Intelligent Planning for Refractive Surgeries: A Modelling and Visualisation-based Approach

Laser refractive surgeries have been commonly used in ophthalmic operations. Considerable research has been carried out and encouraging progress made in recent years. It covers properties of the cornea and behaviour of tissue in different parts of the eye, topography and material expression of individual patient's eyes, prediction using finite element (FE) analysis to estimate the corneal shape change and the change in refractive power. Further effort is still required to advance the research to aid the decision making for laser refractive surgeries. This study comprehensively reviews the latest techniques of refractive surgery and research on computational analysis and modelling techniques and their applications, especially the current prediction and planning techniques for laser refractive surgeries. The aim of this study is to develop an intelligent assistant tool for the laser refractive surgeries with prediction and visualisation functions. For this aim, two objectives will be achieved: prediction with the clinical dataset and human vision simulation. Due to clinical statistics, the clinical dataset is often incomplete, imbalanced, and sparse. Three methods are proposed to predict surgery parameters and outcomes using the clinical dataset. A multiple imputation method, with multiple regression, is proposed for imputing the missing data. For the imbalance of data distribution in the clinical dataset, an over-sampling of the minority data method is proposed. The accuracy of predicted minority data is close to the accuracy of predicted majority data. Finally an ensemble learning method which is optimised by the genetic algorithm is proposed to improve the accuracy of the prediction results with a sparse dataset. According to the distribution of the sample in the clinical data, the percentage of unacceptable results is 23.02%. The methods in this study could provide an accuracy of 79.02% to find the possible unacceptable cases, that is, the method could reduce the percentage of unacceptable results from 23.02% to 4.82%. In human vision simulation, the study focuses on how the human vision simulation could be determined and obtained accurately within a required timeframe. The ray tracing technique can provide more precise results than the rasterisation technique, especially for the simulation of light reflection and refraction in the human eyeball. However, the thin lens assumption affects the accuracy of the pathological vision simulation with the ray tracing technique. An improved schematic human eye model is proposed to obtain a numerical model predicting the size of the defocus blur for the pathological vision, which wraps the shape of the ray intersection area. In order to generalise this model to other healthy and pathological vision, an intelligent blur range derivation method is proposed. On the other hand, ray tracing scene rendering requires repeated iterative computing which takes a significant amount of computation time. A GPU-based ray tracing computing method is proposed to accelerate and optimise the rendering of scenes. With this method, the scene rendering speed is about 75 times faster than using the CPU

Outcome of PRK in low to moderate myopia using Mel 80 Excimer laser platform

INTRODUCTION: Myopia / short sightedness is a refractive error in which the parallel rays of light from infinity come to focus in front of the retina when the eye is at rest, thus grossly reducing the vision. Myopia could be axial due to elongation of anteroposterior diameter of the eyeball or curvature myopia due to increase in radius of curvature of the cornea; and index myopia due to change in refractive index of lens, cornea, aqueous and vitreous, thus increasing the dioptric power of the eye. Photorefractive keratectomy (PRK) consists of the application of energy ofthe ultraviolet range generated by an argon fluoride (ArF) excimer laser to the anterior corneal stroma to change its curvature and, thus, to correct a refractive error. The physical process of remodeling the corneal stroma by ultraviolet (193 nm wavelength) high-energy photons is known as photoablation. AIM OF THE STUDY: To study the outcome of Photo Refractive keratectomy performed inpatients with low to moderate myopia using Mel 80 Excimer laser System. RESULTS: In this prospective, randomized study, 46 eyes of 23 patients belonging to the mild myopia group (-1 D to –6D), 44 eyes of 22 patients belonging to moderate group (-6D to –12D) who underwent PRK between the period of September 2005 to September 2006 at the Institute of Ophthalmology, Joseph Eye Hospital, Trichy, were included in the study. SUMMARY: In this prospective study, 90 eyes of 45 patients underwent PRK with Mel 80 Excimer laser system of which 46 eyes were of low myopia and 44 eyes were of moderate myopia. Preoperative uncorrected visual acuity, BCVA, spherical equivalent, topography, corneal thickness, keratometry and pupil diameter were recorded for all the patients. PRK was done for all the patients in an attempt to achieve the preoperative BCVA. Postoperative UCVA was recorded for all the patients on Day 1, 3day and six months Pre-operative and post-operative BCVA was compared which was found to be statistically significant. There was no postoperative decrease in vision during the 6 months followup. There was no retreatment in this study Importantly, the safety profile of PRK was found to be excellent. CONCLUSION The findings in this study are significant, showing good unaided postoperative visual acuity with excellent safety profile. Overall patient satisfaction with this procedure is high with Mel 80 laser system, which is comparable to other 5th generation laser systems. The emergence of better laser nomograms, larger optical zones and improved understanding of aberrations and their significance will lead to improvements in patient outcome in future. PRK can be considered an alternative treatment procedure for myopic patient whose corneal thickness is inadequate for laser in situ keratomileusis (LASIK)

