R² = 0.17; p < 0.001). No correlation between IOP and corneal curvature was found. In the keratoconus patients, IOPs were generally low, with large astigmatic differences. Conclusions: Corneal thickness, astigmatism and direction of gaze are clinically important sources of error in GAT. IOP should preferably be measured with the prism both horizontally and vertically. If only one direction is chosen, a vertical prism is less sensitive to different directions of gaze. Direction of gaze should be carefully monitored, especially in an irregular cornea.

Copyright © 2006 S. Karger AG, Basel

  Author Contacts

Anders Behndig, MD, PhD
Department of Clinical Sciences/Ophthalmology
Umeå University Hospital
SE-901 85 Umeå (Sweden)
Tel. +46 90 785 37 31, Fax +46 90 13 34 99, E-Mail anders.behndig@ophthal.umu.se

  Article Information

The authors have no financial interest in any product mentioned in this paper.

Received: June 6, 2005
Accepted after revision: August 15, 2005
Published online: November 16, 2005
Number of Print Pages : 7
Number of Figures : 5, Number of Tables : 4, Number of References : 23