Procedimiento de reconstrucción de la topografía corneal a partir de datos altímetros o de curvatura

Número de publicación: ES2392619 A1 (12.12.2012) También publicado como: ES2392619 B1 (22.10.2013) Número de Solicitud: Consulta de Expedientes OEPM (C.E.O.) P201000842(08.06.2010)Procedimiento de reconstrucción de la topografía corneal a partir de datos altimétricos o de curvatura. La invención consiste en un método de reconstrucción de la superficie de la cara anterior de la córnea, a partir de los datos medidos en un conjunto discreto de puntos por medio de un topógrafo corneal o equipo equivalente. Se trata de un procedimiento que obtiene una expresión analítica de la superficie, combinando un ajuste por polinomios de Zernike o con esfera de mejor ajuste, con una reconstrucción por funciones de base radial gaussianas. Se logra obtener una descripción detallada de la superficie corneal, permitiendo un diagnóstico más fiable de patologías, o la implementación de tratamientos customizados. Este procedimiento es fácilmente implementable en cualquier topógrafo corneal, tomógrafo de coherencia óptica, equipos de lámpara de hendidura y equivalentes, de los existentes en el mercado, como sustituto del método estándar basado en polinomios de Zernike.Universidad de Almerí

基于角膜地形图的泪膜视频预处理

在基于角膜地形图的泪膜稳定性评估中,针对眼动、睫毛反射和背景干扰,本文提出了一种泪膜视频的预处理算法。首先,利用索贝尔算子(Sobel operator)进行模糊图像检测,然后对灰度图像进行形态学开运算以获取环状图样凸显的目标图像,再通过霍夫圆检测以及快速傅里叶变换提取目标图像的环状图样频率,依据环状图样频率对目标图像进行带通滤波。最后,二值化及形态学闭运算用于确定环状图样区域。本文从数据库中随机选取10段泪膜视频,应用上述算法逐帧进行泪膜图像处理。实验结果表明,该算法有效地去除了视频序列中的无效图像,并实现了环状图样的定位,为后续泪膜稳定性的评估奠定了基础

Photoplethysmography-Based Biomedical Signal Processing

In this dissertation, photoplethysmography-based biomedical signal processing methods are developed and analyzed. The developed methods solve problems concerning the estimation of the heart rate during physical activity and the monitoring of cardiovascular health. For the estimation of heart rate during physical activity, two methods are presented that are very accurate in estimating the instantaneous heart rate at the wrist and, at the same time, are computationally efficient so that they can easily be integrated into wearables. In the context of cardiovascular health monitoring, a method for the detection of atrial fibrillation using the video camera of a smartphone is proposed that achieves a high detection rate of atrial fibrillation (AF) on a clinical pre-study data set. Further monitoring of cardiovascular parameters includes the estimation of blood pressure (BP), pulse wave velocity (PWV), and vascular age index (VAI), for which an approach is presented that requires only a single photoplethysmographic (PPG) signal. Heart rate estimation during physical activity using PPG signals constitutes an important research focus of this thesis. In this work, two computationally efficient algorithms are presented that estimate the heart rate from two PPG signals using a three axis accelerometer. In the first approach, adaptive filters are applied to estimate motion artifacts that severely deteriorate the signal quality. The non-stationary relationship between the measured acceleration signals and the artifacts is modeled as a linear system. The outputs of the adaptive filters are combined to further enhance the signal quality and a constrained heart rate tracker follows the most probable high energy continuous line in the spectral domain. The second approach is modest in computational complexity and very fast in execution compared to existing approaches. It combines correlation-based fundamental frequency indicating functions and spectral combination to enhance the correlated useful signal and suppress uncorrelated noise. Additional harmonic noise damping further reduces the impact of strong motion artifacts and a spectral tracking procedure uses a linear least squares prediction. Both approaches are modest in computational complexity and especially the second approach is very fast in execution, as it is shown on a widely used benchmark data set and compared to state-of-the-art methods. The second research focus and a further major contribution of this thesis lies in the monitoring of the cardiovascular health with a single PPG signal. Two methods are presented, one for detection of AF and one for the estimation of BP, PWV, and VAI. The first method is able to detect AF based on a smartphone filming the finger placed on the video camera. The algorithm transforms the video into a PPG signal and extracts features which are then used to discriminate between AF and normal sinus rhythm (NSR). Perfect detection of AF is already achieved on a data set of 326 measurements (including 20 with AF) that were taken at a clinical pre-study using an appropriate pair of features whereby a decision is formed through a simple linear decision equation. The second method aims at estimating cardiovascular parameters from a single PPG signal without the conventional use of an additional electrocardiogram (ECG). The proposed method extracts a large number of features from the PPG signal and its first and second order difference series, and reconstructs missing features by the use of matrix completion. The estimation of cardiovascular parameters is based on a nonlinear support vector regression (SVR) estimator and compared to single channel PPG based estimators using a linear regression model and a pulse arrival time (PAT) based method. If the training data set contains the person for whom the cardiovascular parameters are to be determined, the proposed method can provide an accurate estimate without further calibration. All proposed algorithms are applied to real data that we have either recorded ourselves in our biomedical laboratory, that have been recorded by a clinical research partner, or that are freely available as benchmark data sets

