Impacto da ortoqueratologia e da cirurgia refractiva lasik na topografia da córnea, na refracção central e periférica e na qualidade visual do olho

Abstract

The present Thesis integrates the results of the transversal e longitudinal studies, conducted during a 3 year period, at the Clinical & Experimental Optometry Research Lab – Minho University (CEORLab) and in Ophtalmologic Clinic Novovision (Madrid, Spain), as it is shown on Appendix 1. Optical and surgical solutions to correct myopia still have some limitations when it comes to independency of visual correction, as it was assessed in this study with a survey which evaluated the quality of life of patients. The patients, either in Laser-Assisted in Situ Keratomileusis (LASIK) and orthokeratology or Corneal Refractive Therapy (CRT), describe symptoms in terms of glare that are related to changes induced in the anterior corneal surface to correct or compensate myopia. Studies were conducted to verify the changes of anterior corneal surface induced by orthokeratology, Standard LASIK and Customized LASIK, by examining the topography of the anterior corneal surface (refractive power). Using this information higher-order aberrations were also analyzed, and these allowed us to understand the symptoms of the patients in these types of treatments. Were found increments of refractive power in the paracentral zones, which are on the basis of changes in terms of aberrations, particularly spherical aberration and coma aberration. These changes were more evident on CRT treatment than in LASIK, due to smaller treatment area and to the anatomical changes inherent to each of the treatments with increase of thickness in the paracentral area in CRT instead of central ablation in LASIK. Both interventions, surgical and non-surgical, have shown an increase located in the paracentral corneal anterior surface. However, the smaller optical zone and higher curvature of the paracentral region with orthokeratology treatment seems to have the ability to create a more effective relative myopic effect on the power of the peripheral cornea, higher than in the LASIK treatment, which may have implications in reducing the progression of myopia. In this Thesis it is shown that for the CRT treatment, more myopic values can be induced in the periphery of the retina (from 25º of each visual field) compared to baseline values before treatment. This effect was not observed in LASIK treatment, where all values are less myopic than baseline. Despite the presence of relative peripheral myopic refractive error in the periphery after both treatments, CRT provides a greater effect for a given myopic correction. CRT and LASIK induce changes in the power of the anterior corneal surface to correct myopia, leading to a significant change in both its topographic pattern and peripheral refractive profile. Orthokeratology has more potential in inducing peripheral myopization at the expense of a poorer optical quality.