Clinical Applications of Anterior Segment Optical Coherence Tomography:An Updated Review

Since its introduction, optical coherence tomography (OCT) has revolutionized the field of ophthalmology and has now become an indispensable, noninvasive tool in daily practice. Most ophthalmologists are familiar with its use in the assessment and monitoring of retinal and optic nerve diseases. However, it also has important applications in the assessment of anterior segment structures, including the cornea, conjunctiva, sclera, anterior chamber, and iris, and has the potential to transform the clinical examination of these structures. In this review, we aim to provide a comprehensive overview of the potential clinical utility of anterior segment OCT (AS-OCT) for a wide range of anterior segment pathologies, such as conjunctival neoplasia, pterygium, scleritis, keratoconus, corneal dystrophies, and infectious/noninfectious keratitis. In addition, the clinical applications of AS-OCT (including epithelial mapping) in preoperative planning and postoperative monitoring for corneal and refractive surgeries are discussed

Determining the Influence of Environment and Minimizing Residual Roughness in Laser Corneal Refractive Surgery

Aims: This dissertation deals with multiple topics, with a global aim of determining the influence of environment and minimizing residual roughness in laser corneal refractive surgery. The multiple topics under consideration are listed below: •TOPIC A: To analyze the effect of seasonal changes in PMMA Performance using the SCHWIND AMARIS laser system •TOPIC B: To analyze impact of various humidity and temperature settings on excimer laser ablation of PET, PMMA and porcine corneal tissue •TOPIC C: To analyze the impact of residual roughness after corneal ablation in perception and vision •TOPIC D: To outline a rigorous simulation model for simulating shot-by-shot ablation process. Furthermore, to simulate the impact of laser beam characteristics like super Gaussian order, truncation radius, spot geometry, spot overlap and lattice geometry on ablation smoothness. •TOPIC E: To test the impact of laser beam truncation, dithering, and jitter on residual roughness after PMMA ablations, using a close-to-Gaussian beam profile. Methods: TOPIC A: By analyzing PMMA and PET ablation performance by a large series of AMARIS laser systems (Schwind eye-tech solutions, Germany) inside a climate controlled environment, the influence purely coming from the seasonal changes was investigated in a large scale retrospective cross sectional review. Seasonal outcomes were evaluated in terms of PMMA and PET Performance stratified for every month in a year, as well as stratified for each season in a year. TOPIC B: A Study was conducted using AMARIS system placed inside a climate chamber. Ablations were performed on PET, PMMA and porcine cornea. Impact of wide range of temperature (~18°C to ~30°C) and relative humidity (~25% to ~80%) on laser ablation outcomes was tested using nine climate test settings. Multiple linear regression was performed using least square method with predictive factors: Temperature, Relative Humidity, Time stamp. Influence of climate settings was modelled for Pulse Energy, Pulse Fluence, ablation efficiency on PMMA and porcine cornea tissue. TOPIC C: The Indiana Retinal Image Simulator (IRIS) was used to simulate the polychromatic retinal image. Using patient-specific Zernike coefficients and pupil diameter, the impact of different levels of chromatic aberrations was calculated. Corneal roughness was modeled via both random and filtered noise, using distinct pre-calculated higher order Zernike coefficient terms. The outcome measures for the simulation were simulated retinal image, Strehl Ratio and Visual Strehl Ratio computed in frequency domain. The impact of varying degree of roughness, spatial frequency of the roughness, and pupil dilation was analyzed on these outcome measures. TOPIC D: Given the super Gaussian order, the theoretical beam profile was determined following Lambert-Beer model. The intensity beam profile originating from an excimer laser was measured with a beam profiler camera. For both, the measured and theoretical, beam profiles, two spot geometries (round and square spots) were considered, and two types of lattices (reticular and triangular) were simulated with varying spot overlaps and ablated material (cornea or PMMA). The roughness in ablation was determined by the root-mean-square per square root of layer depth. TOPIC E: A study was conducted using a modified AMARIS system. For the PMMA ablations, two configurations (with a 0.7mm pinhole