Assessment of the association between In vivo corneal morphogeometrical changes and keratoconus eyes with severe visual limitation

Assessing changes suffered by the cornea as keratoconus progresses has proven to be vital for this disease diagnosis and treatment. 'is study determines the corneal biometric profile in eyes considered as affected by keratoconus (KC) showing severe visual limitation, by means of in vivo 3D modelling techniques. 'is observational case series study evaluated new objective indices in 50 healthy and 30 KC corneas, following a validated protocol created by our research group, which has been previously used for diagnosis and characterization of KC in asymptomatic (preclinical) and mild visually impaired eyes. Results show a statistically significant reduction of corneal volume and an increase of total corneal area in the severe KC group, being anterior and posterior corneal surfaces minimum thickness points the best correlated parameters, although with no discrimination between groups. Receiving operator curves were used to determine sensitivity and specificity of selected indices, being anterior and posterior apex deviations the ones which reached the highest area under the curve, both with very high sensitivity (96.7% and 90%, respectively) and specificity (94.0% and 99.9%, respectively). 'e results suggest that once severe visual loss appears, anterior corneal topography should be considered for a more accurate diagnosis of clinical KC, being anterior apex deviation the key metric discriminant. 'is study can be a useful tool for KC classification, helping doctors in diagnosing severe cases of the disease, and can help to characterize corneal changes that appear when severe KC is developed and how they relate with vision deterioration.This publication has been carried out in the framework of the Thematic Network for Cooperative Research in Health (RETICS) reference number RD16/0008/0012 financed by the Carlos III Health Institute-General Subdirection of Networks and Cooperative Investigation Centers (R&D&I National Plan 2013–2016) and the European Regional Development Fund (FEDER)

Geometric modelling of the human cornea: A new approach for the study of corneal ectatic disease. A pilot investigation

The aim of this study was to describe the application of a new bioengineering graphical technique based on geometric custom modelling capable to detect and to discriminate small variations in the morphology of the corneal surface. A virtual 3D solid custom model of the cornea was obtained employing Computer Aided Geometric Design tools, using raw data from a discrete and finite set of spatial points representative of both sides of the corneal surface provided by a corneal topographer. Geometric reconstruction was performed using B-Spline functions, defining and calculating the representative geometric variables of the corneal morphology of patients under clinical diagnosis of keratoconus

Efficacy of morpho-geometrical analysis of the corneal surfaces in keratoconus disease according to moderate visual limitation

The cornea is a complex hemispheric structure, made of collagen fibres that provide it a homogenous and stable geometry. During keratoconus disease, a loss of tenacity takes place in the collagen fibres that form the corneal structure, producing an alteration of its geometry, this is, a change of its curvature, and therefore, a loss of visual quality of patients. The geometric characterization of the hemispheric structure by means of biometric parameters is a very solid technique of diagnosis, based in a virtual 3D model, which has already been validated for several degrees of severity of keratoconus pathology. In this prospective comparative study, 93 corneas (50 healthy subjects and 43 patients with keratoconus with moderate visual limitation) were geometrically modelled. The results obtained in this work suggest that the best predictive biometric parameters are anterior corneal surface area and posterior apex deviation, and that the strongest correlation is produced between sagittal plane apex area in minimum thickness point and sagittal plane apex area. The studied biometric parameters have shown significant differences between groups. Therefore, the analysis of the biometric parameters that register the geometric decompensation that locally appear in a corneal region, as a response to the asymmetry produced during the development of keratoconus disease with a moderate visual impairment, is a new approach that may lead to a better understanding of the disease with this degree of optical limitation.This publication has been carried out in the framework of the Thematic Network for Co-Operative Research in Health (RETICS) reference number RD16/0008/0012 financed by the Carlos III Health Institute-General Subdirection of Networks and Cooperative Investigation Centres (R&D&I National Plan 2013-2016) and the European Regional Development Fund (FEDER)

