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Evaluation of Goldmann Applanation Tonometry Using a Nonlinear Finite Element Ocular Model

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Abstract

Goldmann applanation tonometry (GAT) is the internationally accepted standard for intra-ocular pressure (IOP) measurement, which is important for the diagnosis of glaucoma. The technique does not consider the effect of the natural variation in the corneal thickness, curvature and material properties. As these parameters affect the structural resistance of the cornea, their variation is expected to lead to inaccuracies in IOP determination. Numerical Analysis based on the finite element method has been used to simulate the loading conditions experienced in GAT and hence assess the effect of variation in corneal parameters on GAT IOP measurements. The analysis is highly nonlinear and considers the hyper-elastic J-shaped stress–strain properties of corneal tissue observed in laboratory tests. The results reveal a clear association between both the corneal thickness and material properties, and the measured IOP. Corneal curvature has a considerably lower effect. Similar trends have been found from analysis of clinical data involving 532 patients referred to the Glaucoma Unit at Moorfields Hospital, and from earlier mathematical analyses. Nonlinear modelling is shown to trace the behaviour of the cornea under both IOP and tonometric pressure, and to be able to provide additional, and potentially useful, information on the distribution of stress, strain, contact pressure and gap closure.

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Abbreviations

CCT:

central corneal thickness

GAT:

Goldmann applanation tonometry

IOP:

intra-ocular pressure

IOPG:

intra-ocular pressure as measured by GAT

IOPT:

true intra-ocular pressure

PCT:

peripheral corneal thickness

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Authors and Affiliations

  1. Division of Civil Engineering, Faculty of Engineering, University of Dundee, Dundee, DD1 4HN, UK

    Ahmed Elsheikh, Defu Wang & Michael Brown

  2. Glaucoma Research Unit, Moorfields Eye Hospital, London, EC1V 2PD, UK

    Aachal Kotecha & David Garway-Heath

  3. Department of Optometry and Visual Science, City University, London, UK

    Aachal Kotecha & David Garway-Heath

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  1. Ahmed Elsheikh
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  2. Defu Wang
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  3. Aachal Kotecha
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  4. Michael Brown
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  5. David Garway-Heath
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Correspondence to Ahmed Elsheikh.

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Elsheikh, A., Wang, D., Kotecha, A. et al. Evaluation of Goldmann Applanation Tonometry Using a Nonlinear Finite Element Ocular Model. Ann Biomed Eng 34, 1628–1640 (2006). https://doi.org/10.1007/s10439-006-9191-8

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  • DOI: https://doi.org/10.1007/s10439-006-9191-8

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