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The influence of corneal geometrical and biomechanical properties on tonometry readings in keratoconic eyes

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Abstract

Purpose

To identify the effect of corneal geometrical and biomechanical parameters on the intraocular pressure (IOP) measurements obtained by Goldmann Applanation Tonometer (GAT), non-contact tonometer, iCare Pro Rebound Tonometer (IRT), Tonopen and Ocular Response Analyzer (ORA, Goldmann-correlated IOP: IOPg, corneal compensated IOP: IOPcc).

Methods

We prospectively recruited patients with a tomographically confirmed diagnosis of keratoconus. IOP measurements were performed in the following order: non-contact tonometry, ORA, IRT, GAT and Tonopen. The means of the three IOP measurements were used for the analysis. Correlation analyses were performed to assess the association between tonometer readings and the corneal geometrical and biomechanical parameters including ORA waveform parameters. Tonometer variability was assessed using a stepwise linear regression analysis.

Results

Fifty-one patients with keratoconus (27 females, mean age 30.8 ± 8.7 years) were evaluated. The highest mean IOP was measured by IOPcc (14.6 ± 2.3 mmHg) followed by IRT IOP (13.0 ± 3.2 mmHg), Tonopen IOP 12.0 ± 2.6 mmHg), GAT IOP (11.7 ± 3.1 mmHg), NCT IOP (10.2 ± 3.2 mmHg) and IOPg (10.2 ± 3.6 mmHg). NCT and IOPg were affected from all corneal parameters including thickness, curvature and biomechanical parameters. While GAT and IRT had significant correlations with corneal resistance factor (CRF) and corneal hysteresis, IOPcc only had a significant correlation with CRF. None of the corneal factors had any statistically significant correlation with Tonopen. CRF predicted tonometer measurement variability in 7 of the 15 inter-device variability assessments.

Conclusion

Tonopen was the least affected from the corneal parameters followed by IOPcc and GAT. CRF was a strong determinant of tonometer variability.

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Acknowledgements

We thank Drs. Onur Özalp and Serdar İlgüy for their help in IOP measurements.

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Authors and Affiliations

  1. Department of Ophthalmology, Eskişehir Osmangazi University Medical School, Eskişehir, Turkey

    Mustafa Değer Bilgeç, Eray Atalay, Ömer Sözer, Hüseyin Gürsoy & Nilgün Yıldırım

  2. Department of Biostatistics, Eskişehir Osmangazi University Medical School, Eskişehir, Turkey

    Muzaffer Bilgin

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  1. Mustafa Değer Bilgeç
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  2. Eray Atalay
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Correspondence to Eray Atalay.

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All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. This cross-sectional study was approved by the Clinical Research Ethical Board of the Eskisehir Osmangazi University and was conducted in adherence to the tenets of the Declaration of Helsinki.

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Bilgeç, M.D., Atalay, E., Sözer, Ö. et al. The influence of corneal geometrical and biomechanical properties on tonometry readings in keratoconic eyes. Int Ophthalmol 40, 849–857 (2020). https://doi.org/10.1007/s10792-019-01248-9

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