and 0.75mJ and without pinhole and 0.9mJ (for fluences of 329mJ/cm2 and 317mJ/cm2 and corneal spot volumes of 174pl and 188pl)) were considered, along with two types of lattices (with and without ordered dithering to select the optimum pulse positions), and two types of spot placement (with and without jitter). Real ablations on PMMA (ranging from -12D to +6D with and without astigmatism) completed the study setup. The effect of the 2x2x2 different configurations was analyzed based on the roughness in ablation estimated from the root mean square error in ablation. Results: TOPIC A: The seasons winter and summer showed statistical significant variations with respect to the global values for all the tested parameters except the nominal number of laser pulses for high and low fluence setting. The metric technical performance of the analyzed systems showed a stronger PMMA ablation performance in summer time compared to a weaker performance in the winter time, with the maximum seasonal deviation of 6%. The results were consistently confirmed in seasonal as well as monthly analyses. TOPIC B: Temperature changes did not affect laser pulse energy, pulse fluence (PET), and ablation efficiency (on PMMA or porcine corneal tissue) significantly. Changes in relative humidity were more critical and significantly affected laser pulse energy, high fluence and low fluence. Opposite trend was observed between the ablation performance on PMMA and porcine cornea. TOPIC C: In case of a constant roughness term, reducing the pupil size resulted in improved outcome measures and simulated retinal image. The calculated image quality metrics deteriorated dramatically with increasing roughness. Clear distinction was observed in outcome measures for corneal roughness simulated as random noise compared to filtered noise, further influenced by the spatial frequency of filtered noise. TOPIC D: Truncating the beam profile increased the roughness in ablation, Gaussian profiles theoretically resulted in smoother ablations, round spot geometries produced lower roughness in ablation compared to square geometry, triangular lattices theoretically produced lower roughness in ablation compared to the reticular lattice, theoretically modelled beam profiles showed lower roughness in ablation compared to the measured beam profile, and the simulated roughness in ablation on PMMA tend to be lower than on human cornea. For given input parameters, proper optimum parameters for minimizing the roughness has been found. TOPIC E: Truncation of the beam was negatively associated to a higher level of residual roughness; ordered dithering to select the optimum pulse positions was positively associated to a lower level of residual roughness; jitter was negatively associated to a higher level of residual roughness. The effect of dithering was the largest, followed by truncation, and jitter had the lowest impact on results. Conclusions: The large scale retrospective cross sectional study presented in this work, demonstrated a cyclic winter-summer variation in PMMA ablation using the AMARIS lasers. These seasonal variations were further substantiated with the experiments conducted in the climate chamber, over a wide range of temperature and humidity. Temperature changes did not affect laser pulse energy, pulse fluence, and ablation efficiency (on PMMA or porcine corneal tissue) significantly. However, changes in relative humidity were more critical and significantly affected laser pulse energy, high fluence and low fluence. The proposed well-fitting multi-linear model can be utilized for compensation of temperature and humidity changes on ablation efficiency. The relationship between calibration materials like PMMA and corneal tissue shall be analyzed cautiously before designing the calibration routine, in order to obtain optimum outcomes with minimum deviations. Despite its limitations, the simple and robust method proposed here for quantifying the influence of post-ablation roughness on vision and perception, can be utilized in different applications. From the simulations of the shot-by-shot ablation process, a theoretical proper optimum configuration was found for minimizing the roughness in ablation for defined input parameters. The PMMA experiments confirmed the theoretical proper optimum settings in real world conditions. The results and improvements derived out of this work can be directly applied to the laser systems for corneal refractive surgery, to help reduce the complications and occurrence of adverse events during and after refractive surgery, and improve the short term and long term postoperative clinical outcomes