Detection of subclinical keratoconus using biometric parameters

The validation of innovative methodologies for diagnosing keratoconus in its earliest stages is of major interest in ophthalmology. So far, subclinical keratoconus diagnosis has been made by combining several clinical criteria that allowed the definition of indices and decision trees, which proved to be valuable diagnostic tools. However, further improvements need to be made in order to reduce the risk of ectasia in patients who undergo corneal refractive surgery. The purpose of this work is to report a new subclinical keratoconus detection method based in the analysis of certain biometric parameters extracted from a custom 3D corneal model. This retrospective study includes two groups: the first composed of 67 patients with healthy eyes and normal vision, and the second composed of 24 patients with subclinical keratoconus and normal vision as well. The proposed detection method generates a 3D custom corneal model using computer-aided graphic design (CAGD) tools and corneal surfaces’ data provided by a corneal tomographer. Defined bio-geometric parameters are then derived from the model, and statistically analysed to detect any minimal corneal deformation. The metric which showed the highest area under the receiver-operator curve (ROC) was the posterior apex deviation. This new method detected differences between healthy and sub-clinical keratoconus corneas by using abnormal corneal topography and normal spectacle corrected vision, enabling an integrated tool that facilitates an easier diagnosis and follow-up of keratoconus.This publication has been carried out in the framework of the Thematic Network for Co-Operative Research in Health (RETICS) reference number RD16/0008/0012 financed by the Carlos III Health Institute-General Subdirection of Networks and Cooperative Investigation Centers (R&D&I National Plan 2013–2016) and the European Regional Development Fund (FEDER)

Comparison of corneal morphologic parameters and high order aberrations in keratoconus and normal eyes

The aim of this study is evaluating the influence of corneal geometry in the optical system’s aberrations, and its usefulness as diagnostic criterion for keratoconus.159 normal eyes (normal group, mean age 37.8 ± 11.6 years) and 292 eyes with the diagnosis of keratoconus (keratoconus group, mean age 42.2 ± 17.6 years) were included in this study. All eyes received a comprehensive ophthalmologic examination. A virtual 3D model of each eye was made using CAD software and different anatomical parameters related with surface and volume were measured. Statistically significant differences were found for all anatomical parameters (all p < 0.001). AUROC analysis showed that all parameters reached values above 0.7, with the exception of the total corneal surface area (TCSAA-S). In conclusion, the methodology explained in this research, that bases in anatomical parameters obtained from a virtual corneal model, allow to analyze the diagnostic value of corneal geometry correlation with optical aberrations in keratoconus pathology.This publication has been carried out in the framework of the Thematic Network for Co-Operative Research in Health (RETICS), reference number RD16/0008/0012, financed by the Carlos III Health Institute–General Subdirection of Networks and Cooperative Investigation Centers (R&D&I National Plan 2013–2016) and the European Regional Development Fund (FEDER)

3D printed personalized corneal models as a tool for improving patient’s knowledge of an asymmetric disease

Additive manufacturing is a vanguard technology that is currently being used in several fields in medicine. This study aims to evaluate the viability in clinical practice of a patient-specific 3D model that helps to improve the strategies of the doctor-patient assistance. Data obtained from a corneal topographer were used to make a virtual 3D model by using CAD software, to later print this model by FDM and get an exact replica of each patient’s cornea in consultation. Used CAD and printing software were open-source, and the printing material was biodegradable and its cost was low. Clinic users gave their feedback by means of a survey about their feelings when perceiving with their senses their own printed cornea. There was 82 surveyed, 73.8% (9.74; SD: 0.45) of them considered that the model had helped them a lot to understand their disease, expressing 100% of them their intention of taking home the printed model. The majority highlighted that this new concept improves both quality and clinical service in consultation. Custom-made individualized printed models allow a new patient-oriented perspective that may improve the communication strategy from the ophthalmologist to the patient, easing patient’s understanding of their asymmetric disease and its later treatment.This publication has been carried out in the framework of the Thematic Network for Co-Operative Research in Health (RETICS), reference number RD16/0008/0012, financed by the Carlos III Health Institute–General Subdirection of Networks and Cooperative Investigation Centers (R&D&I National Plan 2013–2016) and the European Regional Development Fund (FEDER)

Análisis morfogeométrico de la estructura hemiesférica del segmento anterior del ojo humano y su aplicación clínica