Optimisation of the ablation profiles in customised treatments for laser corneal refractive surgery

El propósito de este trabajo es estudiar la posibilidad de realizar cirugía refractiva personalizada reduciendo al mínimo la cantidad de tejido extirpada sin comprometer la calidad visual, así como evaluar la aplicación de estos métodos para reducir al mínimo el tejido ablación a la minimización objetivo de profundidad y el tiempo de ablaciones personalizadas. Se desarrolló un nuevo algoritmo para la selección de un conjunto de términos de Zernike optimizado en los tratamientos personalizados para cirugía láser refractiva corneal. Sus atributos de ahorro de tejido se han simulado en 100 aberraciones de onda diferentes en 6 mm de diámetro. Los resultados de la simulación se evaluaron en términos de cuánta profundidad y volumen se redujo para cada condición (en micras y en porcentaje), si la corrección propuesta consiste en una corrección completa de frente de onda o de un tratamiento libre de aberración, y si la profundidad o el volumen propuesto fue menor que la requerida para el tratamiento equivalente libre de aberración. Los resultados clínicos y los atributos de ahorro de tejido fueron evaluados en dos grupos (minimizar la profundidad: MD, y minimizar el volumen: MV; 30 ojos cada uno), más un grupo control (frente de onda corneal: CW, 30 ojos). Los resultados clínicos fueron evaluados en términos de previsibilidad, seguridad y sensibilidad al contraste. Los resultados de la simulación mostró una profundidad media ahorrada de 5μm (0-16μm), y un volumen medio salvado de 95nl (0-127nl) o una reducción de 11% en tejido (0-66% ahorro de tejido). La correcciones propuestas siempre fueron menos profundas que las correcciones de frente de onda completo y en el 59% de los casos fueron menos profundos que los tratamientos equivalentes libres de aberraciones. En un primer caso, la ablación se redujo significativamente en un 15% en comparación con la corrección personalizada completa. La refracción se corrigió a niveles subclínicos, la agudeza visual sin corrección mejoró a 20/20, la agudeza visual mejor corregida aumentó en 2 líneas, las aberraciones se redujeron aproximadamente un 40% en comparación con los niveles basales preoperatorios, y la zona óptica funcional de la córnea se amplió en aproximadamente un 40% en comparación con los niveles basales preoperatorios. Se redujeron trébol, coma, aberración esférica, y RMS de las aberraciones de orden superior. En la evaluación clínica, el 93% de los tratamientos CW, el 93% en el grupo MD y 100% en el grupo MV se encontraron dentro de 0,50 D de la SEq después de la operación. El 40% de los tratamientos CW, el 34% en el grupo MD y 47% en el grupo MV mejoró por lo menos una línea de AVMC después de la operación. El ahorro de tejido arrojó una reducción media de 8μm (1-20μm) y un ahorro de tiempo de 6s (1-15s) en el grupo de MD, y 6μm (0-20μm) y el 8 (2-26s) en el grupo MV

New Horizons in Ocular Surface and Dry Eye Evaluation

Although considered to be the most important of all the human senses, the delicate nature of the human eye gives rise to many potential defects that could impact the quality of sight and if left untreated eventually lead to permanent vision loss. Scientists and engineers have studied human vision with a desire to better understand and diagnose conditions that may compromise sight. With the never-ending advancement of technology, new avenues of exploration are continually becoming available which can offer the potential for reduced invasiveness whilst extracting even greater diagnosis fidelity. Nevertheless, even with new technological possibilities, many potential solutions are not suited to day to day clinical environments and may be cost prohibitive or simply unreasonably complex to perform. In many cases subjective observation techniques introduced over a century ago still find favour today and may be preferred over newer methods due to large accessibility and low training requirements. This thesis is an exploration of cutting-edge technical approaches and developments with the intention of applying them in an original yet rational fashion to achieve mainstream use in real day to day clinical settings for the provision of superior dry eye diagnosis capabilities. The following research will be focused on identifying anterior eye conditions, in particular dry eye which is growing in prevalence and affecting younger age groups. Rather than restricted, in depth focus on a particular technique, this work will consider several unique approaches and lay a strong argument for their viability and subsequent clinical testing in separate, future work. Chapter 2 focuses on improving the commonly used technique of sodium fluorescein viewing with custom created blue excitation and yellow emission filters. Although such subjective fluorescein observation techniques have existed for many years, the custom filters offer a large improvement in viewing performance, filter efficiency and slit lamp hands free usage, and are ready to scale to production with 1,000 units already manufactured and a further 16,000 units on order. Chapter 3 describes research on determining the thickness and degradation of the transparent tear film over the course of a blinking cycle. To date, many attempted measures have produced results with an accepted value in the region of 5 μm. Tear dynamics; refresh, spreading and degradation behaviours are key in providing insight into the stability and premature breakdown leading to dry eye disease, all of which are demonstrated as possible with confocal and interferometric technologies being examined and an average tear film thickness value 3.28 μm and degradation rate of 0.048 ± 0.034 μm-2 being achieved. Lastly, chapter 4 introduces a new anterior eye assessment instrument based on the technique of persistence of vision that is capable of enhancing the ability to detect tear film break up time in a new low cost, non- invasive device. A plethora of additional anterior eye examinations such as corneal topography and slit lamp viewing capabilities are also made possible with this new projection method. The POV scope is a distinctive new approach to anterior eye viewing and gives the ability to capture high resolution, high contrast images that in the near future may be coupled to a machine learning platform to provide a clear diagnosis for common conditions including the multifactorial and inconsistent signs and symptoms of dry eye disease

