Francisco J. F. Cañavate

Geometrical Custom Modeling of Human Cornea In Vivo and Its Use for the Diagnosis of Corneal Ectasia

Aim To establish a new procedure for 3D geometric reconstruction of the human cornea to obtain a solid model that represents a personalized and in vivo morphology of both the anterior and posterior corneal surfaces. This model is later analyzed to obtain geometric variables enabling the characterization of the corneal geometry and establishing a new clinical diagnostic criterion in order to distinguish between healthy corneas and corneas with keratoconus. Method The method for the geometric reconstruction of the cornea consists of the following steps: capture and preprocessing of the spatial point clouds provided by the Sirius topographer that represent both anterior and posterior corneal surfaces, reconstruction of the corneal geometric surfaces and generation of the solid model. Later, geometric variables are extracted from the model obtained and statistically analyzed to detect deformations of the cornea. Results The variables that achieved the best results in the diagnosis of keratoconus were anterior corneal surface area (ROC area: 0.847, p<0.000, std. error: 0.038, 95% CI: 0.777 to 0.925), posterior corneal surface area (ROC area: 0.807, p<0.000, std. error: 0.042, 95% CI: 0,726 to 0,889), anterior apex deviation (ROC area: 0.735, p<0.000, std. error: 0.053, 95% CI: 0.630 to 0.840) and posterior apex deviation (ROC area: 0.891, p<0.000, std. error: 0.039, 95% CI: 0.8146 to 0.9672). Conclusion Geometric modeling enables accurate characterization of the human cornea. Also, from a clinical point of view, the procedure described has established a new approach for the study of eye-related diseases.

A new approach to keratoconus detection based on corneal morphogeometric analysis

Purpose To characterize corneal structural changes in keratoconus using a new morphogeometric approach and to evaluate its potential diagnostic ability. Methods Comparative study including 464 eyes of 464 patients (age, 16 and 72 years) divided into two groups: control group (143 healthy eyes) and keratoconus group (321 keratoconus eyes). Topographic information (Sirius, CSO, Italy) was processed with SolidWorks v2012 and a solid model representing the geometry of each cornea was generated. The following parameters were defined: anterior (Aant) and posterior (Apost) corneal surface areas, area of the cornea within the sagittal plane passing through the Z axis and the apex (Aapexant, Aapexpost) and minimum thickness points (Amctant, Amctpost) of the anterior and posterior corneal surfaces, and average distance from the Z axis to the apex (Dapexant, Dapexpost) and minimum thickness points (Dmctant, Dmctpost) of both corneal surfaces. Results Significant differences among control and keratoconus group were found in Aapexant, Aapexpost, Amctant, Amctpost, Dapexant, Dapexpost (all p<0.001), Apost (p = 0.014), and Dmctpost (p = 0.035). Significant correlations in keratoconus group were found between Aant and Apost (r = 0.836), Amctant and Amctpost (r = 0.983), and Dmctant and Dmctpost (r = 0.954, all p<0.001). A logistic regression analysis revealed that the detection of keratoconus grade I (Amsler Krumeich) was related to Apost, Atot, Aapexant, Amctant, Amctpost, Dapexpost, Dmctant and Dmctpost (Hosmer-Lemeshow: p>0.05, R2 Nagelkerke: 0.926). The overall percentage of cases correctly classified by the model was 97.30%. Conclusions Our morphogeometric approach based on the analysis of the cornea as a solid is useful for the characterization and detection of keratoconus.

A Study for Parametric Morphogeometric Operators to Assist the Detection of Keratoconus

The aim of this study is to describe a new keratoconus detection method based on the analysis of certain parametric morphogeometric operators extracted from a custom patient-specific three-dimensional (3D) model of the human cornea. A corneal geometric reconstruction is firstly performed using zonal functions and retrospective Scheimpflug tomography data from 107 eyes of 107 patients. The posterior corneal surface is later analysed using an optimised computational geometry technique and the morphology of healthy and keratoconic corneas is characterized by means of geometric variables. The performance of these variables as predictors of a new geometric marker is assessed through a receiver operating characteristic (ROC) curve analysis and their correlations are analysed through Pearson or Spearman coefficients. The posterior apex deviation variable shows the best keratoconus diagnosis capability. However, the strongest correlations in both healthy and pathological corneas are provided by the metrics directly related to the thickness as the sagittal plane area at the apex and the sagittal plane area at the minimum thickness point. A comparison of the screening of keratoconus provided by the Sirius topographer and the detection of corneal ectasia using the posterior apex deviation parameter is also performed, demonstrating the accuracy of this characterization as an effective marker of the diagnosis and ectatic disease progression.