[SPA] Esta tesis doctoral se presenta bajo la modalidad de compendio de publicaciones.La superficie refractiva más importante del ojo humano es la córnea, que presenta una estructura de forma hemiesférica localizada en el segmento ocular anterior. Esta estructura, incluso en un escenario no patológico, no es perfecta, dado que presenta asimetrías que provocan deformaciones, desalineamientos y descentramientos entre ambos ojos del mismo individuo. Cuando además existen patologías corneales, como pueden ser las ectasias, esta asimetría, y por tanto sus efectos, se acentúan, provocando en el paciente un deterioro ciertamente importante de la capacidad visual, lo que da cuenta de la importancia de disponer de sistemas que permitan una caracterización corneal precisa que facilite la detección, diagnóstico y clasificación de las ectasias. En esta tesis doctoral se ha propuesto un sistema integrado capaz de detectar (fase preclínica) y diagnosticar (fase clínica), de manera eficiente y desde un punto de vista óptico-geométrico, la progresión de la ectasia corneal, permitiendo de esta forma incidir de manera directa en el proceso de toma de decisiones relativas a la calidad visual de los pacientes. Para ello, y partiendo de un modelo sólido personalizado en 3D generado con herramientas de Diseño Asistido por Ordenador, se han propuesto diversos parámetros morfogeométricos macroscópicos de tipo lineal, superficial, volumétrico y angular, con el objetivo de caracterizar la progresión de la ectasia corneal más importante, el denominado queratocono. La estructura microscópica también se ha estudiado, programando una aplicación que permite cuantificar el polimegatismo y el pleomorfismo de las células endoteliales corneales. Posteriormente, se han revisado los distintos sistemas univariantes y multivariantes de diagnóstico y clasificación del queratocono, y se ha comprobado que los parámetros morfogeométricos permiten tanto la detección como la clasificación del queratocono en base a su grado de severidad de acuerdo con las escalas RETICS, Amsler-Krumeich y Alió-Shabayek. Además, se han propuesto dos modelos predictivos (demográfico-óptico-geométricos) de clasificación del grado de la enfermedad en base a la escala RETICS, que han dado lugar al desarrollo de dos aplicaciones informáticas denominadas EMKLAS y KERATOSCORE, que a su vez dan cuenta de la dificultad inherente a la detección de esta enfermedad en la fase preclínica. Por último, se ha aplicado un modelo sólido personalizado obtenido mediante impresión 3D a la educación del paciente, comprobándose que la percepción visual y táctil del modelo permite a los pacientes entender mucho mejor su enfermedad y el tratamiento indicado para ella, mejorando la percepción de calidad del servicio prestado en las clínicas oftalmológicas.[ENG] This doctoral dissertation has been presented in the form of thesis by publication. The most important refractive surface of the human eye is the cornea, which has a hemispherical-shaped structure located in the anterior ocular segment. This structure, even in a non-pathological scenario, is not perfect, since it presents asymmetries that cause deformations, misalignments and decenterings between the two eyes of the same individual. When there are also corneal pathologies, such as ectasias, this asymmetry, and therefore its effects, are accentuated, causing in the patient a certainly significant deterioration of the visual capacity, something that shows the importance of having systems that allow precise corneal characterization to facilitate the detection, diagnosis and classification of ectasias. In this doctoral thesis, an integrated system capable of efficiently detecting (preclinical phase) and diagnosing (clinical phase), from an optical-geometric point of view, the progression of corneal ectasia, has been proposed, thus allowing a direct impact on the decision-making process concerning the visual quality of patients. To do so, and starting from a solid model customized in 3D generated with tools of Computer Assisted Design, several macroscopic morphogeometrical parameters of linear, superficial, volumetric and angular type have been proposed, with the aim of characterizing the progression of the most important corneal ectasia, the so-called keratoconus. The microscopic structure has also been studied, having programmed an application that allows to quantify the polymegatism and pleomorphism of the endothelial corneal cells. Subsequently, several univariate and multivariate diagnostic and classification systems for keratoconus have been revised, and it has been proven that morphogeometrical parameters allow both the detection and classification of keratoconus, basing on its degree of severity according to the RETICS, Amsler-Krumeich and Alió-Shabayek scales. In addition, two classification predictive models (demographical-optical-geometrical) of the disease degree based on the RETICS scale have been proposed, resulting in the development of two computer applications called EMKLAS and