Simulación de queratotomía arqueada por medio de un modelo de elementos finitos: aplicación de una plataforma de interacción entre Matlab y COMSOL Multiphysics / Simulation of arcuate keratotomy using the finite elements method: an application of an interaction platform of Matlab and COMSOL Multiphysics

La queratotomía radial es uno de los métodos quirúrgicos empleados para corregir los defectos ópticos de las personas; ésta ha sido ampliamente estudiada, e incluso se han propuesto nomogramas que permiten predecir los resultados de algunas geometrías; a pesar de esto, las experiencias postoperatorias han demostrado que la tasa de éxito de las cirugías es baja, ya que se presenta hipocorrección o hipercorrección de los pacientes, obligándolos a usar ayudas externas o llevándolos a someterse nuevamente a una cirugía. Teniendo en cuenta esto, se desarrolló una plataforma para simular estas cirugías por medio del método de elementos finitos, empleando los programas Matlab y COMSOL Multiphysics. Por medio de la rutina creada es posible obtener un modelo de la córnea preoperatoria que se asemeje tanto en geometría, como en condiciones de esfuerzo, a la córnea real; adicionalmente, es posible adaptar la geometría de la queratotomía radial que desee simularse. Se realizaron simulaciones para una cirugía compuesta de dos arcos y otra de tres arcos; los resultados obtenidos demuestran la capacidad de la simulación numérica para avanzar en el desarrollo de la cirugía refractiva, al ser posible estudiar parámetros, que de forma experimental, son difíciles de tener en cuenta, como la geometría inicial de la córnea y la edad del paciente, lo cual influye en el módulo de elasticidad del material; por otra parte, se encontró que esta aplicación es una potencial herramienta para los oftalmólogos, pues tiene la capacidad de predecir los resultados postoperatorios.

Radial keratotomy is used as a methodology to correct refractive errors. This surgery has been widely studied and also nomograms have been proposed in order to predict postoperative results of some types of keratotomies. Despite these eff orts, surgical evidence has shown a low success rate because of undercorrection or overcorrection, forcing patients to use spectacles or contact lenses, after surgery, or even leads them to a new procedure. A simulation platform was developed in an attempt to study these surgeries, employing the finite element method, using Matlab and COMSOL Multiphysics simultaneously. The routine is capable of simulate the preoperative cornea in terms of geometry and stress configuration. Also, it could be adapted to simulate any kind of radial keratotomy LASIK and PRK surgeries. Simulations for a double arc keratotomy and a triple arc keratotomy were developed. Results provide evidence of the capability of the platform to improve knowledge of refractive surgery taking into account the possibility to analyze the effect produced by corneal geometry and patient age, which aff ects the elastic modulus of the material, parameters difficult to analyze in an in-vivo experiment. Besides, it demonstrates the potential of the program as a tool for the surgeon to plan refractive surgery.

A prospective clinical study of radial keratotomy in Koreans

Three hundred and forty-eight eyes (246 patients, both eye radial keratototmy in 102 patients) which could be followed-up for at least one year or more were included in this study. Postoperative uncorrected visul acuity which was 20/40 or more could be obtained in 79% of the lower myopic eyes (-1.75--2.75 D), in 73% of the moderate myopic eyes (-3.00--5.75 D) and in 34% of high myopic eyes (-6.00 D-). The postoperative refractive correction (spherical equivalent) ranged from plano to -9.0 D with a mean decrease of -3.86 D with a mean reduction of keratometry in moderate myopia of 3.33 D with a range from 0.5 D to 6.75 D. But its mean reduction in high myopia did not parallel its myopic degree. Glare and fluctuation of vision were the most frequent complaints following surgery. Some patients had continuous constant vision improvement for a long period while some patients (or other eyes) had episodes of decreased vision because of the recurrence of myopia or hyperopia shift. The mean central corneal endothelial cell loss determined 6-l2 months later was 5.31-5.61%. Microperforation in 11 eyes (3%) occurred during the early part of the study and improved naturally without any problem. An over-correction of more than +1.0 D (2%) and an under-correction of more than -1.0 D (1%) with having induced or residual astigmatism (17%) were observed. Radial keratotomy is suceessful in carefully selected patients with mild and moderate myopia, and also in anisometropic high myopia.