Intraocular Lens

The first clinical application of intraocular lens (IOL) goes back to 1949 when Dr. Harold Ridley successfully implanted a PMMA IOL into an eye on 29 November 1949. This innovation is a big step forward for cataract surgery. With development of the IOL material and biocompatibility, more and more IOL types have been used in clinical ophthalmology. This book is the fruit of worldwide cooperation between clinical teams. In this book we discuss the IOL materials and design, aberration and astigmatism correction with IOL, entopic phenomenon of IOL, myopia and phakic IOL, and secondary IOL techniques. We believe that this content provides the readers with a comprehensive knowledge of the latest developments of IOL

The role of dry eye disease in cataract and refractive surgery

El síndrome de ojo seco (DED) puede jugar un papel importante en las cirugías oftálmicas con fines refractivos tanto corneales (tratamiento corneal laser) como cristalinianas (cirugía de catarata) pero también en aquellas cuyo fin es controlar la presión intraocular en pacientes que sufren de glaucoma. El objetivo principal de esta tesis se refiere a la aplicación de una serie de pruebas diagnósticas, de mínimamente a no-invasivas, sugeridas por el Tear Film & Ocular Society Dry Eye WorkShop II (TFOS DEWS II) que pueden ayudar a mejorar los resultandos refractivos y visuales en la cirugía oftálmica actual. La cirugía de cristalino, particularmente la cirugía moderna de catarata y la refractive lens exchange (RLE), centra la primera sección de la tesis. En realidad, el DED no está presente solo como complicación post-operatoria, sino que también es responsable de resultados refractivos y visuales no deseados dado que parte del examen pre-operatorio en la cirugía del cristalino puede verse influida por una película lagrimal deficiente (por ej. biometría ocular y topografía corneal). La literatura revisada ha demostrado poca información en el uso de técnicas avanzadas para evaluar la película lacrimal en pacientes que se someten a cirugía de cristalino, siendo estos hallazgos los más importantes para evitar resultados subóptimos después de la intervención. Posteriormente, en la cirugía refractiva corneal moderna, a pesar de la seguridad y efectividad en la corrección de errores refractivos tales como miopía, hipermetropía y astigmatismo, el DED post-quirúrgico sigue siendo un problema recurrente y unas de las complicaciones más referidas por los pacientes. Recientemente, nuevas técnicas (por ej. small incision lenticule extraction (SMILE)) han sido introducidas con el fin de reducir el desarrollo de DED. El uso de la microscopia confocal in-vivo, así como un programa automático de análisis, has sido incluidos para proporcionar resultados objetivos más rápido que puedan ser comparados con la cirugía de la córnea tradicional (e.g. laser-assisted in situ keratomileusis (LASIK)).El manejo de glaucoma mediante colirios oculares con preservantes puede llevar a deterioro de la superficie ocular con una larga proporción de pacientes con quejas del DED tanto como signos (como enrojecimiento ocular) tanto como síntomas (como incomodidad ocular, fotofobia, etc.). De los nuevos procedimientos oculares para controlar la presión intraocular reduciendo la necesidad del manejo tópico, la cirugía de glaucoma minimamente invasiva (MIGS) es prometedora también en mejorar la homeostasis de la superficie ocular. Sin embargo, muy poco ha sido investigado y la necesidad de una mejor comprensión ha llevado a administrar una serie de pruebas avanzadas para el diagnóstico de ojo DED con objeto de revelar los resultados a corto plazo sometidos a MIGS. Los estudios de investigación detallados en esta tesis evalúan una serie de técnicas avanzada de diagnóstico para comprender el papel de la DED en los procedimiento actuales de cirugía oftálmica con propósitos refractivos y visuales pero también para el manejo de enfermedades como el glaucoma. Asimismo, dichos estudios tratan de descubrir cual son las pruebas más importantes, mínimamente o no-invasivas, capaces de revelar el papel del DED en la cirugía oftálmica que llevarían a una mejora