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Optom Vis Sci. 2008 Jun;85(6):445-50. doi: 10.1097/OPX.0b013e3181783a70.

Young's modulus in normal corneas and the effect on applanation tonometry.

Author information

1
School of Optometry and Vision Sciences, University of New South Wales, Sydney, New South Wales, Australia. HamiltonKE1@cardiff.ac.uk

Abstract

OBJECTIVES:

To determine the statistically normal range of corneal Young's modulus in young healthy eyes in vivo, and to establish if this variation has a clinically significant influence on intraocular pressure (IOP) measurement using applanation tonometry.

METHODS:

Central corneal curvature, central corneal thickness (CCT), and applanation IOP (Goldmann tonometer) were measured using standard clinical techniques in one eye of 100 normal human subjects (22.0 +/- 2.9 years) in vivo. The Orssengo-Pye algorithm was used to calculate the corneal Young's modulus of these experimental subjects, and to produce a theoretical model of potential errors in Goldmann applanation tonometry estimates of IOP due to variations of Young's modulus and CCT.

RESULTS:

Corneal Young's modulus was 0.29 +/- 0.06 MPa [95% confidence interval (CI) 0.17 to 0.40 MPa]. According to the Orssengo-Pye model, the relationship between Young's modulus and the error in applanation IOP is linear; the slope was 23 mm Hg per MPa. An increase from the minimum to the maximum value of the calculated limits of agreement (95% CI) of Young's modulus caused a variation in applanation IOP of 5.35 mm Hg. The anticipated error at the extremes of the limits of agreement (95% CI) of CCT was similar at 4.67 mm Hg.

CONCLUSION:

Physiological variations in corneal Young's modulus may cause clinically significant errors in Goldmann applanation tonometry estimates of IOP.

PMID:
18521022
DOI:
10.1097/OPX.0b013e3181783a70
[Indexed for MEDLINE]

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