Five Steps To Start Your Refractive Surgery. This book: Although there are numbers of textbooks in regard with refractive surgery in the market, readers feel that they cannot find all what they need in only one book. They also feel that they have to read much to find what exactly they are looking for. In addition, in spite of the vast number of refractive surgery courses conducted during conferences, the audience may feel that they do not get answers to all the questions that rise in their mind. Moreover, during daily practice, refractive surgeons may wish to own a quick reference in their hands that is well ordered and easy to deal with. All the above reasons were behind writing this handbook. To make information easily accessible, simple language was used, a tabulated text was written, and a step-by-step systematic methodology was applied. Together with comprehensive illustrations, clinical aspects were integrated into basics to make use of any tiny information. To reach this goal, this handbook was composed of five steps consisting of nine chapters. Step one consists of four chapters dealing with corneal imaging and its clinical application in refractive surgery. Step two has one chapter discussing major refractive procedures. Step three has one chapter describing rules and recommendations in refractive surgery. Step four is a start-off step, consisting of two chapters about approaching the candidate and dealing with refractive surgery complications. Step five presents clinical case-study. Chapter 1: Corneal Imaging It describes clinical basics of corneal topography and tomography in regard with the Scheimpflug-based tomographer, the Pentacam, and discusses all corneal parameters and the main refractive maps in terms of normal, suspected and abnormal findings with clinical interpretation of these findings. Risk factors for refractive surgery are well highlighted, such as abnormal patterns of the curvature, elevation and pachymetry maps, pachymetry profiles, and corneal topometry. This chapter also describes topographic and tomographic features of ectatic corneal disorders such as keratoconus, pellucid marginal degeneration (PMD), pellucid-like keratoconus (PLK) and forme fruste keratoconus (FFKC). Chapter 2: Wavefront Science Basics of wavefront science are well described in a simple way to be as an introduction to the full demonstration of types of low order (LOAs) and high order aberrations (HOAs). Defocus, tilt, astigmatic, spherical, coma, trefoil and other aberrations are illustrated and clinically interpreted. Methods for measuring aberrations are explained, these includes point spread function (PSF), Strehl ratio, modulation transfer function (MTF), root mean square (RMS) and Zernike coefficients (ZCs). Wavefront maps, changes of aberrations with age, and high order aberrations (HOAs) found in forme fruste keratoconus are also discussed. Chapter 3: Optical Coherence Tomography Anterior optical coherence tomography (anterior OCT) is, day-by-day, taking an important role in both the diagnosis and treatment parts of refractive surgery. Many complications are better diagnosed by anterior OCT, and the treatment of some corneal pathologies can better be guided by this tool. This unique chapter describes the application of anterior OCT as a diagnostic tool and as a guide-for-management tool in terms of refractive surgery. As a diagnostic tool, anterior OCT can be used to diagnose some corneal lesions, such as sub Bowman’s calcifications, Salzmann’s nodular degeneration and posterior corneal abnormality; LASIK flap complications; double anterior chamber after deep anterior lamellar keratoplasty (DALK); keratoglobus; and for keratoconus detection. As a guide-for-management tool, anterior OCT can be used to guide therapeutic photorefractive keratectomy (PTK), post photoablation enhancement, post corneal cross linking follow up – by detecting the demarcation line, and implantation of phakic IOL (PIOL). Chapter four: Corneal Biomechanics By time, corneal biomechanics are getting an important role in the field of refractive surgery. When the importance of corneal biomechanics was recognized, the effect of keratorefractive surgery on the dynamic behavior of corneal tissue could be understood, and post operative complications, with ectasia being the most important, could be explained. The basics and the part of corneal biomechanics in decision making are well discussed in this chapter in addition to the properties of corneal tissue such as viscoelasticity, rigidity and corneal hysteresis. Moreover, the impact of corneal biomechanics on myopic and hyperopic treatment results is explained, and their role in iatrogenic post operative irregularities and ectasia is clarified. Corneal biomechanics have an effect on IOP measurement and glaucoma prediction, which is also mentioned in this chapter. This chapter also describes measurement of corneal biomechanics by the ocular response analyzer (ORA), and interprets the ORA waveform and parameters. Chapter Five: Main Refractive Options This chapter discusses refractive surgery options in depth. It starts with the three types of photorefractive surgery, consisting of surface, lamellar and surface-lamellar ablation. Types of surface ablation are described, including photorefractive keratectomy (PRK), laser subepithelial keratomileusis (LASEK), Epipolis LASIK (Epi-LASIK), trans epithelial photorefractive keratectomy (Trans-PRK) and phototherapeutic keratectomy (PTK). Types of lamellar ablation are also described, including laser in situ keratomileusis (LASIK) and femtosecond LASIK. Sub Bowman keratomileusis (SBK) is finally discussed as a surface-lamellar technique. What is important here is that all details are demonstrated in depth in a tabulated text in terms of definitions, differences, comparisons, advantages and disadvantages, and contraindications. Moreover, pre- and intra-operative considerations are mentioned in regard with anaesthesia, sterilization, draping, alignment and registration, in addition to different surgical techniques, such as methods of epithelial removal, techniques of flap creation, and centration and decentration (off-set pupil) techniques of the ablation beam. The application of Mitomycin C as an adjunctive therapy in surface ablation is discussed. Different techniques of the phototherapeutic keratectomy (PTK) are described according to its indications. Addressing the eye at the end of the operation and post operative medications and recommendations are well addressed. This chapter gives also a full explanation of the laser ablation profiles, consisting of plain, optimized, aspheric (Q-guided), aspheric aberration-free, and wavefront guided profiles; the latter being discussed in full details in a step-wise demonstration, starting from taking the wavefront capture, going through determining the refraction, analysing the data and profile creation depending on a decision tree, and ending with the surgical technique with all considerations regarding alignment and registration, centration, eye tracking, nomogram adjustment and flap creation. Since surface ablation is currently being applied in combination with corneal cross linking, special considerations and precautions are to be known. All indications, contraindications, conditions, considerations and recommendations of this combination are well highlighted in this chapter. Another refractive option is described, the phakic IOL (PIOL) implantation. Types of PIOL, indications, conditions, work up and patient education are all mentioned in details. Finally, the refractive lens exchange (RLE) or what is also known as clear lens extraction (CLE) is presented as an alternative refractive option in very limited indications. However, criteria of patient selection, preoperative evaluation and surgical techniques are discussed. All types of monofocal, multifocal and accommodative IOLs are highlighted, including flexible, rigid, sharp-edged, square-edged, aspheric, heparin coated, toric IOLs, adjustable IOLs, IOLs with blue light filters, refractive, diffractive and refractive-diffractive multifocal IOLs. Criteria of selection of IOL and limitations are also highlighted. Chapter six: Rules and Guidelines in Refractive Surgery This chapter is an entrance to refractive surgery world. It mentions all rules and recommendations that guide the surgeon to take the right decision and to determine precisely all the aspects of their decision, such as type and amount of correction. Clear examples are used to clarify each rule and recommendation. Thickness rules are presented and supported with figures to explain the thickness ablation profiles in different refractive error situations; nine residual stromal bed rules are then discussed. K-reading rules are then presented, including flat K, steep K, average K, and astigmatism rules; with the latter having three types, myopic, hyperopic and mixed astigmatism rules. The nine probabilities of topographic and manifest astigmatism disparity are discussed with tables and examples to clarify them. Other rules are also mentioned including sub optimal correction rule, Q-value and ASSIS nomogram, pupil centre and angle kappa rule, pupil diameter considerations, cyclotorsion, amblyopia and enhancement concepts. Chapter seven: Clinical Approach This chapter represents a comprehensive approach to the refractive surgery candidate. It consists of three parts, part 1, the psychosocial approach, part 2, the medical approach, and part 3, the A-to-Z examination approach. Part 1 describes psychosocial considerations that should be put in mind when the candidate is first dealt with, such as type of personality and demands, in addition to some ethical aspects that the surgeon should pay attention to. Part 2 consists of patient history taking, which is composed of social history, ocular history and general health history. In ocular history, the