KERATOSCORE, which show the inherent difficulty of detecting this disease in its preclinical phase. Finally, a 3D printed personalized solid model has been applied to patient’s education, showing that the visual and tactile perception of the model allows patients to better understand their illness and the treatment indicated for it, improving the perception of quality of service provided in ophthalmological clinics.Las investigaciones que componen esta tesis doctoral se han llevado a cabo con el apoyo de la Red Temática para la Investigación Cooperativa en Salud (RETICS), referencia RD16/0008/0012, y han sido financiadas por el Instituto de Salud Calos III – Subdirección General de Redes y Centros de Investigación Cooperativa (Plan Nacional de I+D+I 2013-2016), el Fondo Europeo de Desarrollo Regional (FEDER), y el programa de Valorización de Resultados de la Universidad Politécnica de Cartagena (PROVALOR-UPCT).Esta tesis doctoral se presenta bajo la modalidad de compendio de publicaciones. Está formada por un total de doce documentos, todos ellos previamente publicados o aceptados para publicación. En concreto, 9 corresponden a artículos en revistas listadas en el ISI-JCR del Sciences Citation Index, mientras que los 3 restantes corresponden a capítulos de libro de la editorial Springer (Ranking Scholarly Publishers Indicators 4/200). Dichos documentos se enumeran a continuación de acuerdo con el orden cronológico en que han sido publicados durante el desarrollo de la investigación: 1. Cavas-Martínez F, Fernández-Pacheco DG, Cañavate FJF, Velázquez-Blázquez JS, Bolarín JM, Alió JL. Study of Morpho-Geometric Variables to Improve the Diagnosis in Keratoconus with Mild Visual Limitation. Symmetry. 2018;10(8):306. DOI: 10.3390/sym10080306. 2. Cavas-Martinez F, Fernandez-Pacheco DG, Canavate FJF, Velázquez-Blázquez JS, Bolarín J, Tiveron M, Alió J. Early keratoconus detection by patient-specific 3D modelling and geometric parameters analysis. Dyna. 2019. 94(2). DOI: 10.6036/8895. 3. Velázquez-Blázquez JS, Cavas-Martínez F, Alió del Barrio J, Fernandez-Pacheco DG, Cañavate FJF, Parras-Burgos D, Alió J. Detection of Subclinical Keratoconus Using Biometric Parameters. In: Rojas I., Valenzuela O., Rojas F., Ortuño F. (eds) Bioinformatics and Biomedical Engineering. IWBBIO 2019. Lecture Notes in Computer Science, vol 11466. Springer, Cham. DOI: 10.1007/978-3-030-17935-9_44. 4. Velázquez JS, Cavas F, Alió Del Barrio J, Fernández-Pacheco DG, Alió J. Assessment of the Association between In Vivo Corneal Morphogeometrical Changes and Keratoconus Eyes with Severe Visual Limitation. J Ophthalmol. 2019;2019:8731626-8731626. DOI: 10.1155/2019/8731626. 5. Velázquez-Blázquez JS, Cavas-Martínez F, Campuzano VA, Alió del Barrio J, Cañavate FJF, Alió J. Automatic image processing applied to corneal endothelium cell count and shape characterization. Dyna. 2020;95(2). DOI: 10.6036/9275. 6. Velázquez-Blázquez JS, Fernández-Pacheco DG, Alió del Barrio J, Alió JL, Cavas-Martínez F. Efficacy of Morpho-Geometrical Analysis of the Corneal Surfaces in Keratoconus Disease According to Moderate Visual Limitation. In: Cavas-Martínez F., Sanz-Adan F., Morer Camo P., Lostado Lorza R., Santamaría Peña J. (eds) Advances in Design Engineering. INGEGRAF 2019. Lecture Notes in Mechanical Engineering. Springer, Cham. 10.1007/978-3-030-41200-5_29. 7. Velázquez JS, Cavas F, Bolarín JM, Alió JL. 3D Printed Personalized Corneal Models as a Tool for Improving Patient’s Knowledge of an Asymmetric Disease. Symmetry. 2020;12(1):151. 10.3390/sym12010151. 8. Bolarín JM, Cavas F, Velázquez JS, Alió JL. A Machine-Learning Model Based on Morphogeometric Parameters for RETICS Disease Classification and GUI Development. Applied Sciences. 2020;10(5):1874. 10.3390/app10051874. 9. Velázquez JS, Cavas F, Bolarín JM, Alió JL. Comparison of Corneal Morphologic Parameters and High Order Aberrations in Keratoconus and Normal eyes. In: Rojas I., Valenzuela O., Rojas F., Ortuño F. (eds) Bioinformatics and Biomedical Engineering. IWBBIO 2020. Lecture Notes in Computer Science, vol 12108. Springer, Cham. DOI: 10.1007/978-3-030-45385-5_8. 10. Toprak I, Cavas F, Velázquez JS, Alió del Barrio JL, Alió JL. Subclinical keratoconus detection with three-dimensional (3-D) morphogeometric and volumetric analysis. Acta Ophthalmologica. (in press). 10.1111/aos.14433. 11. Velázquez JS, Cavas F, Piñero DP, Cañavate FJF, Alió del Barrio J, Alió JL. Morphogeometric analysis for characterization of keratoconus considering the spatial localization and projection of apex and minimum corneal thickness point. Journal of Advanced Research. (in press). DOI: 10.1016/j.jare.2020.03.012. 12. Velázquez-Blázquez JS, Bolarín JM, Cavas-Martínez F, Alió JL. EMKLAS: A New Automatic-Scoring System for Early and Mild Keratoconus Detection. Translational Vision Science & Technology. (in press). (2020).Escuela Internacional de Doctorado de la Universidad Politécnica de CartagenaUniversidad Politécnica de CartagenaPrograma de Doctorado en Tecnologías Industriale

