Caracterització dels paràmetres corneals per a l'adaptació de lents de contacte en casos de queratocon
- Autores: Enric Mas
- Directores de la Tesis: Joan Gispets (dir. tes.), Nuria Lupón (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2019
- Idioma: español
- Tribunal Calificador de la Tesis: César Villa Collar (presid.), Meritxell Vilaseca Ricart (secret.), José Lamarca Mateu (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería Óptica por la Universidad Politécnica de Catalunya
- Materias:
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- Resumen
Introduction The characterization of the corneal surface and the classification of keratoconus into diverse severity stages is a field of research in constant evolution, not only because of technology advances, but also with the definition of new parameters that allow a better understanding of the geometry, status and evolution of affected eyes, as compared with healthy eyes. Within the evolution of our knowledge about keratoconus, it is increasingly relevant to analyze the changes caused by this pathology to the morphology of the peripheral cornea with the purpose of successfully developing large diameter corneal contact lenses (CL) for these patients, to improve visual quality and comfort, with minimum interference with ocular physiology.
Current Investigations The objective of this series of studies was to improve our knowledge of corneal geometry as a whole and, in particular, to determine if corneal changes occurring in keratoconus are mainly corneal, limbal / scleral, or a combination of both. This information is key to design and fit large diameter corneal CL in patients with different stages of the condition, as a complementary or alternative solution to current fitting strategies.
With this purpose in mind, Scheimpflug images at different corneal meridians were used to analyse several corneal and anterior segment parameters of eyes of patients with keratoconus at different stages of the condition. As such, one of the novel aspects of the present study consisted in a complete analysis of the anterior segment, not limited to parameters provided by the software of the Pentacam HR®, but also defining new parameters, not available in the current version of the software. These parameters, manually measured on Scheimpflug images, included a newly defined parameter (DL, or distance to the lens, distance from the end point of the corneal sagittal line to the anterior surface of the lens) which proved very useful for the required corneal-limbal characterization.
The following step was to analyse the corneal periphery by measuring the corresponding peripheral corneal angles (at a chord length between 8.6 and 12.6 mm) and the degree of peripheral revolution symmetry (defined as the difference between the smallest and largest peripheral corneal angle for a particular eye). This was accomplished with a newly developed methodology, as the areas under study had not been previously explored with Scheimpflug images.
Finally, a new design for a large diameter corneal CL was developed for keratoconus and a new mathematical model was implemented to calculate the parameters of these CLs from the previously obtained Scheimpflug images measurements. In order to conduct a practical validation of the viability of this new CL design and mathematical methodology in keratoconus, a preliminary clinical study on 20 eyes (10 patients) with different stages of the condition was conducted.
Conclusions Keratoconus was found to be associated with an increase in anterior chamber depth which, in turn, leads to increased values both in corneal internal sagittal length (as measured from the endothelium) and in the DL distance. Indeed, the increase in DL may be evidence of an anterior displacement of the corneal-limbal transition zone of the eye, with reference to the plane of the iris. Therefore, changes occurring in keratoconus would not only affect the cornea, but the whole of the anterior segment of the eye, including the limbal structures.
A significant increase in corneal peripheral angle in the early stages of keratoconus that does not seem to progress in later stages of the condition was observed.
The degree of peripheral revolution symmetry was not found to differ between healthy and keratoconus eyes. Therefore, CL with peripheral support and symmetry of revolution in this area may be fitted as successfully in keratoconus as in healthy eyes.