Keratoconus Detection Based on a New Corneal Volumetric Analysis

There are numerous tomographic indices for the detection of keratoconus risk. When the indexes based on corneal volume are analyzed, two problems are presented: on the one hand, they are not very sensitive to the detection of incipient cases of keratoconus because they are not locally defined in the primary developmental region of the structural abnormalities; and on the other hand, they do not register the geometric decompensation driven by the asymmetry present during the disease progression. This work performed a morphogeometric modeling of the cornea by the aid of CAD tools and using raw topographic data (Sirius system, CSO, Firenze). For this method, four singular points present on the corneal surfaces were located and the following parameters based on corneal volume were calculated: VOLmct, defined by the points of minimal thickness; VOLaap, defined by the anterior corneal apex, and VOLpap, defined by the posterior corneal apex. The results demonstrate that a further reduction of corneal volume in keratoconus happens and significantly progresses along the disease severity level. The combination of optical and volumetric data, that collect the sensitivity of the asymmetry generated by the disease, allows an accurate detection of incipient cases and follow up of the disease progression.

MODELADO VIRTUAL DE UNA ESTRUCTURA BIOLOGICA: LA CORNEA HUMANA

ABSTRACT: The cornea is the most important part of the anterior segment of the human eye. In a natural scenario, the tissue that forms part of the corneal architecture presents a stable geometrical morphology, while in a pathological scenario a morphological alteration that affects to the geometry of its architecture is detected. The use of virtual models of biologic structures in the field of Biomedical Engineering has been demonstrated to be very useful in clinical practice for diagnosis and surgical reconstruction. This paper presents the virtual modelling of the human cornea as a technique for the diagnosis of the corneal pathology named keratoconus. After generating the virtual model of the cornea, several geometric variables are then extracted and analyzed, permitting to differentiate between healthy and keratoconic corneas. The obtained results have been clinically validated and demonstrate the functionality of the methodology applied, being possible to extend this methodology to other geometric variables. Keywords: geometric modelling, keratoconus, corneal disease, virtual model.

Reconstruction by Low Cost Software Based on Photogrammetry as a Reverse Engineering Process

Among the various types of scanning that can be found on the market to perform a three-dimensional reconstruction, an alternative is highlighted due to its low cost and its ease of use, making it suitable for a great amount of applications. This is Image-based 3D Modeling and Rendering (IB3DMR), in which it is possible to generate a three-dimensional model from a set of 2D photographs. Among the existing commercial applications based on the IB3DMR, this communication has selected the Autodesk ReCap software, which is free and provides great features in terms of simplicity of operation, automation of the reconstruction process and possibility of exporting to other more complex applications. The use of this type of technologies based on photogrammetry is an alternative to the conventional reverse engineering processes, so a study with seven different pieces in terms of colour, geometry and texture has been performed for its assessment, obtaining three-dimensional reconstructions with very satisfactory results.

Assessment of Pattern and Shape Symmetry of Bilateral Normal Corneas by Scheimpflug 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. Pinero has been supported by the Ministry of Economy, Industry and Competitiveness of Spain within the program Ramon y Cajal, RYC-2016-20471.

Study of Morpho-Geometric Variables to Improve the Diagnosis in Keratoconus with Mild Visual Limitation

The validation of new methods for the diagnosis of incipient cases of Keratoconus (KC) with mild visual limitation is of great interest in the field of ophthalmology. During the asymmetric progression of the disease, the current diagnostic indexes do not record the geometric decompensation of the corneal curvature nor the variation of the spatial profile that occurs in singular points of the cornea. The purpose of this work is to determine the structural characterization of the asymmetry of the disease by using morpho-geometric parameters in KC eyes with mild visual limitation including using an analysis of a patient-specific virtual model with the aid of computer-aided design (CAD) tools. This comparative study included 80 eyes of patients classified as mild KC according to the degree of visual limitation and a control group of 122 eyes of normal patients. The metric with the highest area under the receiver operating characteristic (ROC) curve was the posterior apex deviation. The most prominent correlation was found between the anterior and posterior deviations of the thinnest point for the mild keratoconic cases. This new custom computational approach provides the clinician with a three-dimensional view of the corneal architecture when the visual loss starts to impair.

Keratoconus Diagnosis by Patient-Specific 3D Modelling and Geometric Parameters Analysis

The aim of this study is to describe a new technique for diagnosing keratoconus based on Patient-specific 3D modelling. This procedure can diagnose small variations in the morphology of the cornea due to keratoconus disease. The posterior corneal surface was analysed using an optimised computational geometric procedure and raw data provided by a corneal tomographer. A retrospective observational case series study was carried out. A total of 86 eyes from 86 patients were obtained and divided into two groups: one group composed of 43 healthy eyes and the other of 43 eyes diagnosed with keratoconus. The predictive value of each morphogeometric variable was established through a receiver operating characteristic (ROC) analysis. The posterior apex deviation variable showed the best keratoconus diagnosis capability (area: 0.9165, p < 0.000, std. error: 0.035, 95% CI: 0.846-0.986), with a cut-off value of 0.097 mm and an associated sensitivity and specificity of 89% and 88%, respectively. Patient-specific geometric models of the cornea can provide accurate quantitative information about the morphogeometric properties of the cornea on several singular points of the posterior surface and describe changes in the corneal anatomy due to keratoconus disease. This accurate characterisation of the cornea enables new evaluation criteria in the diagnosis of this type of ectasia and demonstrates that a device-independent approach to the diagnosis of keratoconus is feasible.

Geometric Modelling of the Human Cornea: A New Approach for the Study of Corneal Ectatic Disease. A Pilot Investigation.

Purpose: 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.