Laurent Bataille

Cornea and Ocular Surface Treatment

In addition to being a protective shield, the cornea represents two thirds of the eyes refractive power. Corneal pathology can affect one or all of the corneal layers, producing corneal opacity. Although full corneal thickness keratoplasty has been the standard procedure, the ideal strategy would be to replace only the damaged layer. Current difficulties in corneal transplantation, mainly immune rejection and shortage of organ supply, place more emphasis on the development of artificial corneas. Bioengineered corneas range from prosthetic devices that solely address the replacement of the corneal function, to tissue-engineered hydrogels that allow regeneration of the tissue. Recently, major advances in the biology of corneal stem cells have been achieved. However, the therapeutic use of these stem cell types has the disadvantage of needing an intact stem cell compartment, which is usually damaged. In addition, long ex vivo culture is needed to generate enough cell numbers for transplantation. In the near future, combination of advanced biomaterials with cells from abundant outer sources will allow advances in the field. For the former, magnetically aligned collagen is one of the most promising ones. For the latter, different cell types will be optimal: 1) for epithelial replacement: oral mucosal epithelium, ear epidermis, or bone marrow- mesenchymal stem cells, 2) for stromal regeneration: adipose-derived stem cells and 3) for endothelial replacement, the possibility of in vitro directed differentiation of adipose-derived stem cells towards endothelial cells provides an exciting new approach.

Biointegration of corneal macroporous membranes based on poly(ethyl acrylate) copolymers in an experimental animal model.

Currently available keratoprosthesis models (nonbiological corneal substitutes) have a less than 75% graft survival rate at 2 years. We aimed at developing a model for keratoprosthesis based on the use of poly(ethyl acrylate) (PEA)-based copolymers, extracellular matrix-protein coating and colonization with adipose-derived mesenchymal stem cells. Human adipose tissue derived mesenchymal stem cells (h-ADASC) colonization efficiency of seven PEA-based copolymers in combination with four extracellular matrix coatings were evaluated in vitro. Then, macroporous membranes composed of the optimal PEA subtypes and coating proteins were implanted inside rabbit cornea. After a 3-month follow-up, the animals were euthanized, and the clinical and histological biointegration of the implanted material were assessed. h-ADASC adhered and survived when cultured in all PEA-based macroporous membranes. The addition of high hydrophilicity to PEA membranes decreased h-ADASC colonization in vitro. PEA-based copolymer containing 10% hydroxyethyl acrylate (PEA-HEA10) or 10% acrylic acid (PEA-AAc10) monomeric units showed the best cellular colonization rates. Collagen plus keratan sulfate-coated polymers demonstrated enhanced cellular colonization respect to fibronectin, collagen, or uncoated PEAs. In vivo implantation of membranes resulted in an extrusion rate of 72% for PEA, 50% for PEA-AAc10, but remarkably of 0% for PEA-HEA10. h-ADASC survival was demonstrated in all the membranes after 3 months follow-up. A slight reduction in the extrusion rate of h-ADASC colonized materials was observed. No significant differences between the groups with and without h-ADASC were detected respect to transparency or neovascularization. We propose PEA with low hydroxylation as a scaffold for the anchoring ring of future keratoprosthesis.

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.

Biocompatibility and Biomechanical Effect of Single Wall Carbon Nanotubes Implanted in the Corneal Stroma: A Proof of Concept Investigation

Corneal ectatic disorders are characterized by a progressive weakening of the tissue due to biomechanical alterations of the corneal collagen fibers. Carbon nanostructures, mainly carbon nanotubes (CNTs) and graphene, are nanomaterials that offer extraordinary mechanical properties and are used to increase the rigidity of different materials and biomolecules such as collagen fibers. We conducted an experimental investigation where New Zealand rabbits were treated with a composition of CNTs suspended in balanced saline solution which was applied in the corneal tissue. Biocompatibility of the composition was assessed by means of histopathology analysis and mechanical properties by stress-strain measurements. Histopathology samples stained with blue Alcian showed that there were no fibrous scaring and no alterations in the mucopolysaccharides of the stroma. It also showed that there were no signs of active inflammation. These were confirmed when Masson trichrome staining was performed. Biomechanical evaluation assessed by means of tensile test showed that there is a trend to obtain higher levels of rigidity in those corneas implanted with CNTs, although these changes are not statistically significant (p > 0.05). Implanting CNTs is biocompatible and safe procedure for the corneal stroma which can lead to an increase in the rigidity of the collagen fibers.

Optimizing Genipin Concentration for Corneal Collagen Cross-Linking: An ex vivo Study

Purpose: Studying genipin variable concentrations, treatment durations, and delivery methods as a substance to increase corneal stiffness by inducing corneal collagen cross-linking (CXL). Materials and Methods: 100 bovine corneas treated with different genipin concentrations (0.1, 0.5, and 1%) and treatment durations (15 min, 40 min, 2 h, and 3 days) through different delivery methods compared to 10 controls treated with riboflavin/UV. Histology examination, enzymatic digestion with collagenase and thermal differential scanning calorimetry were performed on the different samples. Results: Bovine corneas soaked in 0.5% genipin morphologically showed 4.7% CXL in comparison to 5.6% in controls (p < 0.05). Corneas treated with topical 0.5% genipin, by a 140-µL drop applied hourly for 2 h, showed 7% corneal CXL. Corneas treated with topical genipin 0.5% for 30 min, 1 and 2 h showed 54 ± 6, 40 ± 7, and 39 ± 9% enzymatic degradation, respectively, in comparison to controls (74%). Corneas treated with 0.5% genipin for 1, 2, and 8 h showed higher thermal denaturation resistance (Td values of 64.9 ± 0.3, 64.7 ± 0.0 and 67.3 ± 0.9), respectively, in comparison to the control group (64.6 ± 0.5) (p < 0.05). Conclusions: Genipin 0.5%, in a 140-µL drop applied hourly for 2 h, showed better potential to enhance corneal stiffness and stability through inducing CXL.

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.