10 January 1996 Laser thermokeratoplasty: determination of biomechanical properties of the cornea
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Laser thermokeratoplasty (LTK) is a minimally invasive method to correct hyperopia and astigmatism. The alteration in refractive power of the eye is achieved by thermally induced shrinkage of stromal collagen in the corneal periphery with a mid-IR laser system ((lambda) equals 1.4 - 2.5 micrometers ) and thereby mechanically increasing the central corneal curvature. In order to evaluate the best choice of laser parameters and exposure geometry a mechanical model of the cornea, which is highly dependent on the material parameters of the corneal tissue, is to be developed. For this reason uniaxial tensile tests were performed on specimens of porcine cornea to determine their nonlinear stress-strain relations and their viscoelastic behavior. Laser induced stress has been measured while corneal stripes were being exposed to a pulsed Cr:Tm:Ho:YAG laser ((lambda) equals 2.12 micrometers ) system. The stresses observed correlated just beyond the threshold qualitatively well with the number of applied pulses. For larger pulse energies the stress stabilized after a few pulses, which means further laser application could neither increase nor decrease the level of stress. After the end of the last laser pulse the specimens relaxed within several minutes down to a level of residual stress, which is probably to be held responsible for the refractive change in LTK.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Juergen Kampmeier, Juergen Kampmeier, Ralf Brinkmann, Ralf Brinkmann, Reginald Birngruber, Reginald Birngruber, } "Laser thermokeratoplasty: determination of biomechanical properties of the cornea", Proc. SPIE 2624, Laser-Tissue Interaction and Tissue Optics, (10 January 1996); doi: 10.1117/12.229564; https://doi.org/10.1117/12.229564

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