No / The EyeSys videokeratoscope (VK) measurements of the principal corneal meridians of 98 subjects already analysed by Douthwaite et al. [Ophthal. Physiol. Opt. (1999)19:467¿474] were re-analysed in order to revise the assessment of asphericity, to derive information on corneal tilt and to assess the degree to which the corneal section approximates to that of a conic section. The range of normality for the revised p-value (asphericity) was from 0.57 to 0.97 for the near horizontal and from 0.56 to 1.08 in the near vertical principal meridians. The approximate corneal tilt angles ranged from ¿3.95 to +8.13 degrees in the horizontal and from ¿8.99 to +9.33 degrees in the vertical meridian. A tilted conicoidal surface will display a linear relationship (r = 1) when a scatterplot is drawn of the perpendicular distance squared vs radius squared, after first averaging the two semimeridian results for each VK ring. Analysing the results from the human cornea in the same way allows an assessment of the degree to which the corneal section approximates to that of the conic section.

This work aims to improve the predictability of asphericity and average keratometry in keratoconus patients after implantation of intrastromal corneal ring segments (ICRS) by creating computational models based on machine learning, using tomographic data of the cornea. This study included 209 eyes of 160 keratoconus (grades I, II and III) implanted with ICRS. The Ferrara ICRS with 160 degrees of arch was implanted in all patients. The ICRS thickness varied from 150 to 250 micra. One or two segments were implanted. The base was composed of corneal tomography Pentacam® (Oculus, Wetzlar, Alemanha) parameters, clinical data and Ferrara ring data totaling 39 parameters. To create the models, neural network algorithms type multlayer perceptron (MLP) and linear regression were used. This study was conducted in four phases: (1) Preparation of the database and setting the values to be predicted mean keratometry and asphericity; (2) Calculation of the variation mean keratometry and asphericity and the nomogram calculation error; (3) Application of machine learning algorithms and attribute selection; (4) Mean keratometry and asphericity variation calculation provided for comparing algorithm with the variation of the preoperative and postoperative calculation of the algorithm and of the error. As a result, the best mean absolute error value found for asphericity was 0.19 and mean keratometry was 1.18. Comparing the mean absolute error values of the nomogram and the average absolute error of the algorithm, there was an improvement of 0.11 to asphericity and 0.09 to mean keratometry in relation to the current nomogram, confirming that the use of computational models can achieve more accurate results may contribute to surgical decision in an attempt to improve the quality of vision of keratoconus patients. / O presente trabalho destina-se a melhorar a previsibilidade da asfericidade e da ceratometria média no pós-operatório de implante de anel intraestromal (SAIC) em pacientes com ceratocone por meio da criação de modelos computacionais baseados em aprendizagem de máquina, utilizando dados tomográficos da córnea. Foram incluídos 209 olhos de 160 pacientes com graus I, II e III de ceratocone submetidos a cirurgia com implante de SAIC. Em todos os pacientes foi implantado anel de Ferrara com 160o de arco com variação de espessura entre 150 e 250 µm e presença de 1 ou 2 segmentos. A base foi composta por parâmetros da tomografia de córnea pentacam®, dados clínicos e dados do anel de Ferrara totalizando 39 parâmetros. Para criação dos modelos, foram utilizados os algoritmos Rede Neural do tipo multlayer perceptron (MLP) e regressão linear. Este estudo foi desenvolvido em 4 fases distintas: (1) Preparação da base de dados e definição dos valores a serem preditos de ceratometria média e asfericidade; (2) Cálculo da variação da ceratometria média e asfericidade e cálculo do erro do nomograma; (3) Aplicação dos algoritmos de aprendizagem de máquina e seleção de atributos; (4) Cálculo da variação da ceratometria média e da asfericidade prevista pelo algoritmo comparando com a variação do pré e pós operatório e cálculo do erro do algoritmo. Como resultado, o melhor valor do erro absoluto médio encontrado para asfericidade foi 0.19 e para ceratometria média foi 1.18. Comparando os valores do erro médio do nomograma e o erro médio do algoritmo, houve uma melhora de 0.11 para asfericidade e 0.09 para ceratometria média em relação ao nomograma atual, confirmando que a utilização de modelos computacionais é capaz de alcançar resultados mais precisos podendo contribuir para decisão cirúrgica na tentativa de melhorar a qualidade de visão de pacientes com ceratocone.

