The inclusion of the epithelium in numerical models of the human cornea.

We present a patient-specific finite element model of the human cornea that accounts for the presence of the epithelium. The thin anterior layer that protects the cornea from the external actions has a scant relevance from the mechanical point of view, and it has been neglected in most numerical models of the cornea, which assign to the entire cornea the mechanical properties of the stroma. Yet, modern corneal topographers capture the geometry of the epithelium, which can be naturally included into a patient-specific solid model of the cornea, treated as a multi-layer solid.

Progressive high-fluence epithelium-on accelerated corneal crosslinking: a novel corneal photodynamic therapy for early progressive keratoconus.

Purpose: To assess the preliminary clinical results of a new, progressively higher fluence-pulsed light Epi-On accelerated crosslinking nomogram (PFPL M Epi-On ACXL) in the treatment of progressive keratoconus (KC).

Setting: Siena Crosslinking Center, Siena, Italy.

Methods: A prospective pilot open, non-randomized interventional study, including 32 eyes of 32 young-adult patients over 26 years old with Stages I-III progressive KC undergoing PFPL M Epi-On ACXL, was conducted.

Modeling the biomechanics of laser corneal refractive surgery.

We present a finite element model of the human cornea used to simulate corneal refractive surgery according to the three most diffused laser procedures, i. e., photo-refractive keratectomy (PRK), laser in-situ keratomileusis (LASIK) and small incision lenticule extraction (SMILE).

Evaluation of the Efficacy of Low-Particle-Size Toothpastes against Extrinsic Pigmentations: A Randomized Controlled Clinical Trial.

Stain-removing domiciliary protocols are focused on the elimination of dental extrinsic pigmentations by the application of abrasive toothpastes, extensively available in commerce. The goal of the present study is to evaluate the efficacy of two different stain removal molecule-formulated toothpastes by the reduction of clinical parameters: the micro-cleaning crystals and activated charcoal. A total of 40 participants with extrinsic dental pigmentations were enrolled and divided into two groups: a Control group, assigned to a toothpaste with micro-cleaning crystals (Colgate Sensation White); and a Trial group, with microparticle-activated charcoal toothpaste (Coswell Blanx Black).

Experimental in-vitro investigation on Epi-Off-Crosslinking on porcine corneas.

Aim: To evaluate quantitatively the effects of the Epi-Off-CXL irradiance dose on the stromal stiffening of pig corneas.

Setting: Laboratory of Biological structures (LaBS), Politecnico di Milano, Milano, Italy.

Methods: Inflation tests have been carried on 90 excised and de-epithelized pig corneas, monitoring the change of configuration of the corneal dome at specific pressures.

A numerical model of capsulorhexis to assess the relevance of size and position of the rhexis on the IOL decentering and tilt.

Finite element models of human crystalline capsular bag and zonular fibers are used to estimate the mechanical response of the capsule to the presence of a C-loop Intra-Ocular Lens (IOL) after cataract surgery, to assess the influence of capsulorhexis size, shape and location on IOL decentration and tilt. The model includes, in the anterior capsule, a hole with variable size, shape and position, which represents the rhexis obtained in a manual or laser-assisted manner. The IOL is not explicitly modelled, but its action is reproduced by means of a set of elastic ties, connecting the opposite sides of the bag and exerting the force corresponding to an expanded IOL.

Cornea modelling.

Background: Biomechanics introduces numerous technologies to support clinical practice in ophthalmology, with the goal of improving surgical outcomes and to develop new advanced technologies with minimum impact on clinical training. Unfortunately, a few misconceptions on the way that computational methods should be applied to living tissues contributes to a lack of confidence towards computer-based approaches.

Methods: Corneal biomechanics relies on sound theories of mechanics, including concepts of equilibrium, geometrical measurements, and complex material behaviors.

A 3D fluid-solid interaction model of the air puff test in the human cornea.

We present a numerical model of a contactless test commonly used to assess the biomechanics of the human cornea. The test, consisting in a rapid air jet applied to the anterior surface of the cornea, is controversial. Although the numerous studies documented in the literature have not been able yet to clarify its relevance as a diagnostic tool, the test has the potential to be combined with inverse analysis procedures to characterize the parameters of numerical models of the cornea.

Modelling with a meshfree approach the cornea-aqueous humor interaction during the air puff test.

