0
Research Papers

Assessment of the Ocular Response Analyzer as a Tool for Intraocular Pressure Measurement

[+] Author and Article Information
Ahmed Elsheikh1

Division of Civil Engineering, University of Dundee, Dundee DD1 4HN, UKa.i.h.elsheikh@dundee.ac.uk

Daad Alhasso

Division of Civil Engineering, University of Dundee, Dundee DD1 4HN, UKd.alhasso@dundee.ac.uk

Aachal Kotecha

NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London EC1V 9EL, UK; Department of Optometry and Visual Science, City University, London EC1V 0HB, UK

David Garway-Heath

NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London EC1V 9EL, UK; GB Bietti Foundation for Research in Ophthalmology—IRCCS, Rome, Italy

1

Corresponding author.

J Biomech Eng 131(8), 081010 (Jul 06, 2009) (9 pages) doi:10.1115/1.3148462 History: Received August 08, 2008; Revised November 11, 2008; Published July 06, 2009

The ocular response analyzer (ORA) is a new indentation tonometer that subjects the cornea to an increasing then decreasing air pulse, and uses the corresponding two applanation pressures P1 and P2 to estimate the intraocular pressure (IOP). The present study aims to improve the accuracy of IOP estimation through representative numerical simulation of the ORA procedure. A parametric study has been carried out to consider the effect of corneal thickness, curvature, age, and true IOP on the P1 and P2 measurements. Based on the obtained database of input and output parameters, an equation has been suggested relating the P1 and P2 measurements to the value of IOP. The equation is intended to make IOP estimates independent of corneal stiffness, which varies with size and age. The equation has been tested against a clinical data set obtained at Moorfields Eye Hospital involving 144 subjects, and found to produce IOP estimates that are less dependent on corneal size and age than published equations.

FIGURES IN THIS ARTICLE
<>
Copyright © 2009 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Figure 1

Overall views of a numerical model with 6 layers and 20 rings; (a) view from the anterior side, (b) view from the posterior side showing also model layers, and (c) cross-sectional view showing variable corneal thickness from minimum at center to maximum at periphery

Grahic Jump Location
Figure 2

Stress distribution diagrams for a cornea with CCT=520 mm, R=7.8 mm, age=57 years, and IOP=15 mm Hg, during the progress of the ORA procedure showing areas of loading and unloading; (a) typical material loading-unloading behavior, (b) key showing stress values in MPa, (c) cross-sectional view at start, (d) stresses after applying the intraocular pressure on the model’s posterior side, (e) stresses at first applanation, (f) stresses under Pmax, beyond which the air pressure starts to decrease; (g) stresses at second applanation; and (h) stresses after complete removal of air pressure

Grahic Jump Location
Figure 3

Air pressure distribution as applied by the ORA on the cornea’s anterior surface

Grahic Jump Location
Figure 4

The relationships between ΔP1 and ΔP2 as obtained from numerical simulations for corneas aged between: (a) 50 and 64 years, (b) 65 and 79 years, and (c) 80 and 95 years. The solid lines represent the results of linear regression analysis of clinical data for subjects aged 50–64.9 years and 65–79.9 years.

Grahic Jump Location
Figure 5

The relationships between ΔP1 and Δtrue IOP (IOPT) as obtained from numerical simulations for corneas with age between: (a) 50 and 64 years, (b) 65 and 79 years, and (c) 80 and 95 years. The solid lines represent the results of linear regression analysis of clinical data for subjects aged 50–64.9 years and 65–79.9 years.

Grahic Jump Location
Figure 6

Effect of the value of parameter k on the slope of association between the corneal factor, CF, and (a) CCT and (b) age

Grahic Jump Location
Figure 7

Strength of association between the corneal factor, CF, and IOP for a range of k between 0 and 2

Grahic Jump Location
Figure 8

Assessment of the strength of association between the corneal factor, CF, and (a) IOP, (b) CCT, and (c) R, for different values of k

Grahic Jump Location
Figure 9

Variation of ORA IOP and GAT IOP with the CCT, as obtained from the analysis of a clinical data set while (a) excluding subjects outside the 50–95 year age range, and (b) including all subjects

Grahic Jump Location
Figure 10

Variation of ORA IOP and GAT IOP with age as obtained from the analysis of a clinical data set while (a) excluding subjects outside the 50–95 year age range, and (b) including all subjects

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In