Comparison of mechanical properties of keratoconus and normal corneas.

Abstract In order to measure more directly the physical properties of the corneoscleral shell in keratoconus, mechanical stress-strain tests were performed on strips of human cornea. Rectangular human corneal samples were glued to the arms of an extensiometer, a technique that avoids the problems of slippage and compression found with conventional clamps. Strain was measured using an electromagnetic displacement probe. The entire apparatus was immersed in a thermoregulated mineral oil bath to maintain constant corneal hydration. The resultant data obey the relation σ = A [e αϵ −1]. Stiffening constants α ranged from 34 to 82. We found that there are significant differences in the parameters for the two groups, with keratoconus corneas yielding lower α and higher A values than the normal controls. However, within the physiological range these differences offset so that there is no difference in the overall elastic behaviour of the keratoconus and normal corneas. Creep tests at constant load were also performed on normal and keratoconus corneas.

[1]  G. V. Alphen,et al.  The Elasticity of Sclera and Choroid of the Human Eye, and Its Implications on Scleral Rigidity and Accommodation , 1977 .

[2]  Kulund Dn,et al.  Scleral creep in vitro resulting from cyclic pressure pulses: applications to myopia. , 1981 .

[3]  Mark Hh.  Keratoconus appearing after contact lens wear. , 1974 .

[4]  J. Hartstein.  Keratoconus that developed in patients wearing corneal contact lenses. Report of four cases. , 1968, Archives of ophthalmology.

[5]  B. Becker,et al.  Research into the pathogenesis of keratoconus. A new syndrome: low ocular rigidity, contact lenses, and keratoconus. , 1970, Archives of ophthalmology.

[6]  P. Greene.  Mechanical Considerations in Myopia: Relative Effects of Accommodation, Convergence, Intraocular Pressure, and the Extraocular Muscles , 1980, American journal of optometry and physiological optics.

[7]  Poole Ta.  Calculation of stress distribution in keratoconus. , 1973 .

[8]  C. Foster,et al.  Ocular rigidity in keratoconus. , 1978, American journal of ophthalmology.

[9]  T. McMahon,et al.  Scleral creep vs. temperature and pressure in vitro. , 1979, Experimental eye research.

[10]  H. Oxlund,et al.  Biomechanical properties of keratoconus and normal corneas. , 1980, Experimental eye research.

[11]  M Ruben,et al.  Aetiology of keratoconus. , 1976, The British journal of ophthalmology.

[12]  P. Davies,et al.  The paretic pupil: its incidence and aetiology after keratoplasty for keratoconus. , 1975, The British journal of ophthalmology.

[13]  W. A. Schlegel,et al.  Nonlinear material properties of intact cornea and sclera. , 1972, Experimental eye research.