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J. Wang, M. Chagnon, A. Bayoumi, M. Wajszilber, D. Descovich, M. R. Lesk; Correlation Between Glaucoma Damage, Ocular Biomechanical Properties and Vasospasm. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4599.
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© ARVO (1962-2015); The Authors (2016-present)
To study the relationship between biomechanical properties of the eye and degree of glaucoma damage in vasospastic and non-vasospastic subjects across the spectrum of glaucoma.
Cross sectional clinical study. Patients with diagnosis of ocular hypertension (OHT), glaucoma suspect and open angle glaucoma (OAG) were recruited prospectively from a glaucoma clinic. Control subjects were recruited from a community-based screening program. All subjects were evaluated bilaterally for historical Tmax (maximum known IOP), dynamic contour tonometry (DCT), corneal hysteresis (CH), central corneal thickness (CCT), axial length (AL), Heidelberg Retina Tomography (HRT) of the optic nerve head, and finger Doppler blood flow response to 4°C water immersion. Vasospasticity was defined as a maximum/minimum flow ratio ≥ 7. Wall stress using Laplace’s equation was calculated in each subject; we also incorporated CH into the equation. Correlation analysis was performed between mean defect (MD) on standard automated perimetry, HRT parameters (rim area, rim volume, GPS score) and ocular biomechanical parameters (Tmax, CCT, AL, CH, wall stress) in the vasospastic and non-vasospastic groups.
126 subjects were recruited prospectively including 22 normal subjects, 36 OHT, 23 subjects with suspect discs, and 45 glaucoma patients with established visual field damage. Low CH, low CCT, and long AL correlated with more advanced ONH damage using key HRT parameters (GPS or rim Volume, p-values 0.001 to 0.01). Tmax, calculations of wall stress using Laplace’s Law, without or with incorporation of CH, and AL were positively correlated with worse MD (p-values 0.000 to 0.030). All correlations were stronger in the non-vasospastic cohort (n = 63) except axial length that was stronger in the vasospastic cohort (n = 53).
Lower CH (a more viscoelastic cornea) alone or as part of a wall stress calculation correlates with degree of glaucoma damage. CH, CCT, IOP and wall stress calculations correlate better with glaucoma damage in non-vasospastic patients while axial length correlates better with glaucoma damage in vasospastic patients. This data suggests different pathogenic mechanisms of glaucoma in these different populations.
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