en los resultados tanto refractivos como visuales, así como los referidos por los pacientes.Dry eye disease (DED) can play an important role in ophthalmic procedures with refractive aims such as those involving the cornea (corneal laser surgery) or the crystalline lens (refractive lensectomy or cataract surgery) but also in the treatment of other conditions such as glaucoma. This thesis describes the application of a series of minimally to non-invasive diagnostic DED tests recommended by the recent Tear Film & Ocular Society Dry Eye WorkShop II (TFOS DEWS II) to help to improve the understanding of the impact of dry eye on the refractive and visual outcomes in the ophthalmic surgery and the impact of ophthalmic surgery on the ocular surface. Intraocular lens surgery, in particular modern cataract and refractive lens-exchange (RLE) surgery, is the focus of the first section of the thesis. In fact, DED is not only present as a post-operative complication but can also be responsible for sub-optimal refractive and visual outcomes since parts of the pre-operative examination pathway can be influenced by a depleted tear film (e.g. biometry and corneal topography). A literature review suggests little evidence of the routine use of advanced tear film assessments in patients undergoing intraocular lens surgery and there is little information on which DED findings are most important to avoid suboptimal clinical outcomes. Studies were carried out to explore the most relevant DED tests as recommended by the TFOS DEWS II. The key findings were validated questionnaires such as Ocular Surface Disease Index (OSDI) and Dry Eye Questionnaire 5-items (DEQ-5) and tear metrics such as non-invasive keratograph break-up time (NIKBUT), tear film volume (TMH) and tear osmolarity. In modern corneal refractive surgery, despite numerous publications and studies demonstrating the safety and efficacy in correcting refractive errors such as myopia, hyperopia and astigmatism, post-operative DED is still problematic and of the most common complications after surgery. Recently, newer techniques (e.g. small incision lenticule extraction (SMILE)) have been introduced with the aim of providing excellent visual outcomes whilst overcoming some of the limitations of more established procedures including undesirable alterations to corneal nerve structure and function and DED development. The use of in-vivo confocal microscopy was used to compare corneal nerve structure after SMILE with that seen after traditional laser-assisted in situ keratomileusis (LASIK). The results showed FS-LASIK surgery had more impact on DED symptomatology, TMH and NIKBUT and has led to significant change to the corneal nerve fibre metrics considered than SMILE surgery. Glaucoma management with topical preserved eyedrops can lead to deterioration of the ocular surface in a large proportion of patients with DED issues in terms of signs (e.g. ocular redness) and symptoms (grittiness, photophobia, etc.). Of the newer surgical procedures designed to control intraocular pressure reducing the need for topical management, minimally-invasive glaucoma surgery (MIGS) seems to be promising and could improve the homeostasis of the ocular surface in glaucoma patients. However, very little research on this topic has been published and an advanced pilot investigation to explore the use of a diagnostic battery of tests for DED after MIGS was carried out. Reduction in IOP was achieved by the procedure together with the reduction in DED symptomatology, increase of stability of the tear film and improvement of the ocular surface staining. In summary, the research studies detailed in this thesis use a series of advanced diagnostic techniques primarily to understand the role of DED in patients undergoing ophthalmic procedures for refractive and visual indications but also in patients being treated for glaucoma. They also explore which are the most important tests, in terms of identifying the impact of DED in ophthalmic surgery. Better diagnosis and management of DED in patients undergoing ophthalmic surgery will lead to optimal refractive, visual and patient-reported outcomes

