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Shuai-Chun Lin, Arash Kazemi, Jay W McLaren, Sayoko Eileen Moroi, Carol B Toris, Arthur J Sit; Relationship between Ocular Rigidity, Corneal Hysteresis, and Corneal Resistance Factor. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):6137.
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© ARVO (1962-2015); The Authors (2016-present)
The risk of developing glaucoma has been suggested to be associated with abnormal biomechanical properties. Two biomechanical variables, corneal hysteresis (CH) and the corneal resistance factor (CRF), can be measured clinically. However, it is not clear how these relate to known biomechanical properties such as ocular rigidity. In this study we compared measurements of ocular rigidity (E) with CH and CRF.
Fifty eyes of 25 healthy subjects (age 41-67 years, mean 50 years) were studied. CH and CRF were measured (Ocular Response Analyzer, Reichert Inc.) in each eye. IOP was measured in the sitting position by pneumatonometry (Model 30 Classic, Mentor). After 5 minutes, IOP was measured in the supine position (P0) and then with a 10-gram weight for 2 minutes. The initial weighted IOP (P1) was calculated from a second-order polynomial fitted to the recorded pressures. The ocular rigidity, E, was the ratio of the log of the initial pressure difference (P1 - P0) and the ocular volume change (∆V) as determined by using Friedenwald nomograms. Correlations between E and CH and between E and CRF were examined by Pearson correlation. Significances of correlation were determined by using generalized estimating equation models to account for the possible correlation between fellow eyes.
Ocular rigidity (E) was negatively correlated with CRF (r=-0.41, p= 0.02) and sitting IOP (r=-0.48, p<0.001); the regression equation with CRF was E = - 0.0013 x CRF + 0.042. Corneal hysteresis was not correlated with ocular rigidity (p=0.39).
The relationship between ocular rigidity and CRF suggests that CRF primarily reflects ocular tissue elasticity. In contrast, CH is not associated with ocular rigidity and likely reflects tissue viscosity. The relationship between ocular rigidity, corneal hysteresis, and the corneal resistance factor will provide a basis for understanding the relationships between biomechanical variables and their changes in eye diseases.
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