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Corneal Biomechanics and Refractive Surgery

Les comparto el capítulo de libro bajo la co-autoría con el profesor Fabio Ariel Guarnieri:

Biomechanical Instrumentation in Refractive Surgery

The determination of the intraocular pressure by means of instruments is still a developing science. Several physical properties and mechanisms affect this measure due to the corneal shape and its rigidity. Experimental and analytical researches are tools to improve indirect technologies (tonometric devices) for this relevant quantity for ophthalmologic diagnosis. In this chapter the applanation contact tonometry is the main subject (biomechanical modeling, computational modeling, and calibration equations); nevertheless, new tonometric devices tend to avoid contact to diminish influence of probe shape in the contact procedure and also pain in the patient.

Intraocular Pressure: Goldmann Tonometry, Computational Model, and Calibration Equation

Abstract: Purpose: There exists a concern about the general accuracy of intraocular pressure (IOP) measurements using tonometry, and especially Goldmann applanation tonometer (GAT) because it considers the cornea as an infinite thin shell. In this study, the relationship between the true IOP and tonometric IOP, external curvature radius (ECR), and central corneal thickness (CCT) is explored.

Methods: In this study, the calibration of the IOP measurements through GAT for different values of CCT, ECR, and E (Young modulus), is done through computational simulations of the mechanical behavior of the cornea subjected to the applanation process using the finite element method (FEM). Previous to this simulations, experimentations on rabbits were performed to confirm that inaccurate readings are obtained with GAT in certain conditions. This methodology is also followed to establish the range of corneal parameters of patients for which the GAT measure of pressure is reliable. The calibration equation for GAT measurements is developed from a statistical multiple linear regression analysis.

Results: Based on a statistical variable analysis of the computational modeling results, a calibration equation is established for the GAT that relates the true IOP with the ECR, CCT, and GAT measurements.

Conclusions: Our results show that GAT measures are linearly dependent on the modulus of elasticity of the cornea; nevertheless, if we consider a healthy cornea with a specific modulus of elasticity, it is possible to correct the measure with a linear equation involving CCT and ECR.

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