Modelado geométrico personalizado de la córnea humana y su aplicación a la detección de ectasias corneales

[SPA] La córnea es una estructura biológica viva cuya arquitectura presenta una morfología singular, ya sea en un estado natural o patológico. Esta singularidad ha sido caracterizada a lo largo de toda la historia en el campo de la oftalmología y la óptica a través de la generación de modelos genéricos o de modelos personalizados de la córnea humana. Hoy en día, el desarrollo de nuevas tecnologías permite caracterizar la morfología corneal a partir de los denominados equipos topográficos; estos equipos aportan una caracterización personalizada de índole cualitativa y cuantitativa al médico oftalmólogo. Sin embargo, los sistemas de diagnóstico de las patologías corneales están basados en unos índices de valoración de la irregularidad de las superficies corneales que son calculados a partir de algoritmos específicos internos para cada topógrafo corneal y de los cuales se desconoce su programación. Por este motivo en esta tesis doctoral se establece un nuevo procedimiento fundamentado en la geometría computacional para obtener un modelo sólido 3D personalizado in vivo de la córnea humana utilizando herramientas de Diseño Geométrico Asistido por Ordenador. Este modelo virtual reconstruye fidedignamente las superficies de la cara anterior y posterior de la córnea, a partir de unos datos aportados por los topógrafos corneales denominados datos en bruto (sin ningún trato mediante algoritmo) tanto para los ojos de pacientes sanos como para los ojos de pacientes diagnosticados con la patología ectásica más común, el queratocono. A partir del nuevo modelo sólido obtenido, se definen unos índices de caracterización de la morfología corneal basados en variables geométricas, los cuales pueden ser utilizados como unos nuevos índices de diagnóstico de la patología ectásica objeto de estudio debido a que presentan una elevada sensibilidad y especificidad para su diagnóstico. [ENG] The cornea is a living biological structure whose architecture has a unique morphology, either in a natural or diseased condition. This uniqueness has been characterized throughout all history in the field of ophthalmology and optics through the generation of generic or customized models of human cornea. Today, the development of new technologies leads to characterize the corneal morphology from the so‐called topographic devices; these devices provide a personalized qualitative and quantitative characterization of its nature for the ophthalmologist. However corneal pathological diagnosis systems are based on indicators of the irregularity of the corneal surfaces, which are calculated from specific internal algorithms for each corneal topographer and whose programming is unknown. For that reason, this doctoral thesis establishes a new procedure based on computational geometry to obtain a 3D solid model, personalized and in vivo of the human cornea by using Computer Aided Geometrical Design tools. This virtual model represents accurately both the anterior and posterior corneal surfaces from a set of raw data (without any algorithm treatment) provided by the corneal topographers for both healthy corneas and corneas with the most common ectasic disease, the keratoconus. The new solid model obtained is later analyzed to define a set of indices that enable the characterization of the corneal morphology and that are based on geometric variables. These indices can be used as new indicators for the diagnosis of the keratoconus disease due to their high sensibility and specificity.[ENG] The cornea is a living biological structure whose architecture has a unique morphology, either in a natural or diseased condition. This uniqueness has been characterized throughout all history in the field of ophthalmology and optics through the generation of generic or customized models of human cornea. Today, the development of new technologies leads to characterize the corneal morphology from the so‐called topographic devices; these devices provide a personalized qualitative and quantitative characterization of its nature for the ophthalmologist. However corneal pathological diagnosis systems are based on indicators of the irregularity of the corneal surfaces, which are calculated from specific internal algorithms for each corneal topographer and whose programming is unknown. For that reason, this doctoral thesis establishes a new procedure based on computational geometry to obtain a 3D solid model, personalized and in vivo of the human cornea by using Computer Aided Geometrical Design tools. This virtual model represents accurately both the anterior and posterior corneal surfaces from a set of raw data (without any algorithm treatment) provided by the corneal topographers for both healthy corneas and corneas with the most common ectasic disease, the keratoconus. The new solid model obtained is later analyzed to define a set of indices that enable the characterization of the corneal morphology and that are based on geometric variables. These indices can be used as new indicators for the diagnosis of the keratoconus disease due to their high sensibility and specificity.Esta tesis se ha realizado en parte gracias a la financiación del proyecto del Fondo Europeo de Desarrollo Regional (FEDER) y del Ministerio Español de Economía y Competitividad, Instituto Carlos III, Red Temática de Investigación Cooperativa en Salud (RETICS) «Prevención, detección precoz y tratamiento de la patología ocular prevalente, degenerativa y crónica». Subprograma «dioptrio ocular y patologías frecuentes» (RD12/0034/0007).Escuela Internacional de DoctoradoUniversidad Politécnica de CartagenaPrograma Oficial de Doctorado en Tecnologías Industriale