Morphogeometric analysis for characterization of keratoconus considering the spatial localization and projection of apex and minimum corneal thickness point

This work evaluates changes in new morphogeometric indices developed considering the position of anterior and posterior corneal apex and minimum corneal thickness (MCT) point in keratoconus. This prospective comparative study included 440 eyes of 440 patients (age, 7–99 years): control (124 eyes) and keratoconus (KC) groups (316 eyes). Tomographic information (Sirius®, Costruzione Strumenti Oftalmici, Italy) was treated with SolidWorks v2013, creating the following morphogeometric parameters: geometric axis–apex line angle (GA–AP), geometric axis–MCT line angle (GA–MCT, apex line–MCT line angle (AP–MCT), and distances between apex and MCT points on the anterior (anterior AP–MCTd) and posterior corneal surface (posterior AP–MCTd). Statistically significant higher values of GA–AP, GA–MCT, AP–MCT and anterior AP–MCTd were found in the keratoconus group (p ≤ 0.001). Moderate significant correlations of corneal aberrations (r ≥ 0.587, p < 0.001) and corneal thickness parameters (r ≤ −0.414, p < 0.001) with GA–AP and AP–MCT were found. Anterior asphericity was found to be significantly correlated with anterior and posterior AP–MCTd (r ≥ 0.430, p < 0.001). Likewise, GA–AP and AP–MCT showed a good diagnostic ability for the detection of keratoconus, with optimal cutoff values of 9.61° (sensitivity 85.5%, specificity 80.3%) and 18.08° (sensitivity 80.5%, specificity 78.7%), respectively. These new morphogeometric indices allow a clinical characterization of the 3-D structural alteration occurring in keratoconus, with less coincidence in the spatial projection of the apex and MCT points of both corneal surfaces. Future studies should confirm the potential impact on the precision of these indices of the variability of posterior corneal surface measurements obtained with Scheimpflug imaging technology.This publication has been carried out in the framework of the Thematic Network for Co-Operative Research in Health (RETICS), reference number RD16/0008/0012, financed by the Carlos III Health Institute–General Subdirection of Networks and Cooperative Investigation Centers (R&D&I National Plan 2013–2016) and the European Regional Development Fund (FEDER). The author David P. Piñero has been supported by the Ministry of Economy, Industry and Competitiveness of Spain within the program Ramón y Cajal, RYC-2016-20471

Coupled Biomechanical Response of the Cornea Assessed by Non-Contact Tonometry. A Simulation Study

The mechanical response of the cornea subjected to a non-contact air-jet tonometry diagnostic test represents an interplay between its geometry, the corneal material behavior and the loading. The objective is to study this interplay to better understand and interpret the results obtained with a non-contact tonometry test. A patient-specific finite element model of a healthy eye, accounting for the load free configuration, was used. The corneal tissue was modeled as an anisotropic hyperelastic material with two preferential directions. Three different sets of parameters within the human experimental range obtained from inflation tests were considered. The influence of the IOP was studied by considering four pressure levels (10–28 mmHg) whereas the influence of corneal thickness was studied by inducing a uniform variation (300–600 microns). A Computer Fluid Dynamics (CFD) air-jet simulation determined pressure loading exerted on the anterior corneal surface. The maximum apex displacement showed a linear variation with IOP for all materials examined. On the contrary, the maximum apex displacement followed a cubic relation with corneal thickness. In addition, a significant sensitivity of the apical displacement to the corneal stiffness was also obtained. Explanation to this behavior was found in the fact that the cornea experiences bending when subjected to an air-puff loading, causing the anterior surface to work in compression whereas the posterior surface works in tension. Hence, collagen fibers located at the anterior surface do not contribute to load bearing. Non-contact tonometry devices give useful information that could be misleading since the corneal deformation is the result of the interaction between the mechanical properties, IOP, and geometry. Therefore, a non-contact tonometry test is not sufficient to evaluate their individual contribution and a complete in-vivo characterization would require more than one test to independently determine the membrane and bending corneal behavior.The research leading these results has received funding from the European Union’s Seven Framework Program managed by REA Research Executive agency http://ec.europa.eu/research/rea (FP7/2007-2013) under Grant Agreement n° FP7-SME-2013 606634 and the Spanish Ministry of Economy and Competitiveness (DPI2011-27939-C02-01)

