The role of viscoelasticity and stress gradients on the outcome of conductive keratoplasty

Abstract

A mechanical analysis of the conductive keratoplasty on hyperopic eyes has been carried out, and the attention has been focused on incorporating the actual viscoelastic properties of the human corneal tissue and on the stress gradients induced by the intervention. By avoiding unnecessary complications which may obscure the essential behaviour of the model, the results are in very good agreement with the clinical and experimental findings and suggest that the major role in the commonly observed decrease of the initial degree of the refractive correction might be played by the stress gradients at the intervention spots, which are likely to influence the wound-healing. The study aims to contribute some firm mechanical roots to the predictability of the outcome of an increasingly popular technique that, notwithstanding several advantages with respect to ablative interventions, at present cannot be considered completely satisfactory.

Shear Behavior of Bovine Scleral Tissue

“…Ocular tissue properties, in particular those of the sclera and cornea, are important for the study of diseases such as keratoconus and glaucoma [1][2][3][4][5][6][7][8], the eye's response to nominal and severe loading [9][10][11][12][13][14][15], and possibly the eye's development [16]. Tensile stress-strain properties of ocular tissues have been determined by tests in traditional machines using excised "dog-bone" or strip shaped specimens.…”

Finite element modelling of cornea mechanics: a review

“…The results obtained from their boundary assumption were similar to the results obtained for the whole eye. Other studies (11,37,38) adopted similar boundary conditions for their corneal models. Roy et al (14) created the whole eye model and compared the displacement results with those for the corneal model with fixed sclera to show that the corneoscleral limbus plays an important part in predicting the response to refractive surgery.…”

“…Researchers in (13) investigated boundary conditions (a), (b), and (c). D) The cornea is allowed to expand along a given surface, as in (11,23,37,38) . Forty degrees from horizontal is taken as a typical angle.…”

“…Refractive surgeries on the periphery of the cornea, such as conductive keratoplasty (CK) and intracorneal rings (ICR), have recently attracted more interest. These surgeries are primarily performed on hyperopic eyes that require steepening rather than flattening of the corneal surface (38) . FEA has potential usefulness as a simulation tool for refractive surgery planning using accurate in vivo corneal material properties and geometry data (14) .…”

“…Jo et al (19) developed a 3D FE model, including the cornea, aqueous humor, and RF electrodes, to investigate the resultant thermal damage during RF heating in the CK procedure. Fraldi et al (38) also presented a viscoelastic FEA to study the mechanical response of the hyperopic cornea to CK and assess the postsurgical stability of the applied refractive correction. Hameed et al (53) created a 3D FE model to simulate the ISPRK technique for correcting myopic corneas and predicting treatment outcomes.…”