The air puff test is an in-vivo investigative procedure commonly utilized in ophthalmology to estimate the intraocular pressure. Potentially the test, quick and painless, could be combined with inverse analysis methods to characterize the patient-specific mechanical properties of the human cornea. A rapid localized air jet applied on the anterior surface induces the inward motion of the cornea, that interacts with aqueous humor-the fluid filling the narrow space between cornea and iris-with a strong influence on the dynamics of the cornea.

Myopic Surface Ablation in Asymmetrical Topographies: Refractive Results and Theoretical Corneal Elastic Response.

Purpose: To evaluate refractive results and the theoretical elastic response of photorefractive keratectomy in eyes with asymmetrical corneal surface and to compare such outcomes with a control-matched group of normal topographies.

Design: Retrospective interventional case series with matched comparison group.

Methods: Thirty eyes with superior-inferior dioptric difference (SI index) > 1.

Coupled electro-mechanical models of fiber-distributed active tissues.

We discuss a constitutive model for stochastically distributed fiber reinforced tissues, where the active behavior of the fibers depends on the relative orientation of the electric field. Unlike other popular approaches, based on numerical integration over the unit sphere, or on the use of second order structure tensors, for the passive behavior we adopt a second order approximation of the strain energy density of the distribution. The purely mechanical quantities result to be dependent on two (second and fourth order, respectively) averaged structure tensors.

The influence of intraocular pressure and air jet pressure on corneal contactless tonometry tests.

The air puff is a dynamic contactless tonometer test used in ophthalmology clinical practice to assess the biomechanical properties of the human cornea and the intraocular pressure due to the filling fluids of the eye. The test is controversial, since the dynamic response of the cornea is governed by the interaction of several factors which cannot be discerned within a single measurement. In this study we describe a numerical model of the air puff tests, and perform a parametric analysis on the major action parameters (jet pressure and intraocular pressure) to assess their relevance on the mechanical response of a patient-specific cornea.

Customized Finite Element Modelling of the Human Cornea.

Aim: To construct patient-specific solid models of human cornea from ocular topographer data, to increase the accuracy of the biomechanical and optical estimate of the changes in refractive power and stress caused by photorefractive keratectomy (PRK).

Method: Corneal elevation maps of five human eyes were taken with a rotating Scheimpflug camera combined with a Placido disk before and after refractive surgery. Patient-specific solid models were created and discretized in finite elements to estimate the corneal strain and stress fields in preoperative and postoperative configurations and derive the refractive parameters of the cornea.

A Newly Developed Tri-Leaflet Polymeric Heart Valve Prosthesis.

The potential of polymeric heart valves (PHV) prostheses is to combine the hemodynamic performances of biological valves with the durability of mechanical valves. The aim of this work is to design and develop a new tri-leaflet prosthetic heart valve (HV) made from styrenic block copolymers. A computational finite element model was implemented to optimize the thickness of the leaflets, to improve PHV mechanical and hydrodynamic performances.

Biomechanical and optical behavior of human corneas before and after photorefractive keratectomy.

Purpose: To evaluate numerically the biomechanical and optical behavior of human corneas and quantitatively estimate the changes in refractive power and stress caused by photorefractive keratectomy (PRK).

Setting: Athineum Refractive Center, Athens, Greece, and Politecnico di Milano, Milan, Italy.

Design: Retrospective comparative interventional cohort study.

The influence of the geometry of the porcine cornea on the biomechanical response of inflation tests.

To withstand the high probability of success, the growing diffusion of laser surgery for the correction of visual defects, corneal surgeons are regarding with interest numerical tools able to provide reliable predictions of the intervention outcomes. The main obstacle to the definition of a predictive numerical instrument is the objective difficulty in evaluating the in vivo mechanical properties of the human cornea. In this study, we assess the ability of a parametrised numerical model of the cornea (Pandolfi and Manganiello 2006) to describe individual pressurisation tests on whole porcine corneas once the mechanical parameters of the model have been calibrated over average data.

Three-dimensional modeling and computational analysis of the human cornea considering distributed collagen fibril orientations.

Experimental tests on human corneas reveal distinguished reinforcing collagen lamellar structures that may be well described by a structural constitutive model considering distributed collagen fibril orientations along the superior-inferior and the nasal-temporal meridians. A proper interplay between the material structure and the geometry guarantees the refractive function and defines the refractive properties of the cornea. We propose a three-dimensional computational model for the human cornea that is able to provide the refractive power by analyzing the structural mechanical response with the nonlinear regime and the effect the intraocular pressure has.