L’amélioration des matériaux et des technologies de lentilles de contact a permis le recours de plus en plus fréquent à un type de lentille de contact à grand diamètre reposant sur la sclère : la lentille sclérale (SL). Celle-ci est majoritairement utilisée pour la réadaptation visuelle de patient vivant avec divers types de déformations cornéennes, mais également pour le traitement de maladie de surface oculaire et la correction optique de la simple erreur de réfraction lorsque les autres modalités de lentilles ne peuvent être tolérées. Ce mémoire a pour objectif d’évaluer l’influence de l’asphéricité des surfaces antérieure (ASA) et postérieure (ASP) sur la performance visuelle d’un porteur de SL chez deux groupes distincts : une cohorte de 12 participants sans anomalie cornéenne et une cohorte de 9 participants ayant un diagnostic de kératocône (KC). Lors de l’expérience, quatre différentes SL ayant différents profils d’asphéricité ont été étudiées sur l’œil droit seulement. Pour chaque SL, les mesures d’acuité visuelle à haut contraste (AVHC), l’acuité visuelle à bas contraste (AVHC) et les valeurs moyennes quadratiques (root-mean-square ou RMS) des différents coefficients d’aberrations d’ordres supérieurs (AOS) ont été compilées pour chacun de ces designs aux diamètres pupillaires 3, 4, 5 et 6 mm. Les résultats obtenus suggèrent que l’augmentation de l’ASA d’une SL portée à l’œil droit génère une augmentation de l’aberration sphérique négative, de la coma verticale et horizontale négative chez les deux groupes. L’augmentation de l’ASA entraîne toutefois une augmentation de l’AOS totale et du trèfle total chez les participants sans anomalie cornéenne. Chez le groupe de participants atteint de KC, l’augmentation de l’ASA entraîne une diminution non significative des AOS totales et une augmentation non significative de l’aberration trèfle total. Bien que des études supplémentaires soient nécessaires pour bien comprendre l’influence de l’asphéricité sur les AOS chez les participants atteints de KC, la manipulation de celle-ci permettrait de réduire l’amplitude de certains types d’AOS dans certains cas particuliers. / Improvements in materials and technology have led to the increased use of a large diameter contact lens that rests on the sclera: the scleral lens (SL). These lenses are mainly used for visual rehabilitation of patients with various types of corneal ectasia, for the treatment of ocular surface disease and also for the optical correction of simple refractive error when other lens modalities are not tolerated. The purpose of this dissertation is to evaluate the influence of anterior surface asphericity (ASA) and posterior surface asphericity (ASP) on the visual performance of a SL wearer in two distinct groups: a cohort of 12 participants with no corneal abnormalities and a cohort of 9 participants with a diagnosis of keratoconus (KC). Four different SLs with different aspheric profiles were studied on the right eye only. For each SL, high-contrast visual acuity (HCVA), low contrast visual acuity (LCVA) measurements were measured. The root-mean-square (RMS) values of the higher-order aberration (HOA) Zernike coefficients were also measured for each of these designs for a pupil diameter of 3, 4, 5 and 6 mm. The results of this study suggest that increasing the anterior asphericity of a SL worn on the right eye generates an increase in negative spherical aberration, negative vertical and horizontal coma in both groups. Increasing anterior asphericity leads to an increase in total HOA and total trefoil in participants without corneal anomalies. In the group of participants with KC, increasing asphericity results in a non-significant decrease in total HOA and a non-significant increase in total trefoil aberration. Although additional studies are needed to understand the influence of asphericity on HOA in participants with KC, the manipulation of the anterior asphericity could reduce the amplitude of some types of HOA in some cases.