candidate is asked about his refractive history, use of contact lenses, dry eye symptoms, watering eye, chronic allergy or infection, ocular trauma, previous ocular surgeries, ectatic corneal disorders, glaucoma, recurrent corneal erosions and use of any topical medications. Due the importance of dry eye syndrome (DES) and its effect on the results of refractive surgery, it is discussed in full details in terms of definition, pathophysiology and etiology, classification supported with a flow chart, investigations, impact on photorefractive surgery, predisposing factors, prevention and treatment. Part 2 discusses all the underlying systemic conditions that have an effect on candidate selection, decision making, incidence of complications and treatment results. These include diabetes, systemic hypertension, allergic and atopic diseases, collagen vascular diseases and inflammatory disorders, keloid formation diseases, pregnancy and nursing, immunodeficiency diseases, medications and others conditions. Finally, part 3 is also concerned about family history taking since there are some diseases that may not be encountered in the candidates themselves but in their parents or relatives, such as ectatic corneal disorders, which classify the apparently normal candidates as having forme fruste keratoconus (FFKC) and hence alter the decision. Part 3 presents A-to-Z examination of the candidates, starting with tests for visual acuity, going through clinical refraction, pupillometry, tear film tests, IOP measurement, determination of the non-dominant eye, studying ocular motility, considering orbital and ocular anatomy, slitlamp biomicroscopy, and ending with fundoscopy. All details are mentioned with their impact on patient selection and the best choice of refractive surgery. Chapter eight: Avoidable Refractive Surgery Complications Refractive surgery is not risk free. As many complications were and are encountered in this field, most of them are avoidable. This chapter deals with those complications that can be avoided if guidelines, rules and recommendations are followed. First, this chapter starts with those complications encountered in photorefractive surgery. They are divided into intra- and early post-operative, and late post-operative complications. The intra- and early post-operative complications consist of flap complications, such as thin and irregular flaps, button hole and pseudo button hole, incomplete flap, free flap, and distorted or displaced flap; flap-interface complications, such as infectious keratitis, diffuse lamellar keratitis (DLK), pressure induced stromal interface keratitis (PISK), central toxic keratitis (CTK), marginal sterile corneal infiltrates; and corneal melting. The late post-operative complications include dry eye syndrome (DES), epithelial ingrowth, iatrogenic ectasia, and haze. All these complications are discussed in full details in terms of definition, etiology, predisposing factors, clinical presentation, classification and grading, diagnosis, differential diagnosis, preventive measures and management. A large number of slitlamp, anterior OCT and tomography images are used to illustrate the complications in a unique method that rarely can be found in any textbook. In addition, iatrogenic ectasia is discussed in depth, presenting up-to-date information in regard with risk factors and the risk score system. Second, this chapter presents complications related to phakic IOL implantation, dividing them into intraoperative and postoperative ones. They include ocular hypotony, iris prolapse, choroidal hemorrhage, damage to the natural crystalline lens, endothelium or iris, ocular hypertension, pupillary block, acute uveitis, chronic inflammation, decentration, displacement, or rotation of PIOL, dislocation of PIOL, corneal edema, progressive endothelial cell loss, residual refractive error, pigment dispersion, cataract, iris atrophy and pupil ovalization. Finally, this chapter mentions specific complications related to refractive lens exchange in myopic patients, such as retinal detachment, choroidal neovascularization and macular degeneration. Chapter nine: Case Study Chapter nine is the last chapter. It starts by outlining general guidelines and explaining the step-by-step systematic methodology in reading and interpreting tomography and wavefront data. Then it presents nine clinical cases that were selected carefully, presented in a practical method, and discussed in a systematic critical thinking in order to build in readers the skills that are necessary in their practice. Finally, although this book is aimed at all those who need some initial assistance in starting their refractive surgery, this book is also aimed at providing current and future refractive surgeons with up-to-date information. The reader will find in this book a modern perspective on this field.
Posted on: Sat, 11 Oct 2014 18:56:47 +0000
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