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M. Neuburger, S. Lautebach, J. Jordan; A Comparison of the Ocular Response Analyzer With Goldmann Applanation Tonometry and Dynamic Contour Tonometry Among Glaucoma Patients: An Analysis of Measurement Agreement and Possible Impact of Corneal Biomechanical Properties. Invest. Ophthalmol. Vis. Sci. 2008;49(13):702. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The Ocular Response Analyzer (ORA) is a new device for measuring intraocular pressure (IOP), taking into account the biomechanical properties of the cornea by also measuring the corneal hysteresis (CH) and creating a corneal resistance factor (CRF). In this study we compared the ORA to Dynamic Contour Tonometry (DCT) and Goldmann Applanation Tonometry (GAT) in glaucoma patients to investigate the specific influence of corneal biomechanical properties on intraocular pressure measurement.
Measurement was taken in 166 eyes of 83 glaucoma patients with different glaucoma diseases (primary open angle glaucoma (POAG) n = 35, normal tension glaucoma (NTG) n = 15, ocular hypertension (OHT) n = 16, pseudoexfoliation glaucoma (PEXG) n = 17). Central corneal thickness (CCT) was obtained by Orbscan. Intraocular pressure was taken by GAT, DCT and ORA in a randomised order. Mean intraocular pressure was taken by each device and correlation to CCT was analysed. Mean CH and CRF and their correlation to CCT were calculated.
Mean intraocular pressure was 16.5mmHg (± 4.4mmHg standard deviation) obtained by GAT, 18.2 mmHg (± 4.2mmHg) by DCT and 20.6mmHg (± 6.1mmHg) by ORA measurement. NTG subjects had a significantly (p = 0.005) thinner CCT (506 ± 55 µm) than POWG subjects (567 ± 53 µm). Subjects with OHT showed non-significant higher CCT values (592 ± 41 µm). Bland-Altman-Analysis revealed a good correlation for DCT and GAT, while ORA yielded significantly higher IOP values than DCT (+2,4mmHg, SD +2,3mmHg) and especially GAT (+4,2mmHg, SD +2,3mmHg). Neither ORA nor GAT showed a correlation to CCT (r² = 0.07 in DCT and r² = 0.08 in ORA) while GAT showed a weak dependency (r² = 0.12). There was no correlation between CH and CCT (r² = 0.01), but a weak correlation between CRF and CCT (r² = 0.2). CRF was significantly higher in subjects with OHT (11.6 ± 2.2) than in subjects with POWG (9.6 ± 2.0) (p = 0.006). For CH, there was no difference between the groups.
ORA yielded higher IOP values than both DCT and GAT. The difference increased with higher IOP values. ORA and DCT showed no dependency on CCT. CH is independent on CCT, while CRF had a positive correlation with CCT. Further studies to examine the importance of CH and CRF and other biomechanical properties of the cornea in the measurement of intraocular pressure will be needed.
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