The role of dry eye disease in cataract and refractive surgery

Dry eye disease (DED) can play an important role in ophthalmic procedures with refractive aims such as those involving the cornea (corneal laser surgery) or the crystalline lens (refractive lensectomy or cataract surgery). This thesis describes the application of a series of minimally to non-invasive diagnostic DED tests recommended by the recent Tear Film & Ocular Society Dry Eye WorkShop II (TFOS DEWS II) to help to improve the understanding of the impact of dryeye on the refractive and visual outcomes in the ophthalmic surgery and the impact of ophthalmic surgery on the ocular surface.Intraocular lens surgery, in particular modern cataract and refractive lens-exchange (RLE) surgery, is the focus of the first section of the thesis. In fact, DED is not only present as a post-operative complication but can also be responsible for sub-optimal refractive and visual outcomes since parts of the pre-operative examination pathway can be influenced by a depleted tear film (e.g. biometry and corneal topography). A literature review suggests little evidence ofthe routine use of advanced tear film assessments in patients undergoing intraocular lens surgery and there is little information on which DED findings are most important to avoid suboptimal clinical outcomes. Studies were carried out to explore the most relevant DED tests as recommended by the TFOS DEWS II. The key findings were that pre-operative DED metrics such as reduced tear meniscus height (<0.20 mm) together with increased DED symptoms measured with Ocular Surface Disease Index (OSDI) (score ≥13) were potentially relevant to increase the chance of having less accurate refraction and poorer visual outcomes after lens surgery. Contrarily, Dry Eye Questionnaire 5-items (DEQ-5), that is a useful tool to evaluate ocular comfort, might be not designed to consider visual function that could potentially be affected by DED or cataract and might be not a good sensitive indicator of the refractive and visual outcomes after lens surgery.In modern corneal refractive surgery, despite numerous publications and studies demonstrating the safety and efficacy in correcting refractive errors such as myopia, hyperopia and astigmatism, post-operative DED is still problematic and of the most common complications after surgery. Recently, newer techniques (e.g. small incision lenticule extraction (SMILE)) have been introduced with the aim of providing excellent visual outcomes whilst overcoming some of the limitations of more established procedures including undesirable alterations to corneal nerve structure and function and DED development. The use of in-vivo confocal microscopy was used to compare corneal nerve structure after SMILE with that seen after traditional laser-assisted in situ keratomileusis (LASIK). The results showed FS-LASIK surgery had more impact on the corneal nerve fibre metrics (up to 75% of reduction) compared to SMILE surgery (up to 23%). Additionally, DED symptoms after FS-LASIK observed a significant two to four-fold increase (OSDI and DEQ-5) where also tear volume significantly decreased after surgery (from 0.32 ± 0.13 to 0.22 ± 0.09 mm).In summary, the research studies detailed in this thesis use a series of advanced diagnostic techniques primarily to understand the role of DED in patients undergoing ophthalmic procedures for refractive and visual indications. They also explore which are the most important tests, in terms of identifying the impact of DED in ophthalmic surgery. Better diagnosis and management of DED in patients undergoing ophthalmic surgery will lead to optimal refractive, visual and patient-reported outcomes

Advances in Ophthalmology

This book focuses on the different aspects of ophthalmology - the medical science of diagnosis and treatment of eye disorders. Ophthalmology is divided into various clinical subspecialties, such as cornea, cataract, glaucoma, uveitis, retina, neuro-ophthalmology, pediatric ophthalmology, oncology, pathology, and oculoplastics. This book incorporates new developments as well as future perspectives in ophthalmology and is a balanced product between covering a wide range of diseases and expedited publication. It is intended to be the appetizer for other books to follow. Ophthalmologists, researchers, specialists, trainees, and general practitioners with an interest in ophthalmology will find this book interesting and useful

Optical Methods in Sensing and Imaging for Medical and Biological Applications

The recent advances in optical sources and detectors have opened up new opportunities for sensing and imaging techniques which can be successfully used in biomedical and healthcare applications. This book, entitled ‘Optical Methods in Sensing and Imaging for Medical and Biological Applications’, focuses on various aspects of the research and development related to these areas. The book will be a valuable source of information presenting the recent advances in optical methods and novel techniques, as well as their applications in the fields of biomedicine and healthcare, to anyone interested in this subject