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Analysis of Biomechanical Waveform Measurement Associated with Glaucoma Progression

Analysis of Biomechanical Waveform Measurement Associated with Glaucoma Progression. Seungjoo Ha, M.D. Department of Ophthalmology, Soonchunhyang University Hospital, Seoul, Korea. The authors have no financial interest in the subject matter of this poster. Purpose.

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Analysis of Biomechanical Waveform Measurement Associated with Glaucoma Progression

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  1. Analysis of Biomechanical Waveform Measurement Associated with Glaucoma Progression Seungjoo Ha, M.D. Department of Ophthalmology, Soonchunhyang University Hospital, Seoul, Korea The authors have no financial interest in the subject matter of this poster.

  2. Purpose • A new measure of corneal biomechanics, called corneal hysteresis, assesses corneal resistance to deformation. • The Ocular Response Analyzer (ORA, Reichert Ophthalmic Instruments, Depew, NY) is a new instrument that measures corneal hysteresis, the corneal biomechanical response to rapid indentation by an air jet. • This study compared measurements of the Ocular Response Analyzer (ORA) to determine their association with glaucoma progression. • Figure 1. Ocular Response Analyzer Measurement Signal. • Corneal hysteresis is the difference in applanation pressures between the rising and falling phases of the air jet.

  3. Methods 110 eyes of 110 patients POAG & NTG Group 1 (Non-progression Glaucoma) 64 eyes Group 2 (Progression Glaucoma) 46 eyes • Progression Glaucoma Criteria • 1) Optic disc hemorrhage • 2) Humphrey visual field change • (According to Hodapp-Parrish-Anderson criteria) • - New detection of visual field defect • - Progression of previous visual field defect • ORA (Ocular Response Analyzer) parameters • CH (Corneal hysteresis) • CRF (Corneal resistance factor) • IOPg (Goldmann-correlated IOP) • IOPcc (Corneal-Compensated IOP) • Other test • GAT (Goldmann applanation tonometer) • DCT (Dynamic contour tonometer) • NCT (Noncontact tonometer) • CCT (Central corneal thickness) Figure 2. Schemes of subjects and methods

  4. Result Table 1. Baseline characteristics

  5. Result • The confidence intervals of CH measurements of the progression cohort and the non-progression cohort were 10.60±1.45 and 9.95±1.31, respectively, showing a statistically significant difference (p<0.020) (Table 2). • The confidence intervals of the IOPcc measurements were 12.55±2.66 and 14.12±3.25for the non-progression and progression groups, respectively (p<0.008) (Table 2). • However, the ORA measurements of CRF and IOPg were not significantly difference between the two groups. (Table 2). Table 2. Comparison of measurements using ORA between the two groups (*: by Independent-Samples T test)

  6. Result Table 3. Comparison of other measurements between the two groups (*: by Independent-Samples T test) Figure 3. Comparison of all measurement values between the two groups (*P<0.05 by Independent-Samples T test)

  7. Result • The odds ratios of the progressed cohort to the non-progression cohort for CH, IOPcc, GAT, and DCT measurements were 1.67, 2.37, 1.44, and 1.86, respectively, with IOPcc exhibiting the highest value (p<0.029) (Table 4). Table 4. Odd ratio of the measurements (CH, IOPcc, GAT, DCT) between the two groups

  8. Conclusion • There were significant associations between glaucoma progression measured by the ORA for CH and IOPcc measures. • Among the two, the IOPcc showed a greater odds ratio for intraocular pressure than the GAT or the DCT measures and can be used as a useful measure to detect glaucoma progression. • Corneal hysteresis is a measure of viscous damping in the corneal tissue and the energy absorption capability of the cornea. • CRF is a measurement of the cumulative effects of both the viscous and elastic resistance encountered by the air jet and represents the overall resistance (rigidity) of the cornea.

  9. Conclusion • In the progression glaucoma group, CH was lower and IOPcc was higher, but CCT was thicker than the non-progression glaucoma group. • Unlike previous theories that emphasize the central corneal thickness as a risk factor for glaucoma, among various characteristics of corneal thickness (including thickness, viscous damping, elastic property) the viscous damping (maybe a representative indicator of intraocular pressure of the lamina cribrosa) should be investigated further considering its significant association with glaucoma progression found in this study. • Furthermore, a larger randomized and prospective case-control study on the correlation of ORA and glaucoma progression will be necessary.

  10. References • Anthony PW, et al. Corneal Hysteresis but Not Corneal Thickness Correlates With Optic Nerve Surface Compliance in Glaucoma Patinets. IOVS 2008;49(8):3262-8. • David T, et al. Correlations between corneal hysteresis, intraocular pressure, and corneal central pachymetry. J Cataract Refract Surg 2008;34:616-22. • Aachal Kotecha. What Biomechanical Properties of the Cornea Are Relevant for the Clinician? Surv Ophthalmol 2007;52(Suppl 2):S109-14.

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