Computational planning tools in ophthalmology: Intrastromal corneal ring surgery

This thesis addresses the problem of the simulation of intrastromal corneal ring segment surgery for the reduction of myopia and astigmatism, as well as the stabilisation of keratoconus (KC). This disease causes high myopia, irregular astigmatism and reduction of the patient's visual acuity to the point of blindness. Therefore there are several techniques to try to stabilise it and, thus, prevent its progression. For mild keratoconus, it is enough to use special spectacles or lenses to try to correct it, but in more advanced cases it would be necessary to use refractive surgery to try to stop the progression of the disease. The most common ones to avoid the cornea transplant (PK) are the cross-linking and the additive surgery of intrastromal rings. The current planning tools are empirical, based on the nomograms of the ring manufactures, and rely on the experience of the surgeon. Unfortunately, deterministic tools able to estimate the postsurgical visual results of this treatment do not exist. Therefore, the aim of the current thesis is to establish a realistic numerical framework to simulate intrastromal ring surgeries and estimate the mechanical and optical postsurgical outcomes. There are different types of rings depending on their angle and cross-section. There are two large groups of rings: segments which have an angle of less than 360º and those that cover the entire circumference. In the first group we find rings of triangular section such as the Keraring (Mediaphacos, BeloHorizonte, Brazil) and the Ferrara (AJL Ophthalmic Ltd, Spain) and rings of hexagonal section like the Intacs (Additional Technology Inc.). In the second group we can find the MyoRing (Dioptex, GmbH.) whose cross-section is the combination of a parabola and a circumference and the Intacs SK whose section is oval. Due to the complexity of the simulation, since multiple variables are involved, such as the type of rings, the model of the corneal material, the contact conditions between them, etc., two methodologies arised which simulated the insertion of the rings. Both are based on generating a hole in the corneal stroma, introducing the ring and closing the hole with the ring inside, establishing contact until the simulation is completed. In the first of the methodologies the hole was generated by introducing a pressure, while the second was used to an auxiliary tool, such as balloon angioplasty to introduce endovascular stents, which is displaced generating enough hole to insert the rings. As with all numerical simulations, they were not exempt of limitations, although with the first of the methodologies only circular cross--section rings were simulated and in some configurations, there was pressure inside the hole, so it was decided to focus on the second. Nevertheless, interesting conclusions were obtained: the greatest correction was obtained by placing the rings with the largest section near the apex, and whether the ring is located near the epithelium, the stresses generated in the stroma can cause the ring to extrude. With the second methodology based on a displacement control, it was possible to simulate most of the cross-sections and very interesting studies were carried out that gave conclusive results. The most important were: i) the most influential parameter is the depth of insertion; ii) considering the physiological depth of the surgery, the greater optical change is provided by the diameter of the ring, and the fine adjusted is reached with the size of the implant cross--section, i.e the diameter of the implant and the size of the cross--section are the key on regulating the refractive correction; iii) the friction between ring and stroma is important to consider it because a prediction of 2 or 3 diopters could be lost; iv) whether the KC progression is stress-driven, only MyoRing can stop its progression; v) when the covered arc of the segments is more than 320º, axisymmetric model could be used instead of tridimensional model, saving computational time; vi) the anisotropy of the model does not play an important role because the rings are much stiffer than corneal tissue; vii) the implants cannot consider such as second limbus since they act as a dynamic pivot that moves along the circadian cycles of intraocular pressure (IOP); viii) preliminary nomograms is built which allow the estimation of the optical outputs according to the size and typology of the ring and optical zone of implantation.Additionally, a characterisation of ring material was carried out by means two complementary methods: uncertainty analysis and iFEM optimisation, concluding that the manufacturing process of the rings could be the cause of the alteration of the material between the raw PMMA and the ring already prepared for its insertion.<br /