Ocular morphology in people with Down's syndrome

The study describes the morphology of eyes in children and adults with Down's syndrome (DS) including ocular biometric parameters (axial length, cornea, anterior chamber, lens and pupil size) and retinal features. There was no significant difference in the correlation of axial length and refraction between DS children (n=46) and controls (n=50). Children with DS (n=18) and adults with DS (n=10) have significantly thinner corneas both in the centre and periphery, smaller corneal radius, higher corneal power, higher corneal aberration and lower lens power compared to their respective control children (n=28) and adults (n=16). Further, in spite of abnormal ocular parameters, refraction in people with DS appeared to be determined by a similar correlation between those parameters as in controls. A larger disc and rim were found in children with DS (n=17) compared to controls (n=28). An increased number of vessels were found in periphery of the retina in children with DS. However, there was a similar distribution of retinal vessels in DS children (n=31) and controls (n=40). The presence of the peripapillary atrophy in children (67%) was much higher than that of controls (28%). No significant correlation was found between the total number of vessels and visual function such as refraction, visual acuity and accommodation among children with DS. Keratoconus was present in 8 adults with DS, however, no keratoconus was found in children with DS but abnormal corneal topography was more common in children with DS compared to that in controls.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Ocular morphology in people with Down's syndrome

The study describes the morphology of eyes in children and adults with Down's syndrome (DS) including ocular biometric parameters (axial length, cornea, anterior chamber, lens and pupil size) and retinal features. There was no significant difference in the correlation of axial length and refraction between DS children (n=46) and controls (n=50). Children with DS (n=18) and adults with DS (n=10) have significantly thinner corneas both in the centre and periphery, smaller corneal radius, higher corneal power, higher corneal aberration and lower lens power compared to their respective control children (n=28) and adults (n=16). Further, in spite of abnormal ocular parameters, refraction in people with DS appeared to be determined by a similar correlation between those parameters as in controls. A larger disc and rim were found in children with DS (n=17) compared to controls (n=28). An increased number of vessels were found in periphery of the retina in children with DS. However, there was a similar distribution of retinal vessels in DS children (n=31) and controls (n=40). The presence of the peripapillary atrophy in children (67%) was much higher than that of controls (28%). No significant correlation was found between the total number of vessels and visual function such as refraction, visual acuity and accommodation among children with DS. Keratoconus was present in 8 adults with DS, however, no keratoconus was found in children with DS but abnormal corneal topography was more common in children with DS compared to that in control

Enhancing the Standard Operating Range of a Placido Disk Videokeratoscope for Corneal Surface Estimation

Abstract—Corneal topography estimation that is based on the Placido disk principle relies on good quality of precorneal tear film and sufficiently wide eyelid (palpebral) aperture to avoid reflections from eyelashes. However, in practice, these conditions are not always fulfilled resulting in missing regions, smaller corneal coverage, and subsequently poorer estimates of corneal topography. Our aim was to enhance the standard operating range of a Placido disk videokeratoscope to obtain reliable corneal topography estimates in patients with poor tear film quality, such as encountered in those diagnosed with dry eye, and with narrower palpebral apertures as in the case of Asian subjects. This was achieved by incorporating in the instrument’s own topography estimation algorithm an image processing technique that comprises a polar-domain adaptive filter and amorphological closing operator. The experimental results from measurements of test surfaces and real corneas showed that the incorporation of the proposed technique results in better estimates of corneal topography, and, in many cases, to a significant increase in the estimated coverage area making such an enhanced videokeratoscope a better tool for clinicians