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E. Lanchares Sancho, F. Palos, B. Calvo, R. Navarro, M. Doblare; Opto-Mechanical Model of Curved Incisions for Astigmatism Correction. Invest. Ophthalmol. Vis. Sci. 2008;49(13):671.
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To develop a realistic model of the opto-mechanical behaviour of the cornea after curved relaxing incisions, and compare the model with the Lindstrom’s nomogram.
A three-dimensional finite element model was generated from the anterior half ocular globe geometry. The corneal tissue was modeled as a quasi-incompressible, anisotropic hyperelastic constitutive behaviour strongly dependent on the physiological collagen fibril distribution. With this model we simulated the effects of curved corneal incisions, according to Lindstrom’s nomogram, where the number and length of incisions depend on the diopters of astigmatism to correct. The resulting geometry of the optical zone was analyzed and finite ray tracing performed to compute refractive power and HOA.
The finite element simulation provides the displacements of the nodes and from that we obtain the resulting elevation topography. Results of finite ray tracing show a close agreement between the model and the Lindstrom’s nomogram, whereas paraxial computation yields a significant undercorrection of astigmatism. Arcuates induce HOA, mainly coma, trefoil and quadrafoil.
A tool has been developed to simulate incisions for astigmatism correction to provide a technical evidence for the surgeon to make his decision while planning the surgery or designing new incisional techniques. The close agreement found between model and nomogram supports the validity of this approach. Paraxial formulas fail to predict the resulting astigmatism.
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